Guidance for Industry and Other Stakeholders: Redbook 2000 : Toxicological Principles for the Safety Assessment of Food Ingredients

Administrative guidance, not enacted legislation. This captured publisher edition preserves the listed document and attachments; later developments are not independently consolidated.

July 2000; Revised July 2007
Additional copies are available from:
Office of Food Additive Safety, HFS-200
Center for Food Safety and Applied Nutrition
Food and Drug Administration
5001 Campus Drive
College Park, MD 20740
(Tel)301-436-1200
http://www.cfsan.fda.gov/guidance.html
U.S. Department of Health and Human Services
Food and Drug Administration
Center for Food Safety and Applied Nutrition
July 2000; Updated July 2007
Note to reader: Individual chapters/sections of this internet version
of "Redbook" are available as linked documents via the Table of
Contents. The date of revision for each chapter and /or chapter
section is provided in the Table of Contents and the individual
documents. These revisions supersede previous versions of
Redbook
A. 	Introduction 4 (November 2003)
B. 	General Recommendations for Toxicity Studies
Redbook 2000
Guidance for Industry and Other Stakeholders
Toxicological Principles for the Safety Assessment of Food
Ingredients
Redbook 2000
Table of Contents
I Introduction 1 (July 2007)
II. Agency Review of Toxicology Information Submitted in
Support of the Safety Assessment of Food Ingredients (available in
1993 Draft "Redbook II" 2)
III Recommended Toxicity Studies 3 (July 2007)
IV. Guidelines for Toxicity Studies
Food
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Redbook 2000
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1. 	General Guidelines for Designing and Conducting Toxicity
Studies 5 (November 2003)
2. 	Guidelines for Reporting Results of Toxicity Studies 6 (November
2003)
3. 	Pathology Considerations in Toxicity Studies 7 (July 2000)
4. 	Statistical Considerations in Toxicity Studies 8 (July 2000)
5. 	Diets for Toxicity Studies (available in 1993 Draft "Redbook II" 9 )
C. 	Guidelines for Specific Toxicity Studies
1. 	Short-Term Tests for Genetic Toxicity 10 (July 2000)
a. 	Bacterial Reverse Mutation Test 11 (July 2000)
b. 	In vitro Mammalian Chromosomal Aberration Test 12 (November
2003)
c. 	In vitro Mouse Lymphoma TK 13 +/- Gene Mutation Assay 14 (April
2006)
d. 	In vivo Mammalian Erythrocyte Micronucleus Test 15 (July 2000)
2. 	Acute Oral Toxicity Tests (available in 1993 Draft "Redbook II" 16 )
3. 	Short Term Toxicity Studies
a. 	Short-Term Toxicity Studies with Rodents 17 (November
2003)
b. 	Short-Term Toxicity Studies with Non-Rodents 18
(November 2003)
4. 	Subchronic Toxicity Studies
a. 	Subchronic Toxicity Studies with Rodents 19 (November
2003)
b. 	Subchronic Toxicity Studies with Non-Rodents 20
(November 2003)
5. 	Chronic Toxicity Studies
a. 	Chronic Toxicity Studies with Rodents 21 (July 2007)
b. 	One-Year Toxicity Studies with Non-Rodents 22 (November
2003)
6. 	Carcinogenicity Studies with Rodents 23 (January 2006)
7. 	Combined Chronic Toxicity/Carcinogenicity Studies with
Rodents 24 (July 2007)
8. 	In Utero Exposure Phase for Addition to Carcinogenicity Studies
with Rodents 25 (July 2007)
9. 	Reproduction and Developmental Toxicity Studies
a. 	Guidelines for Reproduction Studies 26 (July 2000)
b. 	Guidelines for Developmental Toxicity Studies 27 (July
2000)
10. 	Neurotoxicity Studies 28 (July 2000)
A. 	Introduction
B. 	Metabolism and Pharmacokinetic Studies
C. 	Immunotoxicity Studies
V. Additional Studies (available in 1993 Draft "Redbook II" 29 )
VI. Human Studies
Redbook 2000
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078044.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078310.htm
4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078311.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078315.htm
6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078409.htm
7. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
9. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
10. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078321.htm
11. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078330.htm
12. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078332.htm
A. 	Clinical Evaluation of Food Ingredients (available in 1993 Draft "Redbook
II" 30 )
B. 	Epidemiology Studies 31 (October 2001)
1
This guidance has been prepared by the Office of Food Additive Safety in
the Center for Food Safety and Applied Nutrition at the U.S. Food and Drug
Administration.
2Toxicological Principles for the Safety Assessment of Direct Food Additives
and Color Additives Used in Food (also known as Redbook I), U.S. Food
and Drug Administration, Bureau of Foods (now CFSAN), 1982. May be
purchased from: National Technical Information Services (NTIS), 5285 Port
Royal Road, Springfield, VA 22161, Telephone (703) 605-6000, NTIS Order
Number PB83-170696.
3Toxicological Principles for the Safety Assessment of Direct Food Additives
and Color Additives Used in Food 1993 Draft "Redbook II" Table of
Contents 33
VII Glossary: Acronyms and Definitions 32 (April 2004)
Links on this page:
Redbook 2000
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13. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078336.htm
14. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078336.htm
15. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078338.htm
16. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
17. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078339.htm
18. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078342.htm
19. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078345.htm
20. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078346.htm
21. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078349.htm
22. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078348.htm
23. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078388.htm
24. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078393.htm
25. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078394.htm
26. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078396.htm
27. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078399.htm
28. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078323.htm
29. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
30. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
31. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078401.htm
32. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078404.htm
33. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
Redbook 2000
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
"Toxicological Principles for the Safety Assessment of Food Ingredients 2
" ("Redbook 2000") is the new name
for Toxicological Principles for the Safety Assessment of Direct Food Additives and Color Additives Used in
Food" that was originally published in 1982 ("Redbook I") and a draft revision was published in 1993
("Redbook II" 3 ). Major changes in this revised guidance are presented later in this chapter. This document
provides guidance to industry and other stakeholders (e.g. academia, other regulatory groups) regarding
toxicological information submitted to the Center for Food Safety and Applied Nutrition (CFSAN), Office of
Food Additive Safety (OFAS) regarding food ingredients. It is a guidance document that is intended to assist
petitioners and notifiers in:
z determining the need for toxicity studies
z designing, conducting, and reporting the results of toxicity studies
z conducting statistical analyses of data
z the review of histological data
z the submission of this information to the FDA as part of the safety assessment of food
ingredients.
The term "food ingredients", as used in this guidance, includes food additives and color additives used in food,
and those substances which are classified as food contact substances (formerly known as indirect food
additives), and those substances which are classified as generally recognized as safe (GRAS). The toxicity
studies included in this guidance document can also be used in the safety assessment of constituent residues.
Petitioners and notifiers are encouraged to become familiar with the information in this guidance document as
well as other toxicology related guidance information available via the following internet links when
considering the submission of a petition or notification:
Food and Color Additive (Petition) Program 4
Food Contact Substances Program 5
GRAS Notification Program 6
Redbook 2000: I Introduction
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter I. Introduction
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: I Introduction
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Additionally, sponsors are encouraged to discuss with the appropriate regulatory divisions in the OFAS the
extent and types of toxicity testing they are considering and the type of petition or notification they intend to
submit. FDA consistently has taken the position that various types of scientifically valid information may be
used to support a determination that the proposed use of an ingredient is safe. Sponsors should consult with
the FDA to discuss the use of alternative information to support a determination of safety for the food
ingredient prior to the submission of a petition or notification.
BACKGROUND
One of the responsibilities of the FDA and its CFSAN is to ensure the safety of food ingredients added to the
food supply in the United States. The "safety" of these ingredients is provided for in Sections 70.3 7 and
170.3 8 of Title 21 of the Code of Federal Regulations (CFR) as, a reasonable certainty that a substance is not
harmful under the intended conditions of use. Safety is generally determined by considering the potential
cumulative effect of the substance in consumers and the probable consumption of the substance in the diet.
The potential cumulative effects are determined by the outcome of toxicity studies and knowledge of
compounds and their structures.
FDA's Bureau of Foods (former name of CFSAN) published its guidance, "Toxicological Principles for the Safety
Assessment of Direct Food Additives and Color Additives Used in Food" (referred to as Redbook I) in 1982 to
provide guidance for sponsors regarding the submission of food additive petitions. A revised draft of this
document was issued in 1993 (see Notice of Availability, published in the Federal Register (FR) on March 29,
1993, 58 FR 16536) and is referred to as "Redbook II". The FDA has continued to review comments related to
this draft which were received from the regulated and scientific communities and other stakeholders.
Additionally, the FDA has considered publications and information regarding recent advances and increased
knowledge in toxicology, science and the food industry, and other authoritative guidance for toxicity testing in
preparing this guidance document.
Food additives are generally defined in Section 201 9 (s) of the Federal Food, Drug, and Cosmetic Act (the Act)
and in 21 CFR 170.3(e)(1) 10 as substances whose intended use results or may reasonably be expected to
result, directly or indirectly, in its becoming a component of food or otherwise affecting the characteristics of
food. Food additives have historically, therefore, been referred to as direct or indirect food additives. It is
generally understood that direct food additives are compounds that are directly added to the food to achieve a
technical effect (i.e., emulsification, sweetening) and indirect food additives include substances used in the
production, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding of
food (i.e., can coatings, paper and paperboard, sanitizers, and adhesives). In 1997, the Food and Drug
Administration Modernization Act 11 (FDAMA) amended the Act creating a more efficient notification process
for food contact substances. Color additives are generally defined in Section 201 12 (t) of the Act as a dye,
pigment or other substance which when added or applied to a food, drug, or cosmetic is capable of imparting
a color thereto. A GRAS substance is one whose safety has been evaluated by qualified experts, and the
determination of safety based on evidence and through scientific procedures to be safe under the conditions of
its intended use. A description of the eligibility for classification as GRAS can be found in 21 CFR 170.30 13
.
Additionally, in 1997 FDA issued a proposed rule (62 FR 18937 14 , April 17, 1997) to establish a voluntary
notification procedure for notifying FDA of a determination that a particular use of a substance is GRAS.
MAJOR CHANGES IN THE REVISED GUIDANCE
This section summarizes major changes between "Redbook 2000" and "Redbook II". In general, these
changes were derived from three major sources: 1) increased scientific knowledge and technological advances
since 1993; 2) comments received on the draft 1993 "Redbook II"; and 3) a desire to achieve consistency and
harmonization with guidance published by other agencies, countries, and international organizations, when
such action does not compromise FDA's ability to ensure the safety of food ingredients.
z The title of this guidance document was changed from "Toxicological Principles for the Safety
Assessment of Direct Food Additives and Color Additives Used in Food" ("Redbook II") to
"Toxicological Principles for the Safety Assessment of Food Ingredients" ("Redbook 2000") to
better describe the breadth of circumstances where this guidance is applicable. "Redbook 2000"
is the year that the first chapters of the revised Redbook became available on the internet.
Rather than change the name of this guidance document when another chapter is added or as
revisions are made, the decision was made to retain the name "Redbook 2000".
z "Redbook 2000" is designed as an electronic document available on the internet. It will not be
published as a printed and bound document as were previous versions.
z The overall format of this guidance document has changed to facilitate availability on the
Redbook 2000: I Introduction
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078717.htm
4. 	http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/default.htm
internet. Each chapter is a "stand alone" document and can be accessed independently. Because
of this, general information related to toxicity testing has been repeated in the separate chapters
so that information related to each type of study is complete.
z Chapter III. Concern Levels and Recommended Toxicity Tests in "Redbook II" has been reduced,
revised, and renamed "Recommended Toxicity Studies" in "Redbook 2000". Readers are directed
to petition and notification web sites for more specific guidance for recommended toxicity
studies.
z Chapter IV. C. 1. Short-Term Tests for Genetic Toxicity has been expanded with more complete
descriptions and explanations of four separate types of genetic tests.
z "Neurotoxicity Studies" guidance is now located in Chapter IV. Guidelines for Toxicity Studies.
"Neurotoxicity Studies" was previously located in "Redbook II", Chapter V. Additional
Recommended Studies.
z Chapter IV. C. 7 Combined Chronic Toxicity/Carcinogenicity Studies with Rodents in "Redbook II"
is now available in "Redbook 2000" in the following two chapters:
{ IV.C.5a. Chronic Toxicity Studies with Rodents
{ IV.C.7. Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
z Chapter VII. Emerging Issues has not been included in "Redbook 2000". Information related to
the emerging issues presented in the "Redbook II" has been considered and incorporated in
relevant chapters of "Redbook 2000". The reader is encouraged to become familiar with
additional information available via the OFAS web page 15 and to contact OFAS 16 with specific
questions.
FLEXIBILITY IN GUIDANCE FOR TOXICITY TESTING
FDA's guidance for toxicity studies for food ingredients continue to emphasize that there is no substitute for
sound scientific judgement. This guidance presents recommendations--not hard and fast rules. If an
investigator believes that he/she can provide the Agency with useful toxicological information by modifying a
recommended study protocol, and is able to support the modification with sound scientific arguments, then
the investigator should propose the modified protocol to the appropriate program division within OFAS. As
always, petitioners and notifiers should consult with the FDA prior to and during the design of study protocols
for toxicity studies and/or before commencement of studies.
FDA's guidance documents, including this guidance, do not establish legally enforceable responsibilities.
Instead, guidances describe the Agency's current thinking on a topic and should be viewed only as
recommendations, unless specific regulatory or statutory requirements are cited. The use of the word should
in Agency guidances means that something is suggested or recommended, but not required.
For the benefit of the reader and because each of the chapters and chapter sections of Redbook 2000 are
stand alone documents and can be accessed independently on the internet, FDA is repeating the disclaimer in
the box at the beginning of each chapter and chapter section of Redbook.
Links on this page:
Redbook 2000: I Introduction
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5. 	http://www.fda.gov/Food/FoodIngredientsPackaging/FoodContactSubstancesFCS/default.htm
6. 	http://www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/GRASNotification
Program/default.htm
7. 	http://ecfr.gpoaccess.gov/cgi/t/text/text-idx/?
c=ecfr&sid=c049a9925f4a9aa66b8e8a66b4efc413&rgn=div8&view=text&node=21:1.0.1.1.24.1.31.1&id
no=21
8. 	http://ecfr.gpoaccess.gov/cgi/t/text/text-idx/?
c=ecfr&sid=c049a9925f4a9aa66b8e8a66b4efc413&rgn=div8&view=text&node=21:3.0.1.1.1.1.1.1&idno
=21
9. 	http://www.fda.gov/opacom/laws/fdcact/fdcact1.htm
10. 	http://ecfr.gpoaccess.gov/cgi/t/text/text-idx/?
c=ecfr&sid=c049a9925f4a9aa66b8e8a66b4efc413&rgn=div8&view=text&node=21:3.0.1.1.1.1.1.1&idno
=21
11. 	http://www.fda.gov/RegulatoryInformation/Legislation/FederalFoodDrugandCosmeticActFDCAct/Significa
ntAmendmentstotheFDCAct/FDAMA/default.htm
12. 	http://www.fda.gov/opacom/laws/fdcact/fdcact1.htm
13. 	http://ecfr.gpoaccess.gov/cgi/t/text/text-idx/?
c=ecfr&sid=c049a9925f4a9aa66b8e8a66b4efc413&rgn=div8&view=text&node=21:3.0.1.1.1.1.1.1&idno
=21
14. 	http://www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/ucm083058.htm
15. 	http://www.fda.gov/Food/FoodIngredientsPackaging/default.htm
16. 	http://www.fda.gov/Food/FoodIngredientsPackaging/ucm081905.htm
Redbook 2000: I Introduction
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Chapter II
Agency Review of Toxicology Information
in Petitions for Direct Food Additives
and Color Additives Used in Food
A. 	Introduction
The food additive petition review process came into existence in 1958 when Congress enacted the Food
Additives Amendment 1 to the Federal Food, Drug, and Cosmetic Act (the Act). 2 This Amendment provides a
pre-market safety evaluation process for new substances added to food, "food additives." A similar statute, the
Color Additive Amendments of 1960, 3,4 created analogous requirements for color additives used in foods, drugs,
cosmetics, or medical devices. "Color additive" used in food is defined in section 201(t) of the Act; "food
additive" is defined in section 201(s) of the Act.
Since 1958, before a food additive may be used, an authorizing regulation must be in effect. Approval of
a petition for an additive and issuance of an authorizing regulation require that the Agency conclude that the
additive is safe for its intended conditions of use. This safety requirement, embodied in section 409(c)(3)(A), is
often referred to as the general safety clause for food additives. When the proponent of the proposed use of the
additive has shown that the additive is safe for its intended use, the Agency publishes a regulation in the Federal
Register establishing permitted conditions for the use of the additive.
When a petition for a direct food additive or color additive used in food is submitted to the Agency, or
when the petitioner first contacts FDA, a Consumer Safety Officer (CSO) generally is assigned to the petition.
One of the CSO's tasks is to coordinate FDA's review of the petition. When appropriate, the CSO can arrange for
the petitioner to meet with other individuals in the Agency to discuss specific issues or problems that arise during
review of the petition. All communication with the Agency concerning the status or review of the petition should
be made through the assigned CSO. General information about the petition review process has been published; 5
specific questions should be addressed to the CSO assigned to the petition.
The Act and the Code of Federal Regulations 6 specify the basic elements that a petition must contain.
One of these elements is safety data on the additive, which is usually provided in the form of toxicity studies.
Toxicologists, pathologists, and mathematicians evaluate any toxicity studies included in the petition. If
appropriate, toxicologists can recommend that carcinogenicity studies be evaluated by special CFSAN
committees: the Cancer Assessment Committee (CAC) and the Quantitative Risk Assessment Committee
(QRAC); for more information on these committees, see Chapter II C 5 i and ii.
Review of toxicity studies and other toxicology information results in an estimate of the acceptable daily
intake (ADI) for the direct food additive or color additive used in food. The ADI is typically based on the dose
level of the additive in animal studies that was shown to cause no adverse effect, multiplied an appropriate safety
factor (often 1/100; see Section 201(s) of the Act 2). Chronic ingestion of the additive at the ADI is considered
consistent with a reasonable certainty of no harm.
FDA urges individuals or corporations preparing to submit petitions for direct food additives or color
additives used in food to consult with the Agency early in the planning stages. For example, before the petition is
submitted, petitioners can submit toxicity study protocols to FDA for review by Agency scientists. This can help
the petitioner perform toxicity studies and prepare data in a form that will expedite the Agency's review of the
information in the petition (for more information on expediting review, see Chapter II B).
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This document delineates the toxicology information deemed appropriate for assessing the safety of direct
food additives and color additives used in food. However, guidelines contained in this document are only one
possible approach among many to providing the toxicological basis for an assessment of safety. We urge
petitioners to discuss alternative approaches and toxicity test protocols with the Agency before toxicity tests are
begun.
II B. Expediting Review of Toxicology Information
The Agency recommends that petitioners use the following approaches to minimize requests for
additional data and to expedite review of direct food additive and color additive petitions:
4 Make sure that petitions are formatted properly and contain complete and adequate information before
submitting them for review. Guidelines and recommendations contained in this publication should be
consulted before the petition is submitted.
4 Initiate interactions between petitioner's representatives and Agency CSOs and scientists before the
petition is submitted. Such interactions can involve Agency review of toxicity study protocols and
Agency recommendations about the extent of toxicity testing that may be recommended to adequately
assess the safety of the food additive or color additive used in food.
4 Submit toxicology data in machine-readable form. During review of the safety of a food additive or
color additive used in food, it may be necessary for scientific reviewers to re-analyze some of the data in a
submission. A large proportion of the work in such a re-analysis is computer entry and verification of
data. Therefore, much time would be saved if data are submitted in a machine-readable form (magnetic
tape for the IBM mainframe standard or floppy disks for IBM personal computers. Please note that the
Agency no longer has the capability to read punched cards). General guidelines for submitting machine-
readable data follow, but petitioners are urged to contact the Agency before submitting machine-readable
data to discuss modifications to these guidelines.
4 Enclosed with the machine-readable data should be:
i) the name of a contact person;
ii) a printout of the first 100 to 200 records; and
iii) the layout of the data. This would include the location of each variable in the record, the
type of variable (e.g. character, integer), the permissible range of values, and information about
how missing data are stored.
4 Magnetic tape format needs to be 9-track, with 6250 bpi preferred (although 800 and 1600 bpi are also
readable). Data should be recorded in IBM-EBCDIC or ASCII, or should be in IBM-TSO or statistical
package datasets; please consult with the Agency statisticians about appropriate datasets. Interior labels
should be IBM standard with volume number and dataset names. Unlabeled tapes should be
accompanied by the record format, record length, blocking factor, and the name of the program that
created the tape.
4 Floppy disks should be submitted in duplicate; these should be copy-protected because accidental
erasure and destruction of disks can occur. The data should be submitted in a form readable by software
programs to which the Agency has access; please consult with Agency statisticians about acceptable
software.
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II C. Evaluating Toxicology Information
1. 	Introduction
Toxicity testing requirements for assessing the safety of food and color additives used in food have
evolved over the past years as knowledge in the field of toxicology has expanded. While short-term or acute
studies were considered adequate even for major food additives several decades ago, today's recommendations
generally include comprehensive, long-term toxicity studies. CFSAN toxicologists exercise their best scientific
judgement in determining what toxicity studies are needed for the Agency to adequately assess the safety of a
direct food additive or color additive used in food. In making these decisions, the toxicologists take into account
what is already known about the properties of a compound, its intended conditions of use, and current standards
for toxicity testing.
From data submitted by the petitioner in support of the safety of a direct food additive or color additive
used in food, Agency toxicologists determine the no-observed-effect level (NOEL), select an appropriate safety
factor, and calculate the acceptable daily intake (ADI) for the substance. These steps are briefly summarized
below.
2. 	No-Observed-Effect Level (NOEL)
Non-treatment-related variations in the incidence of toxic endpoints occur and may depend on a number
of factors, including the source of the animals, sex, genetic variations, diet, age at death, environmental conditions
and the histological criteria used by pathologists.
However, Agency scientists determine the most sensitive treatment-related toxic endpoint (adverse effect)
from the data submitted in support of the petition. This endpoint is the adverse or toxic effect that occurs in test
animals at the lowest exposure to the test substance. The highest exposure that does not produce this adverse
effect is called the no-observed-effect level (NOEL) or the no-observed-adverse-effect level (NOAEL).
3. 	Safety Factors
Use of safety factors is based on the observation that toxic substances usually have thresholds below
which toxic effects cannot be detected. The safety factor attempts to account for differences between animals and
humans and differences in sensitivity among humans. Use of the safety factor is intended to provide an adequate
margin of safety for consumers.
For non-cancer endpoints, the NOEL is divided by a safety factor to obtain an estimate of the maximum
acceptable daily intake (ADI) of the additive for humans. The selection of a safety factor is based on the
biological significance of the endpoint, uncertainties inherent in extrapolating information about adverse effects
from toxicity studies in animals to human populations, and other judgmental factors. The food additive procedural
regulations (21 CFR 170.22) state that a safety factor of 100 will be used as a general rule in applying animal test
data to man. However, exceptions to a safety factor of 100 are permitted in accordance with the nature and extent
of data available and the circumstances of use of the food additive. For example, safety factors may be modified
because of potentially sensitive sub-populations such as children, geriatrics, individuals with deficiency states, and
lack of developed enzyme metabolic systems.
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II C 4. Acceptable Daily Intake (ADI)
The acceptable daily intake (ADI) is generally estimated by dividing the no-observed-effect level (NOEL)
of a test substance by the safety factor. The NOEL may be expressed as mg test substance per kg body weight of
the test animal or as percent or ppm (parts per million) of the test diet for the animal. The ADI is usually
expressed in mg additive per kg body weight of humans. A food additive generally is considered safe for its
intended use if the estimated daily intake (EDI) of the additive is less than, or approximates, the ADI. Because the
ADI is calculated to protect against the most sensitive adverse effect, it also protects against other adverse effects
occurring at higher exposures to the ingredient.
5. 	Carcinogenic Risk Assessment
FDA has found risk assessment to be useful for estimating the risk from carcinogenic contaminants of
food or color additives used in food, for helping the Agency to set priorities, and for determining the urgency of a
regulatory action. 7
Under the general safety clause of the Act, FDA has used risk assessment procedures to determine the
upper limit of risk to the consumer from the presence of a carcinogenic contaminant or constituent chemical. For
example, FDA approved for permanent listing D&C Green No. 6, which had not been shown to be a carcinogen in
appropriate tests, even though it contains the carcinogenic impurity, para-toluidine. In this decision, FDA stated
its belief that the lifetime upper limit of risk could adequately be estimated from animal data and extrapolated to
humans. Although FDA continues to be concerned about carcinogenic contaminants in the food supply, the
Agency believes that this approach can be used, where appropriate, without compromising FDA's mandate to
protect the public health.
a. 	CFSAN's Cancer Assessment Committee (CAC)
The Cancer Assessment Committee (CAC) is comprised of CFSAN experts in such fields as pathology,
toxicology, mathematics, food chemistry and technology, epidemiology, and nutrition. These experts are charged
with ensuring a uniform and consistent scientific approach for dealing with diverse problems of carcinogenicity
throughout the broad regulatory purview of CFSAN. The CAC reviews all lifetime feeding studies submitted to
the Agency in support of the safety of direct food additives and color additives used in food. The risk assessment
process also can be triggered when a newly petitioned or previously regulated food or color additive presents a
question of possible carcinogenicity. If the CAC determines that a substance is a carcinogen, and if it is believed
that a quantitative risk assessment may have impact on the regulation of the substance, the CAC informs the
Quantitative Risk Assessment Committee (QRAC, see Chapter II C 5 b) of this decision.
Figure 1 is a flow chart depicting in schematic fashion the groups involved in the risk assessment process
at CFSAN. Figure 2 identifies the steps involved in risk assessment at CFSAN; each of the steps in Figure 2 is
associated with a particular group or set of groups in Figure 1.
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000013

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II C 5. Carcinogenic Risk Assessment Continued
As indicated in Figure 1, the CAC plays a central role in the risk assessment process at CFSAN. This
standing committee, which was established in 1978, is made up of 10 CFSAN individuals with expertise in the
various scientific disciplines related to chemical carcinogenesis: pathology, toxicology, mathematics, and food
chemistry and epidemiology. The decisions of the CAC with respect to issues of science are authoritative and
invariably form the basis for CFSAN's recommendations to the Commissioner.
In addition to reviewing information presented by the disciplines indicated in Figure 1, the CAC may
request additional information from internal and external experts, such as a review of available epidemiological
data or a special review of mutagenicity data. The CAC may choose to postpone a final decision on the
carcinogenicity of a compound pending the outcome of ongoing or anticipated animal or analytical experiments.
In some cases, the CAC may request that CFSAN pathologists review microscope slides from an animal bioassay.
External scientific peer review is sometimes requested by the CAC when a particularly difficult or controversial
scientific issue is involved.
In general, FDA and CFSAN follow the National Research Council guidelines for risk assessment,
described in Risk Assessment in the Federal Government: Managing the Process. 8 FDA and CFSAN also follow
the set of principles for risk assessment contained in the 1985 Office of Science and Technology Policy document,
"Chemical Carcinogens; A Review of the Science and its Associated Principles". 9,10
There are no universally agreed upon ways of evaluating carcinogenicity data. It is necessary that there
be interaction between pathologist, toxicologist and statistician. The role of the pathologist is to decide whether an
observed lesion is cancerous or noncancerous. 11 The role of the toxicologist is to determine whether the lesion is
related to the treatment. The statistician's role is to analyze the mathematical probability of occurrence of the
tumors by chance or as a result of treatment.
Some suggested approaches to the assessment of the evidence of carcinogenicity of a substance are
discussed in the following sections.
i) 	Evaluation of the Adequacy of the Design and Conduct of the Bioassay: The first step in the
analysis is a general review of the adequacy of design and conduct of the bioassay to decide whether it is
acceptable for evaluation and for deriving conclusions about safety. For example: Was the test chemical
properly identified and characterized? Were an adequate number of animals of each sex used per group?
Was the test chemical administered for the major part of the life span of the animals? Did sufficient
numbers of animals in each group survive long enough for possible late-developing tumors to be
manifested? Were there unforeseen events, such as an outbreak of infectious disease, that might
invalidate the bioassay? Did the bioassay utilize adequate matched control animals for statistical
comparison? Were detailed pathological examinations performed for every tissue?
ii) 	Evaluation of the Possible Increase in Tumor Incidence: Since it is generally believed that
cancers arise independently in various parts of the body, it has become customary to treat each potential
target site (e.g., brain, lung, liver, kidney, urinary bladder) separately for evaluation. One general
exception is the evaluation of types of tumors that may be multicentric in origin, including leukemia and,
possibly, tumors originating in blood vessels or nerves, such as hemangioendotheliomas or
neurofibrosarcomas. In general, tumor incidence is defined as the number of tumor-bearing animals
having tumors at a specific organ site divided by the total number of animals with that organ examined
histopathologically.
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II C 5. Carcinogenic Risk Assessment Continued
Judgment of an experienced pathologist is important for proper diagnosing and grouping of lesions for
statistical analysis to determine whether or not observed increases in tumor incidence implicate a compound as a
carcinogen. The grouping of tumors for statistical evaluation should be based on commonality of histogenic
origin. Because it is frequently a matter of arbitrary definition and expert pathologists may disagree about how to
designate tumors on the borderline of the continuum between benign and malignant, and because of practical
difficulties in categorizing certain tumors as benign or malignant, it is usually necessary to combine the incidence
of certain benign tumors with that of malignant tumors occurring in the same tissue and organ for statistical
evaluation.
Having recorded the tumors present for each animal, the statistical analysis can be undertaken to evaluate
the internal consistency of the data, the reproducibility of the test results, the level of statistical significance, the
increase in tumor incidence, the evidence for dose-response relationship or shortened latency period, etc. Methods
of statistical analysis for carcinogenicity are available. 12,13,14
iii) 	Evaluation of the Extent of Evidence for Carcinogenicity: Because the power of carcinogenesis
bioassays that use groups of a few dozen animals is relatively weak for determining carcinogenic activity,
it is not surprising that evidence of carcinogenicity is sometimes difficult to establish from a single
bioassay. This is so for several reasons, including problems of histological diagnosis, sensitivity of the
bioassay, and variability of the background tumor incidence. For these reasons, other correlative
information may be necessary to add to the weight of evidence of carcinogenicity of a chemical. In
general, the extent of the evidence for carcinogenicity can be determined by considering the following
information:
4 the number of species or strains with an increased tumor incidence;
4 the number of positive studies (with different routes of administration and/or doses), if tested
in more than one bioassay;
4 the degrees of tumor response (incidence, site, type, multiplicity, etc.);
4 evidence of structure-activity relationship;
4 prevalence of dose-response relationship;
4 the results of short-term tests for genetic toxicity;
4 the presence of preneoplastic lesions; and
4 a reduced latency for tumor development or increase in the severity (malignancy of the
neoplasia.
Other information, such as whether there was a shortened survival due to the toxicity of the test substance
or whether the chemical is tested at or near the MTD, can also add weight to or confound the evidence of
carcinogenicity. Information on dose-dependent or nonlinear kinetics from metabolic and pharmacokinetic studies
in experimental animals and humans can supplement the assessment of the potential carcinogenic hazard of the
additive to humans.
It should be noted that, although general approaches to animal carcinogenesis bioassays are well accepted
by the scientific community, opinions about the design, conduct, and interpretation of such test results are not
always in agreement and are often the source of scientific debate. This may be due, in large degree, to our lack of
knowledge about the mechanisms of cancer induction and progression. Because the Act prohibits the use of
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carcinogenic food and color additives, the interpretation of carcinogenicity test results has enormous potential
societal and economic impact. Consequently, proper assessment of carcinogenicity data has become an extremely
critical function of CFSAN.
b. 	CFSAN's Quantitative Risk Assessment Committee (QRAC)
The QRAC was formed in 1983. Although quantitative risk assessments were performed under the
auspices of the CAC prior to this, the QRAC was formed because of the need for an increasing number of
quantitative risk assessments related to food and color additive petitions. Based on its evaluation of all relevant
data on a substance, the CAC recommends to the QRAC the bioassays and epidemiological studies most
appropriate for low-dose extrapolation. The CAC also recommends to the QRAC the tissue site(s), species, and
sex most suitable for quantitative evaluation.
The QRAC then performs a quantitative risk assessment. This portion of the risk assessment process is
often controversial, even among experts. Currently, the QRAC uses a linear-at-low-dose approach, similar to that
described by Gaylor and Kodell. 15 The QRAC cannot determine the most probable expected human risk for
almost any case because of the uncertainties and sources of error inherent in quantitative risk assessment using
high-dose animal data. However, the QRAC believes that, in cases where dose-response data are suitable, it can
predict a lifetime upper limit of risk with some degree of confidence.
References
1. 	Food Additives Amendment, Section 409, Federal Food Drug, and Cosmetic Act (1958)
2. 	Federal Food Drug, and Cosmetic Act (1958)
3. 	Committee of Labor and Public Welfare [CLPW] (1988) A legislative history of the Federal Food, Drug,
and Cosmetic Act and its amendments. A report submitted by Mr. Hill from the Committee on Labor and
Public Welfare entitled "Food Additives Amendment of 1958. U.S. Senate report No. 2422 to accompany
H.R. 13254. Vol.14:913-937.
4. 	Color Additive Amendment, Section 706, Federal Food Drug, and Cosmetic Act (1958)
5. 	Rulis, A.M. (1990) The Food and Drug Administration's Food Additive Petition Review Process. Food
Drug Cosmetic Law J. 45:533-544.
6. 	The Act, Section 409 (b) of the U.S. Code of Federal Regulations, Title 21 (1992)
7. 	Lorentzen, R.J (1984) FDA procedures for carcinogenic risk assessment. Fd.Technol. 38(10):108-111.
8. 	National Research Council [NRC]. (1983) In, Risk assessment in the federal government: Managing the
process. Washington, D.C. National Academy of Sciences [NAS] Press. Washington D.C.
9. 	Office of Science and Technology (1985) In, Chemical carcinogens; A review of the science and its
associated principles.
10. 	Anonymous. (1986) Chemical carcinogens: A review of the science and its associated principles. A report
by the U.S. Interagency Staff Group on Carcinogenesis. Environ. Health Perspect. 67:201-282.
11. 	Dua, P.N. and Jackson, B.A. (1988) Review of pathology data for regulatory purposes. Toxicol.Path.
16:443-450.
12. 	Peto, R., Pike, M.C., Day, N.E., Gray, R.G., Lee, P.N., Parish, S., Peto, J., Richards, S. and Wahrendorf,
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J. (1980) Guidelines for simple sensitive significance tests for carcinogenic effects in long-term animal
experiments. In, Long-term and short-term screening assays for carcinogens: A critical appraisal.
International Agency for Cancer Research [IARC]. Lyon, France. Monograph Suppl. 2:311-426.
13. 	Bickis, M. and Krewski, D. (1985) Statistical design and analysis of the long-term carcinogenicity
bioassay. In, Toxicological risk assessment, Vol. 1, Biological and statistical criteria. (D.B. Clayson, D.
Krewski, and I. Munro eds.) CRC Press, Inc. Boca Raton, FL. pp.125-147.
14. 	McKnight, B. (1988) A guide to the statistical analysis of long-term carcinogenicity assays.
Fund.Appl.Technol. 10:355-364.
15. 	Gaylor, D.W. and Kodell, R.L. (1980) Linear interpolation algorithm for low dose assessment of toxic
substances. J.Environ.Path.Toxicol. 4:305-312.
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
This chapter provides a general description of how FDA determines which toxicological studies are
recommended in order for FDA to evaluate the safety of food ingredients (i.e., direct food additives, color
additives used in food, food contact substances, previously referred to as indirect food additives, etc.). A
determination that a reasonable certainty of no harm will result from the proposed use(s) of food ingredients
is required before manufacturers and distributors can market them in the United States (see sections 70.3 and
170.3 of Title 21 of Code of Federal Regulations). The determination of reasonable certainty of no harm is
contingent upon the results of toxicological studies, exposure information, and other types of information
submitted in petitions and notifications. Details related to the evaluation of toxicological information is
provided in Chapter II of Redbook. Safety data submitted for evaluation of Generally Recognized As Safe
(GRAS) substances and bioengineered foods may result from specialized tests which are not represented in
Redbook. In certain cases, the classical toxicological studies presented in Redbook may be recommended and
useful in the evaluation of these substances. The reader is directed to more specific guidance for each type of
submission as follows:
Food and Color Additives Program 2
z Questions and Answers about the Petition Process 3
z Guidance for Industry: Summary Table of Recommended Toxicological Testing for Additives Used
in Food 4
z Estimating Exposure to Direct Food Additives 5
z Concern Levels and Recommended Toxicity Tests for Direct Food Additives and Color Additives
Used in Food ("draft" 1993 Redbook II) 6
Food Contact Substance Notification Program 7
z Guidance for Industry: Preparation of Food Contact Notifications for Food Contact Substances:
Toxicology Recommendations 8
z Guidance for Industry: Preparation of Food Contact Notifications and Food Additive Petitions for
Food Contact Substances: Chemistry Recommendations 9
z Guidance for Industry: Preparation of Food Contact Notifications: Administrative 10
Redbook 2000: III Recommended Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter III. Recommended Toxicity Studies
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: III Recommended Toxicity Studies
Page 1 of 3	3/3/2010
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/default.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm078136.htm
4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm054658.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm074725.htm
6. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078759.pdf
7. 	http://www.fda.gov/Food/FoodIngredientsPackaging/FoodContactSubstancesFCS/default.htm
8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm081825.htm
9. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm081818.htm
10. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm081807.htm
GRAS Notification Program and Biotechnology 11
z Frequently Asked Questions About GRAS 12
z How to Submit a GRAS Notice 13
z Biotechnology 14
z List of Completed Consultations on Bioengineered Foods 15
Generally speaking, the determination of the types of toxicological studies that should be submitted as part of
a petition or notification for a food ingredient is based on information about the compound of interest as well
as the exposure to the compound via its proposed use(s). Information about the compound includes the
toxicological effects on various biological systems (i.e., nature of effect, target, magnitude of response per
unit dose, etc.) which may be derived from toxicological studies which have been conducted with this
compound. Toxicological information on a similar compound or knowledge about compounds with a similar
chemical structure or substructure may be helpful in instances where toxicological information on the
compound of interest is limited.
Detailed guidance for specific toxicity studies are not included in this chapter. Guidance for the conduct of
short-term studies for genetic toxicity, short-term toxicity studies with rodents and non-rodents, subchronic
toxicity studies with rodents and non-rodents, chronic toxicity studies with rodents and non-rodents,
carcinogenicity studies with rodents, combined chronic toxicity/carcinogenicity studies or chronic toxicity
studies with rodents, in-utero exposure phase for addition to carcinogenicity studies or chronic toxicity studies
with rodents, neurotoxicity, and reproduction and developmental toxicity studies, can be found in Chapter IV.
C. of Redbook 2000. Guidance to assist the petitioner and notifier in developing strategies for assessing the
metabolism and pharmacokinetics and immunotoxicity can be found in Chapter V of the "draft" 1993 Redbook
II.
It is important to note that as data from the recommended set of toxicity studies are obtained, the results
may be used to refine or adjust the type, sensitivity, and rigor of subsequent studies needed to evaluate the
potential toxicological effects of the compound.
Links on this page:
Redbook 2000: III Recommended Toxicity Studies
Page 2 of 3	3/3/2010
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11. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm081807.htm
12. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/ucm061846.htm
13. 	http://www.fda.gov/Food/FoodIngredientsPackaging/GenerallyRecognizedasSafeGRAS/ucm083062.htm
14. 	http://www.fda.gov/Food/Biotechnology/Announcements/default.htm
15. 	http://www.fda.gov/Food/Biotechnology/default.htm
Redbook 2000: III Recommended Toxicity Studies
Page 3 of 3	3/3/2010
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
The Agency published its first set of guidelines for toxicity studies for food additives and color additives used
in food in 1982 and the first revision in 1993. The guidelines presented in Chapter IV. of Redbook 2000 reflect
current scientific knowledge relevant to the design, conduct, and reporting of toxicity studies used in the
safety evaluation of food ingredients.
Information contained within Chapter IV.B. provides recommendations which generally apply to all types of
toxicity studies and should be considered when designing toxicity studies. Chapter IV. B. currently includes:
"General Guidelines for Designing and Conducting Toxicity Studies" (IV.B.1.), "Guidelines for Reporting the
Results of Toxicity Studies" (IV.B. 2.), "Pathology Considerations in Toxicity Studies" (IV.B.3.), and "Statistical
Considerations in Toxicity Studies" (IV.B.4.). Relevant information contained in the "General Guidelines for
Designing and Conducting Toxicity Studies" (IV.B.1.) has also been incorporated into the specific studies
(IV.C.3.-5.) in Redbook 2000, for your convenience.
Information presented within Chapter IV.C. of Redbook 2000 provides recommendations for the following
specific types of toxicity studies:
1. 	IV.C.1. Short-Term Tests for Genetic Toxicity
2. 	IV.C.1.a. Bacterial Reverse Mutation Test
3. 	IV.C.1.b. In vitro Mammalian Chromosomal Aberration Test
4. 	IV.C.1.c. In vitro Mouse Lymphoma Thymidine Kinase Gene Mutation Assay
5. 	IV.C.1.d. In vivo Mammalian Erythrocyte Micronucleus Test
6. 	IV.C.3.a. Short-Term Toxicity Studies with Rodents
7. 	IV.C.3.b. Short-Term Toxicity Studies with Non-Rodents
8. 	IV.C.4.a. Subchronic Toxicity Studies with Rodents
9. 	IV.C.4.b. Subchronic Toxicity Studies with Non-Rodents
10. 	IV.C.5 One-Year Toxicity Studies with Non-Rodents
11. 	IV.C.9.a. Guidelines for Reproduction Studies
Redbook 2000: IV. A Introduction: Guidelines for Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV. A. Introduction: Guidelines for Toxicity Studies
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV. A Introduction: Guidelines for Toxicity Studies
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
12. 	IV.C.9.b. Guidelines for Developmental Toxicity Studies
13. 	IV.C.10. Neurotoxicity Studies
Other specific toxicity studies listed in the Table of Contents of Redbook 2000 will be added in the coming
months. These include: acute toxicity studies and/or alternatives (Chapter IV.C.2.), carcinogenicity studies
with rodents (Chapter IV.C.6.), combined chronic toxicity/carcinogenicity studies with rodents (Chapter
IV.C.7.), and in utero exposure phase for addition to carcinogenicity studies (Chapter IV.C. 8.).
Links on this page:
Redbook 2000: IV. A Introduction: Guidelines for Toxicity Studies
Page 2 of 2	3/3/2010
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Guidelines that are common to several or all toxicity studies are described in this section. Guidelines for
specific recommended toxicity studies are found in Chapter IV.C., including: genetic toxicity studies (Chapter
IV.C.1.), acute oral toxicity studies (Chapter IV.C.2. in the 1993 draft "Redbook II"), short-term toxicity
studies with rodents and non-rodents (Chapter IV.C.3.a. and b., respectively), subchronic toxicity studies with
rodents and non-rodents (Chapter IV.C.4.a. and b., respectively), one-year toxicity studies with non-rodents
(Chapter IV.C.5.), carcinogenicity studies with rodents (Chapter IV.C.6. in the 1993 draft "Redbook II"),
combined chronic toxicity/carcinogenicity studies with rodents (Chapter IV.C.7. in the 1993 draft "Redbook
II"), in utero exposure phase for addition to rodent toxicity studies (Chapter IV.C.8. in the 1993 draft
"Redbook II"), reproduction and developmental toxicity studies (Chapter IV.C.9.a. and b., respectively), and
neurotoxicity studies (Chapter IV.C.10.). We encourage sponsors/submitters of petitions/notifications to also
become familiar with the Guidance for Reporting Results of Toxicity Studies (Chapter IV.B.2.), Pathology
Considerations in Toxicity Studies (Chapter IV.B.3.), and Statistical Considerations in Toxicity Studies
(Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to this section of the 1993 draft "Redbook II" have been made following
consultation with other authoritative guidelines and publications 1-8
.
Redbook 2000: IV.B.1 General Guidelines for Designing and Conducting Toxicity
Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.B.1. General Guidelines for Designing and Conducting Toxicity Studies
General Guidelines for Toxicity Studies
I. Good Laboratory Practice
Food
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Redbook 2000: IV.B.1 General Guidelines for Designing and Conducting Toxicity Studies
Page 1 of 11	3/3/2010
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Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"9
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines.
These guidelines are for studies with rodents (usually rats) and non-rodents (usually dogs); if other species
are used, modifications of these guidelines may be necessary. Both male and female test animals, that are
healthy and have not been subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies. The selection of the use of inbred, out-bred, or hybrid rodent strains for toxicity tests should be based
upon the scientific questions to be answered. Additionally, it is important that test animals come from well-
characterized and healthy colonies. Because recent information suggests survivability problems exist for some
strains of rats, test animals should be selected that are likely to achieve the recommended duration of the
study. FDA encourages petitioners and notifiers to consult with Agency scientists before toxicity testing is
begun if they have questions about the appropriateness of a particular species, strain, or substrain.
Testing should be performed on young animals, with dosing beginning as soon as possible after weaning and
following an acclimation period of at least 5 days.Dosing of rodents should begin no later than 6 to 8 weeks of
age. When dogs are used, dosing should begin no later than 4 to 6 months of age.
Equal numbers of males and females of each species and strain should be used for the study. In general, for
subchronic toxicity studies, experimental and control groups should have at least 20 rodents per sex per group
or at least 4 dogs per sex per group. Ten rodents/sex/group may be acceptable for subchronic rodent studies
when the study is considered to be range-finding in nature or when longer term studies are anticipated. These
recommendations will help ensure that the number of animals that survive until the end of the study will be
sufficient to permit a meaningful evaluation of toxicological effects.
If interim necropsies are planned, the number of animals per sex per group should be increased by the
number scheduled to be sacrificed before completion of the study; for rodents, at least 10 animals per sex per
group should be available for interim necropsy.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal must be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tatoo).
Animals should be housed one per cage or run (single-caged) except during mating and lactation and for
acute toxicity studies. This recommendation reflects three points of consideration:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
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animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
In general, feed and water should be provided ad libitum to animals in toxicity studies, and the diets for these
studies should meet the nutritional requirements of the species 10-13 for normal growth and reproduction.
Unless special circumstances apply which justify otherwise, care should be taken to ensure that the diets of
the compound treated groups of animals are isocaloric (equivalent in caloric density) with and contain the
same levels of nutrients (e.g., fiber, micronutrients) as the diets of the control group. Unrecognized or
inadequately controlled dietary variables may result in nutritional imbalances or caloric deprivation that could
confound interpretation of the toxicity study results (e.g., lifespan, background rates of tumor incidences) and
alter the outcome and reproducibility of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test article doses than
expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed groups
to compensate for the differences in energy and nutrient content of the high dose diets. Such circumstances
make it especially important that feed consumption of these animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of litter-
mate weanling rats of the same sex and approximate size are selected and fed the control or the experimental
diet. Animals should be single-caged so that feed consumption can be determined daily, and the control
animal is then fed an amount of food equal to that which the paired experimental animal ate on the preceding
day. If the test substance is non-nutritive and composes a significant proportion of the diet, the pair-fed
control animals should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of
diet as the paired experimental animal. Additionally, the study should include a second group of control
animals fed ad libitum to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term and subchronic toxicity studies because of batch to batch variations in diet
composition (e.g., fiber, mineral, vitamins, isoflavones) in some of the commonly used laboratory animal
H. Diet:
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chows. The use of these semi-purified diets, however, may not be advisable in long-term and reproductive
studies due to inadequate historical data related to their influences on animal survival and toxicological
endpoints. For example, loss of necessary but unidentified micronutrients in the semipurified diet may
interfere with normal reproduction.
Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993 draft
"Redbook II".
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day; if this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. If the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
For example, under normal circumstances, mortality in the control group should not exceed 10% in short and
intermediate length (not lifetime) toxicity studies.
Adequate animal husbandry practices should result in considerably less than 10% of animals and tissues or
organs lost to a study because of autolysis. Autolysis in excess of this standard may be cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are as similar as possible in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
I. Assignment of Control and Compound Treated Animals:
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
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Animals should be exposed to the test substance 7 days per week for the designated length of time of the
study.
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (for
example, in soft drinks or beer), or if administration in the diet is inappropriate for other reasons. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size; for rodents, the volume ordinarily should not exceed 1
ml/100 g body weight. If the gavage vehicle is oil (see Chapter IV.B.5.b. in the 1993 draft "Redbook II"),
then the volume should be no more than 0.4 ml/100 g of body weight, and the use of a low-fat diet
should be considered. If the test substance must be given in divided doses, all doses should be
administered within a 6 hour period. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished.
Three to five dose levels of the test substance and concurrent control groups should be used with both males
and females. Information obtained from acute (Chapter IV.C.2. in the 1993 draft "Redbook II") and short-
term (Chapter IV.C.3.a. and b.) toxicity studies can help determine appropriate doses for subchronic studies.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
C. Dose groups:
1. Selection of Treatment Doses:
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Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II. Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in "II. Test Animals, H. Diet" above.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 14
Routine cage-side observations should be made on all animals at least once or twice a day throughout the
study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10.), conducted inside
and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions and autonomic activity (e.g.,
lacrimation, pilorection, pupil size, unusual respiratory pattern). Additionally, changes in gait, posture and
response to handling, as well as the presence of clonic or tonic movements, stereotypes (e.g., excessive
grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should be
recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Recommendations are described in guidelines for specific toxicity study types (see Chapter IV.C. of the 1993
draft "Redbook II" and/or "Redbook 2000"). Feed spillage should be noted and adjustments made in related
calculations and appropriate discussion presented in the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: 	This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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in the study.
2. 	Hematology: 	The recommended number of animals and time intervals for hematology assessment are
found in individual toxicity study guidelines (see Chapter IV.C.3.-5. of "Redbook 2000" and Chapter
IV.C.2. and 6.-8. of the 1993 draft "Redbook II"). Ideally, the same rodents should be sampled at each
collection time point. Blood samples should be analyzed individually, and not pooled. If animals are
sampled on more than one day during a study, blood should be drawn at approximately the same time
each sampling day.
1. 	The following determinations are recommended:
1. 	hematocrit
2. 	hemoglobin concentration
3. 	erythrocyte count
4. 	total and differential leukocyte counts
5. 	mean corpuscular hemoglobin
6. 	mean corpuscular volume
7. 	mean corpuscular hemoglobin concentration
8. 	and a measure of clotting potential (such as clotting time, prothrombin time, thromboplastin
time, or platelet count).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
3. 	Clinical Chemistry: The recommended number of animals and time intervals for clinical chemistry
assessment are found in individual toxicity guidelines (see Chapter IV.C.3.-5. of "Redbook 2000" and
Chapter IV.C.2. and 6.-8. of the 1993 draft "Redbook II"). Ideally, the same rodents should be sampled
at each collection time point. Blood samples should be drawn at the end of the fasting time and before
feeding. Fasting duration should be appropriate for the species and the analytical tests to be performed.
Blood samples should be analyzed individually, and not pooled. If animals are sampled on more than one
day during a study, blood should he drawn at approximately the same time each sampling day.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, carbohydrate metabolism, and liver and kidney function. Specific determinations should
include:
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
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5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
1. 	However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the
test compound may warrant the consideration of alternative tests. Appropriate justification for
alternative tests should be presented in study reports.
1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day15 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: Timed urine volume collection should be conducted during the last week of the study and at
other time intervals described in specific individual toxicity study guidelines (Chapter IV.C.3.-5. of
"Redbook 2000" and Chapter IV.C.2. and 6.-8. of the 1993 draft "Redbook II"). The volume of urine
collected, specific gravity, pH, glucose, and protein should be determined as well as conducting a
microscopic evaluation of urine for sediment and presence of blood/blood cells 16 .
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
short-term and subchronic toxicity studies with rodents (preferably rats) and non-rodents (preferably
dogs), one-year studies in non-rodents, and reproductive toxicity studies in rodents. The neurotoxicity
screen should be age appropriate and would typically include: (1) specific histopathological examination
of tissue samples representative of major areas of the brain, spinal cord, and peripheral nervous system
(see organs and tissues listed below under VI.C. Preparation of Tissues for Microscopic Examination) and
(2) a functional battery of quantifiable observations and manipulative tests selected to detect signs of
neurological, behavioral, and physiological dysfunctions. This functional battery is also referred to as an
expanded set of clinical evaluations and is described more fully in section V.A. Observations of Test
Animals in this Chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Toxicity study reports should include an assessment of the potential for the test substance to adversely
affect the structural or functional integrity of the nervous system. This assessment should evaluate data
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from the neurotoxicity screen and other toxicity data from the study, as appropriate. Based on this
assessment, the petitioner should make an explicit statement about whether or not the test substance
presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed appropriate. FDA
recommends that additional neurotoxicity testing not be undertaken without first consulting with the
Agency.
6. 	Immunotoxicity: For short-term, subchronic and developmental toxicity studies, results of clinical tests
that are included in the list of primary indicators for immune toxicity (see Chapter V.C. of the 1993 draft
"Redbook II") should also be evaluated as part of an immunotoxicity screen. Additional immunotoxicity
tests are discussed in Chapter V.C. of the 1993 draft "Redbook II", but should not be undertaken without
first consulting with the Agency.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
Sponsors should refer to specific studies (Chapter IV.C.1.-10.) for details.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	Harderian gland (if present)
15. 	heart
16. 	ileum
17. 	jejunum
18. 	kidneys
19. 	liver
20. 	lung (with main-stem bronchi)
21. 	lymph nodes (1 related to route of administration and 1 from a distant location)
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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22. 	mammary glands
23. 	nasal turbinates
24. 	ovaries and fallopian tubes
25. 	pancreas
26. 	pituitary
27. 	prostate
28. 	rectum
29. 	salivary gland
30. 	sciatic nerve
31. 	seminal vesicle (if present)
32. 	skeletal muscle
33. 	skin
34. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
35. 	spleen
36. 	stomach
37. 	testes
38. 	thymus (or thymic region)
39. 	thyroid/parathyroid
40. 	trachea
41. 	urinary bladder
42. 	vagina
43. 	Zymbal's gland (if present)
44. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V.C.) for all animals in short-term and subchronic toxicity studies and
developmental toxicity studies.
1. 	EPA Health Effects Test Guidelines OPPTS 870.3050, 28-Day Oral Toxicity in Rodents, July 2000
2. 	EPA Health Effects Test Guidelines OPPTS 870.3150, 90-Day Oral Toxicity in Non-Rodents, August 1998
3. 	EPA Health Effects Test Guidelines OPPTS 870.3100, 90-Day Oral Toxicity in Rodents, August 1998
4. 	EPA Health Effects Test Guidelines OPPTS 870.4100, Chronic Toxicity, August 1998
5. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 90-day Oral Toxicity Study in Non-
Rodents, 409, September 1998
6. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 90-day Oral Toxicity Study in Rodents,
408, September 1998
7. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 28-day Oral Toxicity Study in Rodents,
407, July 1995
8. 	Kurt Weingand et al., 1996. "Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
Studies", Fundamental and Applied Toxicology, 29, pp 198-201.
9. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
10. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995.
11. 	Nutrient Requirements of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
12. 	Nutrient Requirements of Swine: 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
13. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
14. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
15. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
16. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor & Francis, Philadelphia, PA, pp. 520-533
Links on this page:
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
Guidelines for reporting the results of toxicity studies are contained in this section. More complete information
regarding Pathology and Statistics can be found in Chapters IV.B.3. 2 and IV.B.4. 3 , respectively. The study
report should include all information necessary to provide a complete and accurate description and evaluation
of the study procedures and results in accordance with 21 CFR 58.185 4
. The following sections should be
included:
A. 	Study title and report number
B. 	Testing facility by name and address
C. 	Duration of study
D. 	Dates of:
1. 	Acclimation
2. 	Initiation (onset of dosing)
3. 	Sacrifice/termination
4. 	Study report
E. 	Identification and signatures (where appropriate) of personnel primarily responsible for:
1. 	Conduct of the study (i.e., study director, principal investigator)
2. 	Analyses of data
3. 	Histopathology
4. 	Writing the report
5. 	Other information contained in the report
Redbook 2000: IV.B.2 Guidelines for Reporting the Results of Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.B.2. Guidelines for Reporting the Results of Toxicity Studies
I. Study Identification and Information
II. Good Laboratory Practice for Nonclinical Laboratory Studies Statement
Food
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Redbook 2000: IV.B.2 Guidelines for Reporting the Results of Toxicity Studies
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The Good Laboratory Practice (GLP) regulations were designed to establish minimal standards for conduct and
reporting of nonclinical safety testing and are intended to assure the quality and integrity of safety data
submitted to the FDA. Each food and color additive petition, Generally Recognized as Safe (GRAS) affirmation
petition, and Food Contact Notification (FCN) must include a GLP compliance statement as set forth in 21 CFR
171.1(k), 21 CFR 71.1(g), 21 CFR 170.35(c)(1)(vi), or 21 CFR 170.101(c).
Each study report must include a quality assurance statement signed by the quality assurance unit in
accordance with 21 CFR Section 58.35(b)(7) which states: "Prepare and sign a statement to be included with
the final study report which shall specify the dates inspections were made and findings reported to
management and to the study director."
A protocol for each non-clinical study should be written so that it satisfies all GLP requirements set forth in
Section 21 of CFR § 58.120 5 . The protocol should include clearly stated objectives and methods for the
conduct of the study. A copy of the protocol should be attached to the study report. The study report should
include statements describing all changes in or revisions of the protocol, the reasons for those changes, and
any influence these changes had on the results of the study.
This section of the study report should include information regarding the availability and location of original
data, specimens and samples of the test substance, in accordance with 21 CFR 58.190 6 and 195 7 .
This section of the study report should contain a brief description of:
A. 	Methods
B. 	Summary and analysis of numerical data
C. 	Summary and analysis of descriptive data (e.g., observations to assess neurotoxic potential)
D. 	The conclusions drawn from the analyses, including target organ(s) and no observed effect levels
(NOELs)
The summary should highlight all significant changes in data or observations of the test substance
treated groups, in comparison to the control groups, which may be an indication of toxic effects of the
test substance. The summary should also include a description of the relationship between dose and the
incidence/severity of lesions or abnormalities.
The summary should include a description of all circumstances that may have influenced the quality or
integrity of the data or observations.
A. 	Identification
1. 	Chemical name
2. 	Chemical Abstracts Service (CAS) registry number (or code number)
3. 	Molecular structure and molecular weight
4. 	Qualitative and quantitative determination of its chemical composition
B. 	Manufacturing information
1. 	Lot number
2. 	Purity, including names and quantities of known contaminants and impurities and the percentage of
unidentifiable materials
3. 	Expiration date
4. 	Stability
III. Quality Assurance Statement
IV. Protocol and Amendments
V. Storage, Retrieval, and Retention of Records
VI. Summary and Conclusions
VII. Test Substance
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5. 	Storage instructions
C. 	Physical properties
1. 	State (i.e., powder, liquid)
2. 	Color
3. 	Solubility, in aqueous and in dosing vehicle
4. 	pH (pKa where applicable)
5. 	Boiling and melting point
D. 	Identification of diluents, suspending agents, emulsifiers, excipients, or other materials used in
administering the test substance.
E. 	Sampling of test material in administered form
1. 	Times when sampling was performed
2. 	Verification of stability of test compound in administered form: method and results
3. 	Verification of homogeniety of test compound in administered form: method and results
4. 	Verification of concentration of test compound in administered form: method and results
F. 	Storage conditions: during and after the study
A. 	Species and strain (and substrain if applicable) used and, particularly if a strain other than a common
laboratory strain is used in the study, rationale for selection of the strain
B. 	Source or supplier of the animals
C. 	Description of any pre-test conditioning (such as quarantine procedures)
D. 	Description of the method used to randomize animals into test and control groups
E. 	Numbers, age, and condition of animals of each sex in all test substance treated and control groups at
the beginning and end of the study
F. 	Diet
1. 	Feed
a. 	Diet: lot number, composition, etc.
b. 	Availability: i.e., ad libitum
2. 	Water
a. 	Availability: i.e., ad libitum
G. 	Caging conditions
1. 	Number of animals per cage
2. 	Bedding material
3. 	Ambient temperature
4. 	Humidity
5. 	Lighting conditions
The methods section of the study report should include, but not be limited to, the following information
A. 	Deviations from these Redbook 2000 guidelines
1. 	Describe all ways in which the test procedure deviates from these Redbook 2000 guidelines
2. 	State the rationale for each deviation.
B. 	Experimental design and procedures (full description)
VIII. Test Animals
IX. Methods
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1. 	Length of the study (including dates study began and ended)
2. 	Data on dosage administration should include
a. 	All dose levels administered, expressed as mg/kg body weight, per unit of time (e.g. day)
b. 	Route of administration
c. 	Method, frequency, and time of day of administration
d. 	Total volume of dose plus vehicle administered to each animal, if the test substance is
administered by gavage
e. 	Duration of treatment period
3. 	Observation of the test animals
a. 	Duration of individual observation
b. 	Frequency
c. 	Method
4. 	Sampling Conditions of specimens (hematology, clinical chemistry, urinalysis, other)
a. 	Duration and time of day
b. 	Frequency
c. 	Method
5. 	Statistical analyses: All statistical methods used should be fully described or identified by
reference. For a complete discussion of the information that should be contained in this section of
the study report, see Chapter IV.B.4 8 .
A. 	Individual animal data and results should be provided in tabular format and in sufficient detail to permit
independent evaluation of the results. Describe all computerized systems used in the generation,
measurement, or assessment of data including the name and version of the system (software) and the
specified indications for use. The following information should be included for each test animal:
1. 	Time of first observation of each abnormal sign and its subsequent course. These data should be
organized, when appropriate, by litter.
2. 	Time of death during the study. The "most probable" cause of death should also be determined and
reported for those animals that were not sacrificed at the pre-scheduled time.
3. 	Feed and water consumption data (including feed spillage)
4. 	Body weights and body weight changes
5. 	Feed efficiency data
6. 	Hematology, clinical chemistry, urinalysis, and other clinical findings
7. 	Results of neurotoxicity and immunotoxicity studies, as appropriate
8. 	Gross necropsy findings including:
a. 	absolute and relative organ weights
b. 	description of gross lesions
c. 	incidence and severity of gross lesions
9. 	Histopathology findings (see Chapter IV.B.3. 9 ) including:
a. 	description of microscopic lesions
b. 	incidence and severity of microscopic lesions
B. 	Summarized data from individual animals should be organized by sex and dose group and provided in
tabular format. When appropriate, data should also be organized by litter. When numerical means are
presented, they should be accompanied by an appropriate measure of variability, such as the standard
error. For each summarized parameter, the following information should be included:
1. 	The number of animals at the beginning of the study
XI. Results and Discussion
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
4. 	http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/showCFR.cfm?CFRPart=58
5. 	http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/showCFR.cfm?CFRPart=58
6. 	http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/showCFR.cfm?CFRPart=58
7. 	http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/showCFR.cfm?CFRPart=58
8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
9. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
10. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
2. 	The number of animals evaluated for each parameter
3. 	The day of the study (e.g., day 60, at termination) when animals were evaluated for each
parameter
C. 	All numerical results should be evaluated by an appropriate statistical method. Refer to Chapter IV.B.4.
10 for detailed guidelines about statistical considerations in toxicity studies.
D. 	Evaluation of the results should include at a minimum:
1. 	Discussion about the nature of relationships, if any, between exposure to the test substance and
the incidence and severity of all general and specific adverse effects (such as neoplastic and non-
neoplastic lesions, organ weight effects, and mortality effects), and identification of target organs.
2. 	Discussion about the relationship between clinical observations made during the course of a study
and post mortem findings.
3. 	A conclusion statement regarding the dosage level at which no effects attributable to the test
substance were observed (NOEL), and a discussion of any complex and/or any controversial issues
surrounding that determination.
This section of the study report should include appropriate literature citations or references, for the following:
A. 	Test procedures
B. 	Statistical and other methods used to analyze the data
C. 	Compilation and evaluation of results
D. 	The basis upon which conclusions were reached
The above guidance document supersedes the previous version dated October, 2001.
X. References
Links on this page:
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July 2000
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
a. 	Description of the Process for Review of Pathology Data
b. 	Common Problems Encountered During Review of Pathology Data
i. 	Lack of Morphologic Descriptions of Lesions
ii. 	Inconsistency in Applying Diagnostic Terminology
iii. 	Incomplete Descriptions of the Results of Gross Pathology Examinations
iv. 	Inaccurate Summaries of Data
v. 	Failure to Adequately Discuss the Results of Pathology Examinations
c. 	General Recommendations for Reporting Pathology Data
i. 	Arranging Tabular Data and Morphological Observations
ii. 	Summary Tables
iii. 	Cross Reference Table
iv. 	Animal Disposition Table
v. 	Pathologist's Narrative
d. 	Reference
Pathology data make up an essential part of the toxicology information submitted to FDA in support of the
safe use of the use of food ingredients. The interpretation of pathology data and other safety data forms the
basis for judgement about the safety of a product.
Specific recommendations concerning necropsy of test animals and microscopic examination of organs and
tissues for short-term toxicity tests with rodents and non-rodents, subchronic toxicity tests with rodents and
non-rodents, one-year toxicity tests with non-rodents, carcinogenicity studies with rodents, combined chronic
toxicity/carcinogenicity studies with rodents, reproduction studies, and developmental toxicity studies can be
found in Chapter IV.B.1.e. In general, these guidelines recommend that all animals in the studies be subjected
to complete gross necropsy, all gross lesions and all protocol-required tissues and organs (see Chapter
IV.B.1.e.iii.) from all control and high dose animals in the study should be examined microscopically; all gross
lesions and target organs from all other dosed groups should also be examined microscopically.
Redbook 2000: IV.B.3 Pathology Considerations in Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.B.3. Pathology Considerations in Toxicity Studies
Food
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Redbook 2000: IV.B.3 Pathology Considerations in Toxicity Studies
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This section on pathology considerations in toxicity studies describes the review process for pathology data,
identifies common problems reviewers encounter in reviewing such data, and presents general guidelines for
reporting pathology data. Although not addressed in this chapter, CFSAN pathologists also review and provide
advice to petitioners on protocols for proposed toxicity studies; requests for such review should be directed to
the CSO assigned to the petition (see Chapter II.A.).
Review of pathology data may begin with a request for pathology evaluation from regulatory review scientists
or from the CAC. This happens when questions about the interpretation of pathology data arise during the
scientific review of the toxicology information submitted in support of the safety of food ingredients . Requests
for review are generally limited to specific interpretative questions, directing the reviewing pathologist's
attention to findings in a particular organ or tissue. Occasionally, a reviewing pathologist is asked to examine
all of the pathology findings in a study.
The pathology portion of the study report usually contains mean and individual organ weight parameters,
clinical chemistry results, hematological measurements, summary incidences of observed pathological
changes, and gross and microscopic pathology observations for individual animals. An evaluation
memorandum from the regulatory review scientist may accompany the material; the memorandum contains
summaries of toxicology information, including the results of previous toxicity studies and information from
relevant scientific literature.
The reviewing pathologist usually begins his/her review by examining the experimental design and methods.
He/she carefully reviews general indices of toxicity in test animals (for example, body weight gain, food
consumption, clinical or hematologic findings, and organ weight changes); particular attention is paid to the
survival of the animals and the number of animals alive at termination. All this information helps the reviewing
pathologist evaluate the relationship of observed pathology changes to treatment.
Although the approach to pathology review may vary, the elements listed below are considered in all reviews.
The reviewing pathologist:
z Determines how the percentage of animals with lesions in summary incidence tables has been
calculated; for example, was the denominator based on the total number of animals in the study, or was
it the number of animals for which a particular tissue or organ was examined microscopically;
z Compares gross and microscopic findings to ensure that all gross observations are accounted for by
microscopic findings or by other suitable explanations;
z Examines the diagnostic terminology applied to lesions to determine whether it is contemporary and
conventional;
z Checks to see that individual animal data provide adequate information on the location, size, and
distribution of reported gross lesions;
z Considers the qualitative characteristics, severity of lesions, and the incidence figures in evaluating
treatment-related differences among groups of experimental animals;
z Carefully evaluates control data before interpreting findings;
z Evaluates the discussion of significant pathological findings prepared by the study pathologist; and
z Correlates pathology findings, when appropriate, with other observations about treatment-related effects
on test animals during the study.
When the pathology review is completed, a formal written report is submitted to the collaborating regulatory
review scientist. The report discusses the pathological findings based on review of submitted material and the
relationship of pathological findings to treatment. If questions about the pathology data remain, the report
may recommend a request for additional, clarifying material.
A follow-up pathology review requires additional data. The additional information most often requested by the
Agency is clarification of the diagnostic criteria used and historical control data for a specific lesion. The
Agency may ask to review the original microscope slides; in some cases, the petitioner may be asked to
prepare new slides from paraffin blocks or wet tissue for FDA review. The Agency's review of slides from a
toxicity study provides an independent characterization of the lesions and enables the incidence of lesions to
be verified.
When microscope slides and other materials are requested by the Agency for a follow-up review, the Agency
provides instructions for their submission. Usually, microscope slides from an organ or tissue site should be
a. Description of the Process for Review of Pathology Data
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arranged by treatment group, sex, and in the order of pathology accession numbers. If microscope slides are
submitted according to the Agency's directions, the follow-up review will be expedited.
The timely review of pathology data is sometimes hindered by missing, inaccurate, or incomplete information.
These problems are often encountered in submissions to the Agency; a general discussion of problems
resulting from information deficiencies is presented below. A more detailed discussion of this subject has been
published. (1)
One of the most common problems causing delay in the review of pathology data is the lack of adequate
morphologic descriptions of lesions. It is difficult to assess the significance of reported lesions without
information on their diagnostic criteria, distribution, and severity. This is particularly important when the
terminology for lesions is controversial.
The use of multiple diagnostic terms without explanation for describing a single type of lesion can present
problems for the reviewing pathologist. Further clarification is needed to indicate whether two or more terms
are being used interchangeably or the results of the study have been evaluated by more than one pathologist,
each using different terms for the same morphologic change. For example, in one study the terms
"hepatocellular carcinoma" and "hepatoma, malignant" were used in the same set of diagnoses. In another
report, four different terms--"c-cell," "clear cell," "light cell," and "parafollicular cell"--were used to describe
rat thyroid lesions. In both instances, reasons for using multiple terms for the same diagnosis were not
provided.
Differences in the use of diagnostic terms have been encountered when more than one pathologist has
examined slides: for example, a study was submitted in which tissues from about one-third of the animals
were evaluated by the study pathologist and the remainder were evaluated by a consulting pathologist. The
diagnostic terminology was not consistent between pathologists and no attempt was made to explain the
inconsistencies in the study report. Although the data appeared to show treatment-related effects, these were
subsequently attributed to the way different categories of lesions were summarized.
Incomplete gross descriptions have made it difficult to correlate gross pathology findings with microscopic
diagnoses. When microscopic findings do not correlate with gross descriptions, the reviewer must attempt to
determine if important information is missing. The report should describe steps taken to resolve discrepancies
between gross findings and microscopic diagnoses (for example, recuts of paraffin blocks or additional
samples taken from wet tissues).
Inaccurate summary numbers resulting from incorrect counts or calculations have caused difficulty in
reviewing pathology data. When pathology data are summarized, all experimental animals should be
accounted for and incidence figures should be based on the numbers of animals, organs, and tissues actually
examined.
Often, submissions fail to adequately discuss the significance of the results of pathology evaluations. Some
reports summarize conclusions but do not explain how the conclusions were deduced from the available
pathology data. Some reports base conclusions solely on the results of statistical analyses of data, ignoring
broader conclusions that may be discerned from considering all relevant biological information from a study.
b. Common Problems Encountered during Review of Pathology Data
i. Lack of Morphologic Descriptions of Lesions
ii. Inconsistency in Applying Diagnostic Terminology
iii. Incomplete Descriptions of the Results of Gross Pathology Examinations
iv. Inaccurate Summaries of Data
v. Failure to Adequately Discuss the Results of Pathology Examinations
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The pathology section in the report of a toxicity study generally includes an introductory statement and
sections on materials and methods, results and discussion, and summary and conclusions.
When pathology data are reported separately from the toxicity study, adequate information about the
experimental design and methodology of the toxicity study should be included. This information should include
the species and strain of the experimental animals, details about the administration of the test compound,
number of experimental and control groups, number of animals in each group, type and frequency of in-life
observations including clinical chemistry measurements and hematological examinations, and the scope of
gross and microscopic evaluation of tissues. In general, information provided should be sufficient to enable a
reviewer to evaluate the quality of the pathology data.
Deviations from the original protocol should be explained. For example, if tissues from low- and mid-dose
groups were not scheduled for microscopic examination but were examined, the appropriate protocol
amendment or reason for this deviation should be given.
The arrangement of tabular information in an easily comprehensible format is especially important for
facilitating review. Table titles and row and column headings should be brief but informative. In the tables
showing the individual animal findings, descriptive diagnostic categories should be informative. Redundancy of
categories of lesions should be avoided. Morphologic diagnoses should reflect currently accepted criteria.
Whenever multiple categories of lesions are grouped under a common "diagnosis," the rationale for grouping
should be provided. When multiple diagnoses are not grouped under a common diagnosis, it will be assumed
that morphologic differences preclude grouping. Severity grades as well as information on the distribution of a
lesion within an organ or tissue should be provided; these observations are particularly important when
progression of lesions and effects of different dosages are being studied. In paired organs such as adrenal
glands, gonads, and kidneys, certain lesions, when appropriate, should be indicated as unilateral or bilateral.
All gross lesions should be accounted for by microscopic findings or a written explanation.
Summary tables in the results section of a report should clearly indicate the number of animals, organs, and
tissues actually examined. Unless the number of tissues examined in animals of each group is indicated, the
incidence figures or mean values indicating effects are subject to question. Summary tables should be free of
double counting. In determining incidence, the denominators should reflect actual numbers of animals whose
tissues were examined, not just the number of animals originally assigned to each group. The figure for the
number of tissues examined should clearly show any adjustments that reflect loss, autolysis, or missing
tissue: For example, the accurate incidence of lesions involving the adrenal medulla should be based upon
how many adrenal sections (for an animal) from both adrenal glands contained sufficient medullary tissue for
microscopic examination. In summarizing lesions that are disseminated, e.g., tumors of the lymphoreticular
tissue, the incidence figures should reflect the number of animals with these lesions, not just the presence of
the disease in individual organs.
A cross-reference table that lists individual lesions on the vertical axis and individual animal numbers along
the horizontal axis should be included, if possible. This is convenient both for reviewing lesions within an
animal and for comparing lesions across animals in a group or among different groups.
The report should generally contain an animal disposition table that provides the pathology accession number,
sex, group designation, number of days on the study, and fate of the animals (for example, interim sacrifice,
moribund sacrifice, found dead, or terminal sacrifice). This serves as a ready reference for the Agency's
scientific reviewers and eliminates the need to develop this information from individual animal data.
c. General Recommendations for Reporting Pathology Data
i. Arranging Tabular Data and Morphological Observations
ii. Summary Tables
iii. Cross-Reference Table
iv. Animal Disposition Table
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
Finally, the report should include a section that specifically discusses the pathology data. This pathology
narrative should provide an overview of the pathology findings from the study pathologist's perspective. A
discussion that includes qualitative description of lesions and that highlights differences among treated and
control groups is an essential part of the interpretation and evaluation of pathology data. The description of
morphologic characteristics of lesions is particularly important where terminology may be controversial or
misunderstood. Remarks about possible pathogenesis, strengthened by references to the scientific literature,
could be an important part of the pathologist's narrative. Significant events, such as a disease outbreak during
the study, and the impact of such events on the study outcome should be discussed. Differences in the
incidence of key histopathologic findings among groups should be discussed; if observed differences are not
regarded as treatment-related, then the basis for this conclusion should be provided.
1. 	Dua, P.N., and B.A. Jackson (1988). Review of Pathology Data for Regulatory Purposes. Toxicologic
Pathology. 16:443-450.
v. Pathologist's Narrative
d. Reference
Links on this page:
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
a. 	Specific Statistical Issues
i. 	Study Protocol and Design
ii. 	Presentation of Collected Data
iii. 	Presentation and Interpretation of Analytical Results
iv. 	Support from CFSAN Statistical Reviewers
b. 	Statistical Considerations Reference
The regulations governing approval for marketing imply that submissions should contain both statistical
analyses of toxicology data presented in the submission and documentation of the analyses. The purpose of
this section is to guide the submitter in documenting statistical aspects of toxicity studies contained in food
ingredient submissions so that CFSAN reviewers can evaluate these studies efficiently. Additional advice in the
form of Standard Operational Procedures (SOPs) prepared by the Division of Mathematics of CFSAN's Office of
Toxicological Sciences is available upon request from the CSO assigned to the petition.
To ensure the validity of safety assessments of a food ingredient obtained from well-conducted toxicity
studies, statistical expertise should be used routinely in the planning, design, execution, analysis, and
interpretation of results. This guideline highlights factors that are of primary importance in assessing the
validity of evidence from toxicity studies. These factors are 1) study protocol and design, 2) presentation of
collected data (individual animal data), 3) presentation and interpretation of analytical results (including tables
of summary data), and 4) other considerations.
FDA emphasizes that communication between statisticians and the scientists conducting a particular toxicity
study can help ensure that the statistics used are relevant to the biology of the toxicity test. For example,
statistical outliers are not always biological outliers, and a "significant" statistical test (p < 0.05) does not
always indicate biological significance. FDA encourages petitioners to consult with Agency statisticians during
the design and conduct of the study and the interpretation of data from the study, as appropriate.
The following recommendations offer general guidance to the petitioner in organizing and documenting the
results of toxicity studies: (1)
Redbook 2000: IV.B.4 Statistical Considerations in Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.B.4. Statistical Considerations in Toxicity Studies
Food
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Redbook 2000: IV.B.4 Statistical Considerations in Toxicity Studies
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z Data should be submitted in a form that will enable FDA reviewers to easily verify the results by
duplicating the analysis or, if necessary, performing an alternative analysis. The best way to accomplish
this is to submit the data in tabular form in the petition and, at the same time, in a machine-readable
form (see Chapter II.B. for additional information about submission of machine-readable data).
z Summary tables of the data also should be submitted.
z The submission should be organized and documented so as to enable Agency reviewers to move easily
between the data and the summary tables. (For example, if the report of a bioassay involving 50 rats in
a dose group includes a summary table indicating that the incidence of a given tumor is 3/40, there
should be auxiliary tables showing which three rats had the tumor, which 37 rats were examined but did
not have the tumor, and which ten rats were not examined for the tumor.)
z When outliers are removed for statistical reasons, the statistical test upon which the decision to remove
them was based should be specified.
z The description of a statistical inference should include a statement about the model used, summary
data appropriate for the model, analysis of the data with estimates of treatment effects, and reasonable
statistical checks on the adequacy of the model.
z In presenting tables of summary data that reference statistical tests of hypotheses, a statement should
identify the null and alternative hypotheses, the statistical test, the sampling distribution of the test
statistic under the null hypothesis, the value of the test statistic, the degrees of freedom of the test
statistic (when appropriate), the p-value, and whether the test is one or two tailed.
z Statistical analyses should be directly linked to specific questions regarding the safety of the additive
(i.e., comparing results for treated groups with results for a control group and evaluating the effects of
various animal characteristics (sex, species, age, etc.) on the results of an experiment).
z Results of the statistical analyses of all toxicity studies (e.g., p-values, confidence intervals) should be
tabulated. Additionally, an effort should be made to explain how these results contribute to resolving
questions about the safety of the food ingredient .
z The submission should cross-reference related information (e.g., data tabulations, statistical hypotheses
tested, models used, etc.) that will facilitate FDA's statistical review of the study.
The submitted petition should contain the original protocol and a complete account of protocol modifications
made during the course of the study. The protocol is a critical document in the evaluation of a bioassay,
shaping both the conduct of the study and the ultimate analyses. It sets forth the objectives of the study and
relates these objectives to the statistical hypotheses that are tested. It describes critical features of the
study's design and execution, such as the purpose of the study, experimental design (subchronic, short-term,
multi-generation), selection of species, selection of parameters to be assessed, planned interim analyses of
data, planned interim and final sacrifices, events that would trigger early termination of the study, roles and
responsibilities of data monitoring boards or quality assurance boards, and proposed statistical methods. By
designating in advance the treatment groups and the variables that will be considered to be primary endpoints
for statistical analyses, the protocol appropriately defines and limits the hypotheses that the study is able to
test.
A well-designed experimental protocol will normally contain, as a minimum, the following items:
z Statement of objectives: In addition to the primary objective(s), secondary objective(s) should be
stated explicitly. The precise hypotheses that the study is attempting to prove or disprove also should be
stated explicitly.
z Source of test animals: A clear statement about the species, strain, sex and source of the test animals
in the study and how animals are screened from the study (i.e., will "runts" be eliminated; why?).
z Experimental design: This should include information about initial baseline periods (if any), the study
configuration (short-term, lifetime, etc.), the treatment levels, the control group(s), the number of
animals in each group (sample size), and the criteria for terminating the study.
z Randomization procedures: A description of the randomization procedure(s) used to assign animals to
experimental groups. Generally, a computer-driven procedure using a random number generator is
a. Specific Statistical Issues
i. Study protocol and design
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better than a table of random numbers.
z Administration: A statement about the route of administration and frequency of administration of the
test compound.
z Diets: A complete description of any diets used in the study.
z Control of confounding factors: A statement about how the effects of confounding response variables
of interest (i.e., caging effects) were minimized. If this is not possible, that fact should be stated along
with the reason for the inability to discount these effects and the possible impact on the study.
z Experimental parameters measured: A description of the parameters that will be measured and a
statement about how frequently they will be measured.
z Power analysis: If the number of animals being used is within the guidelines given in this publication
for the type of study being planned, a power analysis is not necessary. If fewer numbers of animals are
to be used, then a power analysis or a statement about the differences in study parameters between
compared groups that the study is able to detect should be submitted.
z Quality control: A description of the steps taken to ensure accurate, consistent, and reliable data (e.g.,
standard operating procedures, instruction manuals, data verification).
z Data analysis: A description of planned interim analyses of the data, including monitoring procedures,
variables to be analyzed, statistical analyses to be used (including the choice of significance level for
each interim analysis), and frequency of analysis.
z Statistical Methods: A description of the statistical methods to be applied to the data. Here, specific
questions that the statistical analyses will address in support of the study objectives are identified. For
example, a description of the methodology that would be used to detect outliers may be important. The
major end-points for analysis should be identified. If multiple comparisons are to be made, they should
be pre-planned.
Information on every animal in the study should be presented. Data should be organized so that the reviewer
can easily find all information about any animal used in the study. For example, data should be organized so
that the reviewer can view all study parameters for a single animal and a single parameter for all animals.
Individual animal records can be presented or data can be tabulated, depending on the study and the type of
data collected. The liberal use of data tables and submission of machine-readable data is strongly encouraged
(see contact information 2 for electronic submissions). Steps taken to assure the numerical accuracy of the
collected data should be documented in detail sufficient to permit the reviewer to judge their accuracy.
As described previously, the identifying number, age upon entry into the study, dose level, sex, initial body
weight, and cage identification should be presented for each animal in the study. There also should be a table
showing how animals were randomized into their respective dose groups. Other information should include:
z For each animal, length of time in the study, date of death, type of death (e.g., scheduled sacrifice,
moribund sacrifice, animal found dead, etc.), and reason for early withdrawal from the study, if this
occurred (e.g., escaped from cage).
z Food, water, and test compound consumption at each interval specified in the protocol.
z All measured values for defined parameters and the times at which these measurements were taken. If
deviations from standard operating procedures occurred in taking the measurements, the nature of the
deviation, the reason for the deviation, and its impact on the study should be discussed.
z For all microscopic lesions: a) type of lesions (neoplastic or non-neoplastic) should be clear from the
morphologic diagnosis; b) when appropriate, severity grades (e.g., mild, moderate, marked) for non-
neoplastic lesions should be included; c) when appropriate, modifiers such as "metastatic", "invasive" or
"systemic" should be used for neoplastic lesions; and d) information indicating when the lesion was first
observed (in life or at necropsy) should be included in the individual animal data.
Presentation of results of statistical analysis should include a description of, and rationale for, all statistical
methods used. Unless the method is well-known (e.g., analysis of variance), references should be provided. A
thorough discussion of the statistical analysis, including reasons for the use of a particular analysis,
ii. Presentation of collected data
iii. Presentation and interpretation of analytical results
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assumptions, conduct of the analysis, and validity of the conclusions, will guide FDA in deciding whether re-
analysis of the data is needed. For each analysis of a relevant variable that is submitted, the following
information should be provided:
z Specific variables and analysis of variance: A statement identifying the specific variable; if not
obvious, a discussion of its relevance to the objectives of the study should be included.
z Statistical model: The statistical model underlying the analysis; references should be provided, if
necessary.
z Hypothesis: A statement of the hypothesis being tested and of the alternative hypothesis.
z Power calculation: A power calculation for tests that failed to reject the null hypothesis, particularly to
justify the adequacy of the sample size.
z Confidence intervals: The statistical methods used to estimate effects, construct confidence intervals,
etc.; literature references should be supplied when appropriate.
z Outliers: The methods used to detect outlying data points (outliers) and the reasons why particular
methods were selected. Identified outliers should be studied in an attempt to determine the reason for
their deviation from other data in the set.
z Assumptions underlying the statistical methods: It should be shown that, insofar as is statistically
reasonable, the data satisfy crucial assumptions, especially when such assumptions are necessary to
confirm the validity of an inference. For example, in deciding whether to use parametric or non-
parametric methods, tests for normality and for equality of variances should be conducted.
z Survival analyses: Such analyses will address the question of whether treated animals died earlier than
control animals and will help determine if treated animals lived long enough to enable treatment-related
tumors to be detected.
z Analysis of tumors: Analysis of tumors (benign and malignant) and other lesions for each group of test
animals. Whether the tumor is an incidental finding upon death or a cause of death should dictate the
method of analysis used. The major theoretical difference between these analyses is the manner in
which the number of animals at risk in each time interval is defined. This needs to be taken into account
in performing tests such as the standard Cox Life Table test.
z Trend test: A trend test, when appropriate. This includes not only a test for linearity, but a test for lack
of fit as well.
z Plots or graphs of summary data: Care should be taken to generate plots that will convey the most
information: For example, in studies with many animals in each dose group, it may be better to plot the
mean and confidence limits or plus or minus one (±1) standard deviation than to attempt to plot
individual data.
The following points are also important in the presentation of collected data:
z Transformation of data: Unnecessary data transformations should be avoided. If data transformation
has been performed, a rationale for the transformation and an interpretation of the estimates of
treatment effects based on transformed data should be provided.
z Parametric and non-parametric analyses of data: Parametric and non-parametric analyses of the
same parameter at different time periods should be avoided. For example, if equality of variances in a
parameter measured over time is tested, and some tests turn out significant and others do not, the
statistician should arrive at a consensus (i.e., does the preponderance of evidence point to equality of
variances or not). We recommend that this be done by converting p-values obtained to standard normal
deviates (z-scores) and obtaining the p-value for the average score times the square root of the number
of p-values.
z Litter and caging effects: Litter and caging effects should be taken into account in determining the
statistical model. If this is not possible, that fact should be stated along with the reason for the inability
to account for these effects and its possible impact on the study.
z Repetitive measurements: For parameters that are measured across time, a repeated measures
analysis should be considered.
z Dependent experimental parameters: If a given parameter depends biologically on another
parameter (i.e., organ weight depends on body weight), then the dependent parameter should be
adjusted, as in analysis of co-variance.
z Time of death: Time of death should be reported as days from the start of the study. For example, if a
study began on January 1, 1997 and the animal died on January 1, 1999, then the animal died on Day
Redbook 2000: IV.B.4 Statistical Considerations in Toxicity Studies
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/~dms/opa-help.html
730.
z Reproduction studies: In reproduction studies, if a dam continues in the study after all pups have
died, the number of pups in her litter should be counted as 0.
z Statistical comparisons: When statistical comparisons of data were not pre-planned, a statement on
how bias was avoided in choosing the particular analysis should be included.
z Statistic: The statistic, the sampling distribution of the test statistic under the null hypothesis, the value
of the test statistic, the significance level (i.e., p-value), a statement of whether the test used was one
or two tailed, and intermediate summary data should be presented in a format that will enable the
reviewer to verify the results of the analysis quickly and easily. In most cases, a copy of the computer
output will provide the necessary information. For example, documentation of a two-sample t-test should
include the two sample sizes, the mean and variance for each of the samples, the pooled estimate of
variance, the value of the t-statistic, the associated degrees of freedom, and the p-value.
z Computer programs: When possible, commonly available computer programs should be used; please
consult with FDA statisticians about appropriate programs. If it is necessary to use a program written by
the petitioner itself, the program should be fully documented, including:
{ the source code;
{ test runs against "known" results; that is, textbook examples, examples worked by hand, or
examples run with packaged programs. These test runs should cover every case that could arise in
connection with the data in the petition. Test cases should be run both before and after the
program is used for the submitted data.
In the case of a complex toxicity test or carcinogenicity bioassay, the petitioner is encouraged to consult with
CFSAN before conducting the study or submitting the petition to discuss relevant statistical considerations.
Requests for comments by statistical reviewers on protocols for proposed toxicity studies can be sent to the
CSO assigned to the petition (see Chapter II.A. ).
If unusual concerns arise during the conduct of a study, the petitioner may submit preliminary tabulations of
the data and materials pertaining to the statistical analysis to CFSAN for advice and guidance.
1. 	Dubey, Satya (June, 1985) Draft Guidelines for the Format and Content of the Statistical Sections of an
Application. 	(Return to text)
iv. Support from CFSAN Statistical Reviewers
b. Statistical Considerations Reference
Links on this page:
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Draft
Chapter IV. Guidelines for Toxicity Tests
IV B General Recommendations for Toxicity Studies
IV B 5. Diets for Toxicity Studies
The effects of diet composition on the responses of experimental animals to xenobiotics have been
review ed. 1-6 Some of the most important effects include:
4 Diet composition may influence experimental results through effects on background rates of
toxicology pa ram eters, such as tu m or incidence. 7,8
4 U nre co gn iz ed or in ad eq ua te ly co ntro lle d n utritio na l a nd oth er d ie ta ry va ria ble s m a y a lte r th e o utc om e
and reproducibility of long-term toxicity studies.8
4 A nu mb er of nutrients a nd non -nutritive dieta ry com pone nts have been s how n to enh ance or inhibit
carcinogenesis; these include calories or energy, fat, protein, fiber, vitamins C and E, selenium, and
lipotropes (methionine, choline, folacin, and vitamin B12. Dietary fibers have been shown to reduce,
enhance, or hav e no effe ct on the toxicity a nd c arcinogenicity of chem icals. 9,10 Detailed reviews of the
inte raction s of n utrie nts a nd c arcinogens have be en reporte d. 3,11-15
a. Types of D iets
i. Na tural Ingredie nt Die ts
Natural ingredient diets are the most widely used diets in toxicology research. They are prepared from
unrefined plant an d anim al m aterials suc h as w heat, corn , oats, fish me al, soybea n m eal, or w heat bra n and a re
characterized as open formu la or closed formu la diets. The percen tages of ing redients in o pen form ula diets a re
kno wn, bu t the com pos ition of close d form ula diets is p roprieta ry inform atio n. 16 Natu ral ingredie nt diets sup port
growth and reproduction and are economical, comm ercially available, and satisfactory for studies involving
additiv es th at w ill no t affe ct nutrie nt balances.
Limitations of natural ingredient diets for toxicity studies include:
4 Variations in types and quan tities of nutrients and other dietary com ponents are due to seve ral factors;
for exam ple, the com pos ition of fib ers m ay vary w ith th eir sources, 17 the mineral content of natural
ingredie nt diets ca n vary sig nificantly a mo ng prod uction b atche s, and spe cifications fo r essential d ietary
elem ents are no t alw ays m et. 18
4 Diet composition cannot be altered to study the effects of varying a particular nutrient, which makes
natural ingredient diets poor choices for research protocols in which nutrition may influence outcome.
4 Nutrient excesses well beyond their requirements, and the presence of other non-nutrients substances
in natural ing redient die ts support rap id we ight gain, preg nanc y, and lac tation in ex perim ental an ima ls
and de crease the effe cts of m any xe nob iotic s.
4 Finally, com mo n conta min ants of na tural ingredie nt diets that c an alter the response of laborato ry
anim als to expe rim ental treatm ent inc lude pe sticides an d m ycotoxins. 13,19
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ii. Purified D iets
The use o f purified diets has been recomm ended to avoid som e of the limitations associated with the use
of natural ingredient diets.13,20,21 Purified die ts usually c ontain refine d proteins, ca rbohyd rates, and fat. V itam in
and m ineral m ixtu res including highly purified vita m ins a nd inorganic salts als o are ad ded to purified diets. 16
AIN-76A, the most c om m only used purified diet, 14 was formulated to provide a diet of known composition that
was intended to meet the known nutrient requirements of rodents; it supports growth, reproduction (generally, one
or tw o ge neratio ns), a nd lactatio n in a m anner sim ilar to na tura l ingredient die ts. 16
Advantages of using purified diets for toxicity studies include:
4 Ability to reproduce nutrient concentrations from batch to batch,
to maintain the nutrient composition of a diet within a narrow range, and to alter the type and composition
of dieta ry com pon ents. 20
4 Use of purified diets usually decreases dietary intake of
contaminants such as pesticide residues, heavy metals, enzyme inducers and other agents that may alter
the resp ons es o f test anim als to expe rim ental treatm ent. 14,20,21
Disa dvan tages of u sing purified diets for toxicity stu dies inclu de:
4 Difficulty in a ssessing th e im pact of pu rified diets on a nim al surviva l and toxic ology e ndpoin ts
because adequate historical data regarding the use of such diets is lacking;
4 L ac k o f in fo rm a tio n a bo ut th e su ita bility of p urifie d d ie ts fo r lo ng -te rm stu die s, a lth ou gh so m e
researc hers hav e used purified diets su ccess fully for up to 56 we eks; 22,23
4 Errors that may occur in the preparation of purified diets may be m ore critical than similar errors in the
prepara tion of natu ral ingredie nt diets be cause , in purified diets, eac h ingredie nt m ay be th e sole die tary
sou rce of an es sen tial n utrie nt. 20 In general, practical experiences with purified diets in long-term studies
have not bee n sa tisfa ctory. 7,24-27
b. Issues to Consider when Selecting and Preparing Diets for Animals in Toxicity Studies
The follow ing are important issues to consider w hen selecting diets for animals in toxicity studies:
4 Protein require m ents for m aintenance and growth of laboratory anim als are we ll ch aracterize d, 20 but
this is not true for most nutrients. Nutrient needs 28 and m etabolism of xeno biotics 29,30 cha nge with age.
Hence, the general practice of feeding a single diet throughout the life cycle of experimental animals may
be inap propriate--nu tritional deficien cies m ay occ ur during p hases o f rapid grow th and d evelop me nt in
young anim als and nutrient excess m ay occur in older anim als.
4 Individual ingredients in purified diets may cause problems in long-term studies. For example,
purified diets high in ingredients such as casein and sucrose m ay stick to the hair of rodents and cause
exce ssive groo min g. Purified sug ars as the so le source of carboh ydrates in diets that are low in d ietary
fibe r m ay cau se d iarrh ea, resu lting in problem s of d igestion an d ab sorp tion of other nutrien ts.
4 For rea son s tha t are incom pletely und erstood , anim als may not reproduce w ell w hen fed pu rified diets.
The components in natural ingredient diets that are required to support reproduction have not been
define d.
4 Toxic chemicals in the diet and induced nutrient deficiencies can lead to decreased food intake by
expe rime ntal anim als and re duce d rates of gro wth a nd dev elopm ent. W hen su ch an e ffect is expe cted to
occur in a long-term study, pair-feeding can be used to eliminate differences in food intake among
000051

experimental groups; this is the preferred method for ensuring that differences in energy or nutrient intake
have not cau sed the observed exp erim ental re sults or c om plic ated their in terp reta tion . For exa m ple, a
mod erate restriction of energy intake may increase the life-span, decrease the ba ckground can cer rates,
and de crease the pote ncy of c arcinog ens in rod ents, thereb y poten tially m odulating the action of a
chemical carcinogen. When pair-feeding studies are recommended to eliminate differences in food intake
am ong ex perim ental grou ps, anim als shou ld be sing le-cage d and fo od con sum ption sho uld be c arefully
and accurately determined for each animal in the study.
4 When the test substance is added to the diet, accurate records of food consumption must be maintained
to determine the administered dose and food intake must be equalized across control and experimental
groups of animals. When the test substance is a carbohydrate, protein, or fiber that will be added to the
diet in large quantities, it must replace a dietary ingredient or the nutrient and energy contents of the diet
will be significantly diluted (see Chapter VII B 1). The nutrient and energy contents of control diets also
must be adjusted to match those of experimental diets. One recomme nded strategy is to make the control
and test diets isocaloric. If food consumption among groups of experimental animals has been equalized,
then eq ual densities of m etabolizable ene rgy in the diets will eq ualize nutrien t inta ke across the groups . 31
4 W hen oil is used as the gavage vehicle for fat-soluble test substances, the necessity of including a
vehicle-c ontrol group in the stud y m ay intro duc e so m e problem s. 32 If the quantity of oil administered
daily by gavage contributes significantly to the total dietary energy of the animals, results for
experimental and vehicle-control groups may be significantly different than results for the untreated
control group. If a decision is ma de to adm inister a test substance by gavage, the volum e of oil given as a
vehicle should be limited to 0.3 to 0.4 ml/100 g of body weight and the use of a low-fat diet should be
consid ered.
4 Related issues are discussed in the following chapters: 1) control diets for test animals in Cha pter IV
B 1 b-c; 2) survivorship and rec om me ndation s concerning the duration o f carcinog enicity bio assays in
Chapter IV C 6 a; and 3) nutritional concerns for food substitutes (macro-additives) in Cha pter V II B.
References
1. Belinsky, S.A., Kauffman, F.C., and Thursman, R.G. (1987) Effect of nutrition on monooxygenation and
conjugation in the liv er. In, Nutritional toxicology. (J.N. Hathcock, ed.) Academic Press. Orlando, FL.
pp.41-61.
2. Clayson , D.B . (197 5) N utrition and exp erim ental c arcinogenesis: A review . Cancer Res. 35:3292-3300.
3. Co nner, M .W . and N ew berne, P .M. (198 4) Drug -nutrient intera ctions an d their im plications for safety
evaluatio ns. Fund.Appl.Toxicol. 4:S341-S356.
4. M eydani, M . (198 7) D ieta ry effec ts on detoxifica tion processes. In, Nutritional toxicology. (J.N.
Hatchcock ed .) Academ ic P ress . Orlando, F L. 2:1-39.
5. Natio nal Rese arch C oun cil (1 982 ) In, Diet, nutrition, and cancer. National Academy Press. Washington,
D.C.
6. Parke, D.V . and Ioannides, C . (198 1) T he role of nu trition in toxicology. Ann.Rev.Nutr. 1:207-234.
7. Mitchell, G.V., Dua, P.N., Jenkins, M.Y., Grundel, E., and Arzadon, J.M. (1987) The effect of
modifications of the AIN-76A diet on selected nutritional parameters and the incidence of pathology.
Fed.Am.Soc.Exp.Biol. 46:915.
8. Rad er, J.I. (1989) Considerations in designing and using standardized diets in toxicological expe riments.
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In, Nutritional toxicology. (J.N . Ha thcock ed .) Academ ic P ress . Orlando, F L. 3:123-139.
9. Kritch evsky , D., W eber, M .M ., Bu ck, C.L ., and Klurfe ld, D .M . (198 6) C alories, fat and c ancer. Lipids
21:272-274.
10. Om aye, S.T. (1 986 ) Effects of diet on toxicity testing. Fed.Amer.Soc. Exp.Biol. 45:133-135.
11. Ip, C . (198 7) Fat and e ssentia l fatty ac id in mam m ary carcinoge nesis. Am.J.Clin.Nutr. 45:218-224.
12. Kritchevsky, D. (1985) Influence of dietary fiber on xenobiotics. In, Xenobiotic metabolism: Nutritional
effects. Am eric an Chem ical So ciety [A CS]. ACS Sym. Series No. 277.
13. Ne wb erne, P.M . and R ogers, A .E. (1986) L abile m ethyl grou ps and the prom otion of ca ncer.
Ann.Rev.Nutr. 6:407-32.
14. Rao, G.N . (198 8) R ode nt diets for carcinogenesis studies. J.Nutr. 118:929-931.
15. Reddy, B.S., Cohne, L.A., McC oy, G.D., Hill, P., W eisburger, J.H., and Snyder, E.L. (1980) Nutrition
and its rela tion ship to cancer. Adv. Cancer Res. 32:237-345.
16. Am erican Institute of Nutrition (1977) Report of the American Institute of Nutrition Ad Hoc Com mittee
on S tandards fo r Nutritional S tudies. J.Nutr. 107:1340-1348.
17. W ise, A. and Gilbu rt, D.J. (1980) Th e variab ility of dietary fibre in la boratory a nim al diets an d its
rele vance to the con trol o f experim ental c ond ition s. Fd.Cosmet.Toxicol. 18:643-648.
18. Rader, J.I., W olnik, K.A., Gaston, C.M., Celesk, E.M., Peeler, J.T., Fox, M.R.S., and Fricke, F.L. (1984)
Trace elem ent studies in w eanlin g rats: M aternal die ts an d ba seline tissu e m ineral values. J.Nutr.
114:1946-1954.
19. Fox, J.G ., Aldric h, F.D., a nd B oylen, G.W . (197 6) L ead in animal foods . J.Toxicol.Environ. Health 1:461-
467.
20. Natio nal Rese arch C oun cil (1 978 ) In, The nutrient requ irem ents of labo ratory anim als. No. 10, 3rd
revised ed ition . Na tion al A cadem y of Science Pre ss. W ash ington, D.C .
21. Ro ss, R.H ., Ryon, M .G., Dau gherty, M .W ., Drury, J.S., and En simin ger, J.T. (1980) S cientific ration ale
for th e se lection of toxicity te sting m ethods . In, Hum an Health Assessment. National Technical
Inform atio n Service. Spring field , VA .
22. Crus e, J.P., Lew in, M.R ., Ferulano,G .P., and C larl, C.G. (197 8) Co -carcino genic e ffects of dietary
cholesterol in exp erim ental c olon ca ncer. Nature 276:822-825
23. Cruse, J.P., Lewin, M.R., and Clark, C.G. (1978) Failure of bran to protect against experimental colon
cancer in rats. Lancet 2:1278-1279.
24. Hamm, T.E., Raynor, T., and Caviston, T. (1982) Unsuitability of the AIN-76 diet for male F-344 and CD
rats and im provem ent by substitu ting starch for su crose. Lab. Animal Sci. 32:414-415.
25. Nguy en, H.T . and W ood ard, T.C . (198 0) Intran ephronic calculosis in ra ts. Am.J.Path. 100:39-56.
26. Harwood, E.J. (1982) The influence of dietary magnesium on reduction of nephrocalcinosis in rats fed
purified diet. Lab. Animal Sci. 16:314-318
27. M edinsk y, M .A., Popp, J.A ., Ham m, T .E., and D ent, J.G. (1982 ) Dev elopm ent of hep atic lesion s in m ale
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Fischer-3 44 rats fed AIN-76A purified diet. Toxicol.Appl.Pharmacol. 62:111-120.
28. M unro, H .N. (1 985 ) Nutrie nt needs a nd n utritional status in re latio n to aging. Dru g-Nutrient Interact.
4:55-74.
29. Garattini, S. (1985 ) Drug metabolism and actions in th e ag ed. Drug-Nutrient Interact. 4:87-97.
30. W ellin g, P. (198 5) N utrie nt effec ts on drug m etabolism and action in the elderly. Dru g-Nutrient Interact.
4:173-207.
31. Le veille, G .A. a nd C loutier, P .F. (1987 ) Isoc aloric diets: Effects of dietary cha nge s. Am .J.Clin.Nutr.
45:158-163.
32. Nutrition Found atio n (1983 ) In, Report of the Ad Hoc W orking Group on Oil/Gavage in Toxicology. The
Nutrition Found atio n. W ash ington, D.C .
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
Genetic changes known to be associated with adverse human health effects include gene mutations,
chromosomal rearrangements or deletions, and loss or gain of whole chromosomes (aneuploidy) or
chromosomal segments. Genotoxicity tests are in vitro and in vivo tests designed to detect compounds that
induce genetic damage. Such tests include: (1) tests that directly assess the key types of genetic alterations
(gene mutations and chromosomal effects) and (2) indirect genotoxicity tests that respond to types of DNA
damage known to lead to these alterations. The latter category of tests may assess either DNA damage (e.g.,
DNA adducts or DNA strand breakage) or cellular responses to DNA damage (e.g., unscheduled DNA
synthesis).
FDA recommends the use of a battery of short-term genetic toxicity tests for all when the cumulative
estimated dietary intake exceeds 1.5 μg per person per day, corresponding to 0.5 parts per billion (ppb) in the
total diet. The recommended tests directly measure gene mutations and/or chromosomal effects. The Agency
uses such data, in the absence of long-term animal feeding studies, to determine whether or not a chemical
should be considered to be a possible carcinogen. Such data may also indicate whether a chemical may have
adverse heritable effects. When long-term animal feeding studies are available for the evaluation of
carcinogenicity, genetic toxicity data may assist in the interpretation of the results of such studies.
We consider it essential that chemicals be evaluated for their ability to induce both gene mutations and
chromosomal aberrations. The most widely used test for gene mutations is performed using bacteria as the
target cells. Tests for chemicals that induce gene mutations can also be performed in mammalian cells grown
in vitro. Tests that detect the induction of chromosomal aberrations are performed using cells exposed to
chemicals in vitro or in vivo. While the recommended battery consists of specific genetic toxicity tests, data
from other systems that measure gene mutations, chromosomal effects, DNA damage, or cellular responses to
DNA damage may be relevant to the overall genotoxicity evaluation of a chemical. Therefore, all available data
relating to such endpoints in any test system should be submitted.
The recommended genetic toxicity test battery for food ingredients whose cumulative estimated daily intake
exceeds 50 ppb in the diet (150 μg per person per day) generally includes:
a. 	a test for gene mutations in bacteria 2
Redbook 2000: IV.C.1 Short-Term Tests for Genetic Toxicity
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.1. Short-Term Tests for Genetic Toxicity
Genetic Toxicity Test Battery
Recommended Tests
Food
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Redbook 2000: IV.C.1 Short-Term Tests for Genetic Toxicity
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and
b. 	an in vitro test with cytogenetic evaluation of chromosomal damage using mammalian cells 3
or
an in vitro mouse lymphoma thymidine kinase +/- gene mutation assay 4
(the mouse lymphoma assay is preferred)
and
c. 	an in vivo test for chromosomal damage using mammalian hematopoietic cells 5
.
The Agency prefers the mouse lymphoma tk+/- assay in item "b" because this assay measures heritable
genetic damage arising by several mechanisms in living cells and is capable of detecting chemicals that induce
either gene mutations or heritable chromosomal events, including genetic events associated with
carcinogenesis. In performing the mouse lymphoma tk +/- assay, either the soft agar or the microwell method
is acceptable.
When the cumulative estimated daily intake of a food ingredient is 50 ppb or less but greater than 0.5 ppb,
then the recommended genetic toxicity test battery generally includes items "a" and "b" in the above list since
there are few chemicals that are uniquely genotoxic when tested in vivo for chromosomal damage.
Guidance for performing a test for gene mutations in bacteria 6 and an in vivo micronucleus assay 7 (which is
an acceptable in vivo test for chromosomal damage using mammalian hematopoietic cells) is presented here.
This guidance is based directly on the guidelines published by the Organization for Economic Cooperation and
Development 8 (OECD) or those published by the United States Environmental Protection Agency 9 (US EPA),
which are virtually identical to each other. The reports of the International Conference on Ha rmonisation of
Technical Requirements for Registration of Pharmaceuticals for Human Use 10 (ICH) were used as the basis for
the general recommendations for genetic toxicity testing and were also referred to in drafting the guidelines
on specific test systems. The guidance for an in vivo test for chromosomal damage using mammalian
hematopoietic cells (micronucleus assay) was also based on the report of the 1998 International Workshop on
Genotoxicity Test Procedures (Hayashi, et al., Environmental and Molecular Mutagenesis, 2000, in press). The
FDA has modified these previous guidelines as appropriate. For specific guidance on the conduct of
genotoxicity tests for which guidance is not included here, the above referenced ICH, OECD, or US EPA
guidelines should be consulted.
The mutation assays specified in the standard battery are capable of detecting different spectra of genetic
damage. The tests for gene mutations in bacteria detect point mutations which involve substitution, addition,
or deletion of one or a few DNA base pairs. Point mutations may also be detected in in vitro mammalian cell
mutagenicity assays. The mouse lymphoma tk+/- assay specified in the battery also detects large deletions,
translocations, mitotic recombination/gene conversion and aneuploidy in addition to point mutations, making
this the assay with the broadest spectrum of detectable genetic damage in the battery. The in vitro test with
cytogenetic evaluation of chromosomal damage using mammalian cells detects structural chromosomal
aberrations. The in vivo tests for chromosomal damage using mammalian hematopoietic cells detect structural
chromosomal aberrations in the case of the mammalian bone marrow chromosome aberration test and
structural damage to chromosomes or damage to the mitotic apparatus in the case of the mammalian
erythrocyte micronucleus test.
It should also be noted that, although the mouse lymphoma tk+/- assay and the in vitro test with cytogenetic
evaluation of chromosomal damage using mammalian cells both detect structural chromosomal damage, the
mouse lymphoma tk+/- assay detects damage that is heritable but not lethal to the cells, while the in vitro test
with cytogenetic evaluation of chromosomal damage detects additional types of damage that are lethal to the
cells. Additionally, the mouse lymphoma tk +/- assay is the only assay in the battery capable of detecting gene
conversion/mitotic recombination.
Thus, the tests included in the battery were chosen to complement each other in terms of the specific types of
genetic damage detected. It is not expected that chemicals will always give uniformly positive or negative
results in the various assays. A chemical may, for example, be positive only in the bacterial mutagenicity
assay. Such a result may, nevertheless, be relevant to potential human health effects, including
carcinogenicity. Conversely, it has been shown that some chemicals are negative in the bacterial assay but
positive in other assays. These chemicals are likely operating by mechanisms that cause chromosomal
mutations (large deletions, translocations, gene conversion/mitotic recombination and/or aneuploidy), while
the bacterial assay detects only point and other very small-scale gene mutations.
Types of Genetic Damage
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In addition to the mouse lymphoma tk+/- assay, other in vitro mammalian gene mutation assays, which
employ other cell lines including the CHO, AS52 and V79 lines of Chinese hamster cells and the TK6 human
lymphoblastoid cells, are sometimes used. In these cell lines the most commonly used genetic endpoints
measure mutation at either hypoxanthine-guanine phosphoribosyl transferase (hprt), a transgene of xanthine-
guanine phosphoribosyl transferase (xprt), or thymidine kinase (tk). The tk, hprt, and xprt mutation tests
detect different spectra of genetic events. Differences in sequences in the genes will lead to different spectra
of point mutations that can be detected. In addition, the autosomal location of tk and xprt genes appears to
allow for the detection of genetic events (e.g., chromosomal exchange events) that are not detected at the
hprt locus on the X-chromosome. This is because genetic damage that involves essential genes adjacent to
the hprt locus on the X-chromosome will likely be lethal to the cell, while damage to essential genes on an
autosome will be compensated for by intact genes on the homologous chromosome (which lacks functional tk
or xprt). Also, the lack of a homologous chromosome in the case of the hprt gene may preclude mutations
that arise via homologous recombination. The tk locus in mouse lymphoma cells (the mouse lymphoma tk+/-
assay) is the preferred target for mammalian cell genotoxicity assays because of the wealth of data which
exists to support this locus and assay and because of the broad spectrum of damage detected at this locus.
There are circumstances where the performance of the bacterial reverse mutation test does not provide
sufficient information for the assessment of genotoxicity. This may be the case for compounds that are highly
toxic to bacteria (e.g., some antibiotics) and compounds thought or known to interfere with mammalian cell-
specific systems (e.g., topoisomerase inhibitors, nucleoside analogues, or certain inhibitors of DNA
metabolism). In these cases, usually two in vitro mammalian cell tests should be performed using two
different cell types and two different endpoints, i.e., gene mutation and chromosomal damage. Test
approaches currently accepted for the assessment of mammalian cell gene mutation include tests for
mutation: 1) at the tk locus using mouse lymphoma L5178Y cells or human lymphoblastoid TK6 cells; 2) at
the hprt locus using CHO cells, V79 cells, or L5178Y cells; or 3) at the gpt locus using AS52 cells. When such
additional tests are performed because of the high level of toxicity of the test chemical to bacteria, it is still
important to perform the bacterial reverse mutation test because some antibacterial agents, albeit highly toxic
to the tester strains, are genotoxic at very low, sub-lethal concentrations in the bacterial reverse mutation
test (e.g., nitrofuran antibiotics).
Structurally alerting compounds are usually detectable in the standard test battery. However, compounds
bearing structural alerts that have given negative results in the standard test battery may necessitate limited
additional testing. The choice of additional test(s) or protocol modification(s) depends on the chemical nature,
the known reactivity and metabolism data on the structurally alerting compound under question. For some
classes of compounds with specific structural alerts, it is established that protocol modifications/additional
tests are necessary for optimum detection of genotoxicity (e.g., molecules containing an azo-group requiring
testing of azo reduction products, glycosides requiring testing of hydrolysis products, compounds such as
nitroimidazoles requiring nitroreduction for activation, compounds such as phenacetin requiring another
rodent S9 for metabolic activation). When the standard test battery gives negative results with a chemical
that falls within a class known to require special test conditions, then additional testing with appropriate test
modifications should be performed.
There are compounds for which standard in vivo tests do not provide additional useful information. This
includes compounds for which data from studies on toxicokinetics or pharmacokinetics indicate that they are
not systemically absorbed and therefore are not available for the target tissues in standard in vivo
genotoxicity tests. In cases where sufficient target tissue exposure cannot be achieved, it may be appropriate
to base the evaluation only on in vitro testing.
Additional genotoxicity testing in appropriate models may be conducted for food ingredients that were
negative in the standard test battery but which have shown effects in carcinogenicity bioassay(s) with no clear
evidence for a non-genotoxic mechanism. To help understand the mechanism of action, additional testing can
Modifications of the Test Battery
a. Limited Effectiveness of Bacterial Tests
b. Compounds bearing structural alerts for genotoxic activity
c. Limitations to the use of standard in vivo tests
d. Evidence for tumor response
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078330.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078332.htm
4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078336.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078338.htm
6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078330.htm
7. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078338.htm
8. 	http://www.oecd.org/
9. 	http://www.epa.gov/
10. 	http://www.ifpma.org/
include modified conditions for metabolic activation in in vitro tests or can include in vivo tests measuring
genetic damage in target organs of tumor induction (e.g., liver UDS test, 32 P-postlabelling, mutation induction
in transgenes, or molecular characterization of genetic changes in tumor-related genes).
On rare occasions, a completely novel compound in a unique structural chemical class will be introduced.
When such a compound will not be tested in chronic rodent carcinogenicity bioassays, more extensive
genotoxicity evaluation may be indicated.
e. Structurally unique chemical classes
Links on this page:
Redbook 2000: IV.C.1 Short-Term Tests for Genetic Toxicity
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Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
A. 	The bacterial reverse mutation test uses amino acid-requiring strains of Salmonella typhimurium (S.
typhimurium) and Escherichia coli (E. coli) to detect point mutations, which involve substitution, addition
or deletion of one or a few DNA base pairs.(3),(9),(16) The principle of this bacterial reverse mutation test
is that it detects chemicals that induce mutations which revert mutations present in the tester strains
and restore the functional capability of the bacteria to synthesize an essential amino acid. The revertant
bacteria are detected by their ability to grow in the absence of the amino acid required by the parent
tester strain.
B. 	Point mutations are the cause of many human genetic diseases and there is substantial evidence that
point mutations in oncogenes and tumor suppressor genes of somatic cells are involved in tumor
formation in humans and experimental animals. The bacterial reverse mutation test is rapid, inexpensive
and relatively easy to perform. Many of the tester strains have several features that make them more
sensitive for the detection of mutations, including responsive DNA sequences at the reversion sites,
increased cell permeability to large molecules and elimination of DNA repair systems or enhancement of
error-prone DNA repair processes. The specificity of the tester strains can provide some useful
information on the types of mutations that are induced by genotoxic agents. A very large data base of
results for a wide variety of chemical structures is available for bacterial reverse mutation tests and well-
established procedures have been developed for testing chemicals with different physicochemical
properties, including volatile compounds.
Reverse mutation test in either Salmonella typhimurium or Escherichia coli detects mutation in an amino
acid requiring strain (histidine or tryptophan, respectively) to produce a strain whose growth is independent of
an outside supply of the amino acid.
Point mutations are changes in one or a small number of base pairs in a DNA sequence. Point mutations
may result from base pair substitutions or from small insertions or deletions.
Base pair substitution mutagens are agents that cause a base change in DNA. In a reversion test this
change may occur at the site of the original mutation, or at a second site in the bacterial genome.
Frameshift mutagens are agents that cause the addition or deletion of one or more base pairs in the DNA,
thus changing the reading frame in the RNA.
Redbook 2000: IV.C.1.a Bacterial Reverse Mutation Test
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.1.a. Bacterial Reverse Mutation Test
I. Purpose
II. Definitions
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.1.a Bacterial Reverse Mutation Test
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A. 	The bacterial reverse mutation test utilizes prokaryotic cells, which differ from mammalian cells in such
factors as uptake, metabolism, chromosome structure and DNA repair processes. Tests conducted in
vitro generally require the use of an exogenous source of metabolic activation. In vitro metabolic
activation systems cannot mimic entirely the mammalian in vivo conditions. The test therefore does not
provide direct information on the mutagenic and carcinogenic potency of a substance in mammals.
B. 	The bacterial reverse mutation test is commonly employed as an initial screen for genotoxic activity and,
in particular, for point mutation-inducing activity. An extensive data base has demonstrated that many
chemicals that are positive in this test also are genotoxic in other tests. There are examples of
mutagenic agents which are not detected by this test; reasons for this shortcoming can be ascribed to
the specific nature of the endpoint detected, differences in metabolic activation, or differences in
bioavailability.
C. 	There are circumstances in which the bacterial reverse mutation test may not provide sufficient
information for the assessment of genotoxicity. This may be the case for compounds that are excessively
toxic to bacteria (e.g., some antibiotics) and compounds thought or known to interfere with the
mammalian cell replication system (e.g., topoisomerase inhibitors, nucleoside analogues, or inhibitors of
DNA metabolism). For these cases, usually two in vitro mammalian cell tests should be performed using
two different cell types and two different endpoints, i.e., gene mutation and chromosomal damage (as
discussed in section a. under "Modifications of Test Battery," in IV.C.1. 2
). Nevertheless, it is still
important to perform the bacterial reverse mutation test.
D. 	Although most compounds that are positive in this test are mammalian carcinogens, the correlation is
not absolute; it varies with chemical class. There are carcinogens that are not detected by this test
because they act through other, presumably nongenotoxic mechanisms or mechanisms absent in
bacterial cells or fail because of inadequate metabolic activation.
1. 	Bacterial mutagenicity tests are generally conducted using one of two basic methods. In both of these
procedures, bacterial cultures are exposed to the test substance in the presence and in the absence of
an exogenous metabolic activation system. In the plate incorporation method, (3),(9),(14),(16) these
components are combined in molten overlay agar and plated immediately onto minimal agar medium. In
the preincubation method, (2),(8),(9),(16),(18),(34) the treatment mixture is incubated and then mixed with
the overlay agar before plating onto minimal agar medium. For both techniques, after 2 or 3 days of
incubation, revertant colonies are counted and compared to the number of spontaneous revertant
colonies on solvent control plates.
2. 	Several procedures for performing the bacterial reverse mutation test have been described in addition to
the plate incorporation method and the preincubation method. These additional procedures include the
fluctuation method, (10),(12) and the suspension method. (31) Suggestions for procedures for the testing of
gases or vapors have also been described. (4)
3. 	The procedures described in this document pertain primarily to the plate incorporation and preincubation
methods. Either method is acceptable for conducting experiments both with and without metabolic
activation, although some compounds may be detected more efficiently using the preincubation method.
These compounds belong to chemical classes that include short chain aliphatic nitrosamines, divalent
metals, aldehydes, azo dyes and diazo compounds, pyrollizidine alkaloids, allyl compounds and nitro
compounds. (9) It is also recognized that certain classes of mutagens are not always detected using
standard procedures such as the plate incorporation method or preincubation method. These should be
regarded as "special cases" and it is strongly recommended that alternative procedures be used for their
detection. The following "special cases" could be identified (together with literature citations describing
examples of procedures that could be used for their detection): azo dyes and diazo compounds,(9),(18),
(26),(34) gases and volatile chemicals,(4),(13),(21),(28),(35) and glycosides. (5),(20),(23),(30) Deviations from
standard procedures need to be scientifically justified. In the cases of azo compounds (which are
reduced in the intestine to free aromatic amines) and glycosides (which are hydrolyzed in the intestine
to a sugar and an aglycone), it is preferable to test the free aromatic amine or aglycone metabolites, if
available, by standard techniques rather than using the modified methods in the references cited above.
4. 	There are cases in which test substances derived from plant or animal tissues may contain amino acids
(histidine in the case of the S. typhimurium tester strains and tryptophan for the E. coli WP2 strains), or
III. Initial Considerations
IV. Test Method
A. Principle
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peptides that can serve as a source of these amino acids, at levels that interfere with the conduct of
these standard mutation assay procedures. (1),(27) While there are alternative bacterial mutagenicity
testing procedures that are not affected by the presence of amino acids in test samples (e.g., see
references(11),(22),(24),(29) ), such procedures have not been standardized, widely used, and well
validated. If a test substance derived from biological material causes an increase in mutant colonies in a
bacterial mutagenicity test, the possibility that such an increase may be due solely to the presence of
histidine or tryptophan in the test substance should be evaluated. Experiments designed for such an
evaluation might involve, for example, the testing of amino acid-free extracts of the test substance, with
appropriate controls to show that the procedures used are capable of detecting mutagens added to the
test substance.
a. 	Bacteria
i. 	Fresh cultures of bacteria should be grown up to the late exponential or early stationary phase of
growth (approximately 10 9 cells per ml). Cultures in late stationary phase should not be used.
Excessive aeration of overnight cultures should be avoided. It has been recommended that
overnight shaking of cultures in flasks not exceed 120 rpm.(16) The cultures used in the experiment
should contain a high titer of viable bacteria. The titer may be demonstrated either from historical
control data on growth curves, or in each assay through the determination of viable cell numbers
by a plating experiment.
ii. 	The culture temperature should be 37°C.
iii. 	At least five strains of bacteria should be used. These should include four strains of S. typhimurium
(TA1535; TA1537 or TA97a or TA97; TA98; and TA100) that have been shown to be reliable and
reproducibly responsive among laboratories. These four S. typhimurium strains have GC base pairs
at the primary reversion site and it is known that they may not detect certain oxidizing mutagens,
crosslinking agents and hydrazines. Such substances may be detected by E. coli WP2 strains or S.
typhimurium TA102 (33) which have an AT base pair at the primary reversion site. Therefore the
recommended combination of strains is:
„ S. typhimurium TA1535
„ S. typhimurium TA1537 or TA97 or TA97a
„ S. typhimurium TA98
„ S. typhimurium TA100
„ E. coli WP2 uvrA, or E. coli WP2 uvrA (pKM101), or S. typhimurium TA102.
If there is reason to believe that the test substance may be a crosslinking mutagen, then the test
battery should include strain TA102, or a DNA repair-proficient strain of E. coli (e.g., E. coli WP2 or
E. coli WP2 (pKM101)) should be added.
iv. 	Established procedures for stock culture preparation, marker verification and storage should be
used. The amino acid requirement for growth should be demonstrated for each frozen stock culture
preparation (histidine for S. typhimurium strains, and tryptophan for E. coli strains). Other
phenotypic characteristics should be similarly checked, namely: the presence or absence of R-
factor plasmids where appropriate (i.e., ampicillin resistance in strains TA98, TA100, TA97a, TA97,
and WP2 uvrA (pKM101), and ampicillin + tetracycline resistance in strain TA102); the presence of
characteristic mutations (i.e., rfa mutation in S. typhimurium through sensitivity to crystal violet,
and uvrA mutation in E. coli or uvrB mutation in S. typhimurium, through sensitivity to ultraviolet
light). (9),(16) The strains should also yield spontaneous revertant colony counts within the
frequency ranges expected from the laboratory's historical control data and preferably within the
range reported in the literature.
b. 	Medium
An appropriate minimal agar (e.g., containing Vogel-Bonner minimal medium E and glucose) and an
overlay agar containing histidine and biotin (for S. typhimurium) or tryptophan (for E. coli), to allow for
a few cell divisions, should be used.(3),(10),(16)
c. 	Metabolic Activation
B. Description
1. Preparations
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Bacteria should be exposed to the test substance both in the presence and absence of an appropriate
metabolic activation system. The most commonly used system is a cofactor-supplemented post-
mitochondrial fraction (S9) prepared from the livers of rodents (usually rats) treated with enzyme-
inducing agents such as Aroclor 1254(3),(16) or a combination of phenobarbitone and beta-
naphthoflavone. (7),(19),(25),(30) The post-mitochondrial supernatant fraction is usually used at
concentrations in the range from 10 to 30 percent v/v in the S9 mix. The choice and concentration of a
metabolic activation system may depend upon the class of chemical being tested. In some cases it may
be appropriate to utilize more than one concentration of post-mitochondrial fraction. For azo dyes and
diazo compounds, using a reductive metabolic activation system may be more appropriate.(18),(26)
Liver S9 should be prepared using aseptic techniques so that subsequent filter-sterilization is not
required. Filtration of the S9 or S9 mix may lead to loss of enzyme activity. (16) Each batch of S9,
whether produced by the testing laboratory or obtained commercially, should be tested for sterility and
discarded if contaminated.
d. 	Test Substance/Preparation
Solid test substances should be dissolved or suspended in appropriate solvents or vehicles and diluted as
appropriate prior to treatment of the bacteria. Liquid test substances may be added directly to the test
systems and/or diluted prior to treatment. Fresh preparations should be employed unless stability data
demonstrate the acceptability of storage.
a. 	Solvent/Vehicle
The solvent/vehicle should not be suspected of chemical reaction with the test substance and the
concentration used should be compatible with the survival of the bacteria and the S9 activity. (17) If other
than well-established solvent/vehicles are used, their inclusion should be supported by data indicating
their compatibility. It is recommended that wherever appropriate, an aqueous solvent/vehicle be used.
When testing water-unstable substances, the organic solvents used should be free of water.
b. 	Exposure Concentrations
i. 	Among the criteria to be taken into consideration when determining the highest amount of test
substance to be used are cytotoxicity and solubility in the final treatment mixture. It may be useful
to determine toxicity and insolubility in a preliminary experiment. Cytotoxicity may be detected by
a reduction in the number of revertant colonies or by a clearing or diminution of the background
lawn. However, preliminary toxicity tests in which survival of cells in diluted cultures is determined
may give erroneous results. (32) The cytotoxicity of a substance may be altered in the presence of
metabolic activation systems.
If the doses of the test substance are limited by toxicity, then toxicity should be evident in all
preliminary and final assays at one or more doses, and no toxicity should be evident at three or
more doses in each assay, in each bacterial strain, both with and without metabolic activation.
Insolubility should be assessed as precipitation in the final mixture under the actual test conditions
and evident to the unaided eye in the tube or on the plate. The recommended maximum test
concentration for soluble noncytotoxic substances is 5 mg/plate or 5 μl/plate. For noncytotoxic
substances that are not soluble at 5 mg/plate or 5 μl/plate, one or more concentrations tested
should be insoluble in the final treatment mixture. Test substances that are cytotoxic below 5
mg/plate or 5 μl/plate should be tested up to a cytotoxic concentration. If precipitate is present on
any of the plates, it may interfere with automatic counting of the colonies. In such a situation, all
plates in that series of doses and controls should be counted by hand.
In some cases, toxic levels of a test chemical may kill almost all the cells but permit those that
survive to utilize the histidine in the medium and to grow into visible colonies, even though they
have not undergone mutations from histidine-requiring (His- ) to histidine-independent (His +
) or, in
the case of E. coli, from tryptophan-requiring (Trp -
) to tryptophan independent (Trp +
). This
phenomenon may result in an increase in colony counts at one or more toxic doses although the
chemical may not be mutagenic. In such cases, careful observation of the plates will usually reveal
a clear or almost clear background lawn and unusually small "pinpoint" colonies resulting from
toxicity. When the nature of such colonies remains in question, representative colonies from the
plates of interest can be streaked onto minimal agar plates (supplemented with biotin (for
Salmonella) but not histidine or tryptophan); colonies from solvent control plates are also streaked
2. Test Conditions
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as controls. If the cells streaked from the questionable plates do not grow into colonies and those
streaked from the solvent control plates do grow, then it can be concluded that the questionable
colonies seen were made up of His- (or Trp - ) cells and that the increase in colony counts is not an
indication of mutagenicity of the test chemical. If the cells do grow, this demonstrates that they
were mutants and that the chemical is mutagenic.
ii. 	At least five different analyzable concentrations of the test substance should be used with
approximately half log (i.e., 10) intervals between test points for an initial experiment. Smaller
intervals may be appropriate when a concentration-response is being investigated.
iii. 	Testing above the concentration of 5 mg/plate or 5 μl/plate may be considered when evaluating
substances containing substantial amounts of potentially mutagenic impurities.
c. 	Controls
i. 	Concurrent negative (solvent or vehicle) and strain-specific positive controls, both with and without
metabolic activation, should be included in each assay. Positive control chemicals and
concentrations that demonstrate the effective performance of each assay should be selected.
ii. 	For assays employing a metabolic activation system, the positive control reference substance(s)
should be selected on the basis of the type of bacteria strains used. The following chemicals are
examples of suitable positive controls for assays with metabolic activation:
iii. 	For assays performed without metabolic activation system, examples of strain-specific positive
controls are:
iv. 	Other appropriate positive control reference substances may be used. The use of chemical class-
related positive control chemicals may be considered, when available.
v. 	Negative controls, consisting of solvent or vehicle alone, without test substance, and otherwise
treated in the same way as the treatment groups, should be included. In addition, untreated
controls should also be used unless there are historical control data demonstrating that no
deleterious or mutagenic effects are induced by the chosen solvent.
Chemical 	CAS Number
9,10-Dimethylanthracene 	781-43-1
7,12-Dimethylbenzanthracene 	57-97-6
Congo Red (for the reductive metabolic activation method) 	573-58-0
Benzo(a)pyrene 	50-32-8
2-Acetamidofluorene 	53-96-3
Cyclophosphamide (monohydrate) 	50-18-0 (6055-19-2)
2-Aminoanthracene* 	613-13-8
*2-Aminoanthracene should not be used as the sole indicator of the efficacy of the S9 mix. If 2-
aminoanthracene is used, each batch of S9 should also be characterized with a mutagen that
requires metabolic activation by microsomal enzymes, e.g., benzo(a)pyrene,
dimethylbenzanthracene.
Chemical 	CAS Number 	Strain
Sodium azide 	26628-22-8 	TA1535 and TA100
Nitrofurantoin 	67-20-9 	TA100
2-Nitrofluorene or 4-nitro- 1,2-
phenylenediamine
607-57-8 or
99-56-9 TA 98
9-Aminoacridine or ICR 191 90-45-9 or 17070-
45-0 TA1537, TA97 and TA97a
Cumene hydroperoxide 	80-15-9 	TA102
Mitomycin C 	50-07-7 	WP2 uvrA and TA102
N-Methyl-N'-nitro- N-nitrosoguanidine or
4-nitroquinoline 1-oxide
70-25-7 or
56-57-5
WP2, WP2 uvrA and WP2 uvrA
(pKM101)
Furylfuramide (AF-2) 	3688-53-7 	Plasmid-containing strains
C. Procedure
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a. 	For the plate incorporation method,(3),(9),(14),(16) without metabolic activation, usually 0.05 ml or 0.1 ml
of the test solutions and 0.1 ml of fresh bacterial culture (containing approximately 108 viable cells) are
mixed with 2.0 ml of overlay agar (0.5 ml of sterile buffer may also be included). For the assay with
metabolic activation, usually 0.5 ml of metabolic activation mixture containing an adequate amount of
post-mitochondrial fraction (in the range from 10 to 30 percent v/v in the metabolic activation mixture)
are mixed with the overlay agar (2.0 ml), together with the bacteria and test substance/test solution.
The contents of each tube are mixed and poured over the surface of a minimal agar plate. The overlay
agar is allowed to solidify before incubation.
b. 	For the preincubation method, (9),(16),(18),(34) the test substance/test solution (usually 0.05 ml or 0.1
ml) is preincubated with the tester strain (0.1 ml, containing approximately 10 8 viable cells) and sterile
buffer (0.5 ml) or the metabolic activation system (0.5 ml) usually for 20 min. or more at 30-37°C prior
to mixing with the overlay agar (2.0 ml) and pouring onto the surface of a minimal agar plate. Tubes are
usually aerated during preincubation by using a shaker.
c. 	For an adequate estimate of variation, triplicate plating should be used at each dose level. The use of
duplicate plating is acceptable when scientifically justified. The occasional loss of a plate does not
necessarily invalidate the assay.
d. 	Gaseous or volatile substances should be tested by appropriate methods, such as in sealed vessels. (4),
(13),(28),(35)
All plates in a given assay should be incubated at 37°C for 2 or 3 days. After the incubation period, the
number of revertant colonies per plate is counted.
1. 	Data should be presented as the number of revertant colonies per plate. The number of revertant
colonies on both negative (solvent control, and untreated control if used) and positive control plates
should also be given.
2. 	Individual plate counts, the mean number of revertant colonies per plate and the standard deviation
should be presented for each dose of the test substance and positive and negative (untreated and/or
solvent) controls.
3. 	There is no need to verify a clear positive response. Marginally or weakly positive results should be
verified by additional testing. An attempt should be made to clarify repeatedly equivocal results by
further testing using a modification of experimental conditions. Study parameters that might be modified
include the concentration spacing, the method of treatment (plate incorporation or liquid preincubation),
and metabolic activation conditions such as the mammalian source species for the S9 or the
concentration of S9 in the S9 mix. Nevertheless, it is recognized that results may remain equivocal or
questionable even after repeat testing with modified protocols.
The results of a range-finding test may supply sufficient data to provide reassurance that a reported
clearly negative result is correct. Preliminary range-finding tests performed on all bacterial strains, with
and without metabolic activation, with appropriate positive and negative controls, and with quantification
of mutants, may be considered a sufficient replication of a subsequent complete test whose results are
clearly negative. Alternatively, if negative results are to be confirmed by additional complete testing,
modification of protocols, as described above for repeats of equivocal tests, is recommended.
1. 	There are several criteria for determining a positive result, such as a concentration-related increase over
the range tested and/or a reproducible increase at one or more concentrations in the number of
revertant colonies per plate in at least one strain with or without metabolic activation system.(6)
Biological relevance of the results should be considered first. Statistical methods may be used as an aid
in evaluating the test results. (15) However, statistical significance should not be the only determining
factor for a positive response.
2. 	A test substance for which the results do not meet the above criteria is considered nonmutagenic in this
1. Treatment with Test Substance
2. Incubation
V. Data and Reporting
A. Treatment of Results
B. Evaluation and Interpretation of Results
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test.
3. 	Although most experiments will give clearly positive or negative results, in rare cases the data set will
preclude making a definite judgement about the activity of the test substance. Results may remain
equivocal or questionable regardless of the number of times the experiment is repeated.
4. 	Positive results from the bacterial reverse mutation test indicate that a substance induces point
mutations by base substitutions and/or frameshifts in the genome of either Salmonella typhimurium
and/or Escherichia coli. Negative results indicate that under the test conditions, the test substance is not
mutagenic in the tested species.
The test report should include the following information:
z Identification data, including name and CAS no., if known.
z Physical nature and purity.
z Physicochemical properties relevant to the conduct of the study.
z Stability of the test substance, if known.
z Justification for choice of solvent/vehicle.
z Solubility and stability of the test substance in solvent/vehicle, if known.
z Times dosing solutions were prepared and used (or interval between preparation and usage), and
storage conditions.
z Data that verify the concentration of the dosing solution, if available.
z Strains used.
z Number of cells per culture.
z Strain characteristics.
z Amount of test substance per plate (μg/plate, mg/plate, or μl/plate) with rationale for selection of dose
and number of plates per concentration.
z Media used.
z Source, type and composition of metabolic activation system, including concentration of S9 in S9 mix
and acceptability criteria.
z Treatment procedures.
z Signs of toxicity.
z Signs of precipitation.
z Individual plate counts.
z The mean number of revertant colonies per plate and standard deviation.
z Dose-response relationship, where possible.
z Statistical analyses, if any.
z Concurrent negative (solvent/vehicle) and positive control data, with ranges, means and standard
deviations.
C. Test Report
1. Test Substance
2. Solvent/Vehicle
3. Dosing Solutions
4. Strains
5. Test Conditions
6. Results
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z Historical negative (solvent/vehicle) and positive control data, with e.g., ranges, means and standard
deviations.
The following references should be consulted for additional background information on this test guideline.
1. 	Aeschbacher, H.U., Finot, P.A., and Wolleb, U. (1983) Interactions of histidine-containing test
substances and extraction methods with the Ames mutagenicity test. Mutation Res. 113:103-116.
2. 	Aeschbacher, H.U., Wolleb, U., and Porchet, L.J. (1987) Liquid Preincubation Mutagenicity Test for
Foods. Food Safety 8:167-177.
3. 	Ames, B.N., McCann, J., and Yamasaki, E. (1975) Methods for Detecting Carcinogens and Mutagens
With the Salmonella/Mammalian-Microsome Mutagenicity Test. Mutation Research 31:347-364.
4. 	Araki, A. et al. (1994) Improved Method for Mutagenicity Testing of Gaseous Compounds by Using a
Gas Sampling Bag. Mutation Research 307:335-344.
5. 	Brown, J.P. and Dietrich, P.S. (1979) Mutagenicity of plant flavonols in the Salmonella/mammalian
microsome test. Activation of flavonol glycosides by mixed glycosidases from rat cecal bacteria and other
sources. Mutation Res. 66:223-240.
6. 	Claxton, L.D. et al. (1987) Guide for the Salmonella typhimurium/Mammalian Microsome Tests for
Bacterial Mutagenicity. Mutation Research 189:83-91.
7. 	Elliott, B.M. et al. (1992) Alternatives to Aroclor 1254-Induced S9 in In Vitro Genotoxicity Assays.
Mutagenesis 7:175-177.
8. 	Gatehouse, D.G. et al. Bacterial Mutation Assays. (Ed). Kirkland, D.J. Basic Mutagenicity Tests. UKEMS
Part 1 Revised. (Cambridge University Press, 1990) pp. 13-61.
9. 	Gatehouse, D. et al. (1994) Recommendations for the Performance of Bacterial Mutation Assays.
Mutation Research 312:217-233.
10. 	Green, M.H.L., Muriel, W.J., and Bridges, B.A. (1976) Use of a Simplified Fluctuation Test to Detect Low
Levels of Mutagens. Mutation Research 38:33-42.
11. 	Hera, C. and Pueyo, C. (1986) Conditions for the optimal use of the L-arabinose-resistance mutagenesis
test with Salmonella typhimurium. Mutagenesis 1:267-273.
12. 	Hubbard, S.A. et al. The Fluctuation Test in Bacteria. (Ed). Kilbey, B.J., Legator, M., Nichols, W., and
Ramel C. Handbook of Mutagenicity Test Procedures. 2nd Edition. (Elsevier, Amsterdam-New York-
Oxford, 1984) pp. 141-161.
13. 	Hughes, T.J. et al. (1987) Vaporization Technique to Measure Mutagenic Activity of Volatile Organic
Chemicals in the Ames/Salmonella Assay. Environmental Mutagenesis 9:421-441.
14. 	Kier, L.D. et al. (1986) The Salmonella typhimurium/Mammalian Microsomal Assay: A Report of the U.S.
Environmental Protection Agency Gene-Tox Program. Mutation Research 168:69-240.
15. 	Mahon, G.A.T. et al. Analysis of Data from Microbial Colony Assays. UKEMS Sub-Committee on
Guidelines for Mutagenicity Testing Part II. (Ed). Kirkland, D.J. Statistical Evaluation of Mutagenicity Test
Data. (Cambridge University Press, 1989) pp. 28-65.
16. 	Maron, D.M. and Ames, B.N. (1983) Revised Methods for the Salmonella Mutagenicity Test. Mutation
Research 113:173-215.
17. 	Maron, D., Katzenellenbogen, J., and Ames, B.N. (1981) Compatibility of Organic Solvents With the
Salmonella/Microsome Test. Mutation Research 88:343-350.
18. 	Matsushima, M. et al. Factors Modulating Mutagenicity Microbial Tests. (Ed). Norpoth, K.H. and Garner,
R.C. Short-Term Test Systems for Detecting Carcinogens. (Springer, Berlin-Heidelberg-New York, 1980)
pp. 273-285.
19. 	Matsushima, T. et al. A Safe Substitute for Polychlorinated Biphenyls as an Inducer of Metabolic
Activation Systems. (Ed). F.J. de Serres et al. In Vitro Metabolic Activation in Mutagenesis Testing.
(Elsevier, North Holland, 1976) pp. 85-88.
20. 	Matsushima, T. et al. (1979) Mutagenicity of the Naturally Occurring Carcinogen Cycasin and Synthetic
Methylazoxy Methane Conjugates in Salmonella typhimurium. Cancer Research 39:3780 3782.
7. Discussion of the results.
8. Conclusion.
VI. References
Redbook 2000: IV.C.1.a Bacterial Reverse Mutation Test
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078321.htm
21. 	McGregor, D.B., Reynolds, D.M., and E. Zeiger (1989) Conditions affecting the mutagenicity of
trichloroethylene in Salmonella. Environ. Molec. Mutagenesis 13:197-202.
22. 	Mitchell, I. deG. (1978) Microbial assays for mutagenicity: A modified liquid culture method compared
with the agar plate system for precision and sensitivity. Mutation Res. 54:1-16.
23. 	Nagao, M., Morita, N., Yahagi, T., Shimizu, M., Kuroyanagi, M., Fukuoka, M., Yoshihira, K., Natori, S.,
Fujino, T., and Sugimura, T. (1981) Mutagenicities of 61 flavonoids and 11 related compounds. Environ.
Mutagenesis 3:401-419.
24. 	Nylund, L. and Einsistö, P. (1993) Mutagenicity testing of protein-containing and biological samples
using the Ames/Salmonella plate incorporation test and the fluctuation test. Mutation Res. 272:205-214.
25. 	Ong, T., Mukhtar, M., Wolf, C.R., and Zeiger, E. (1980) Differential effects of cytochrome P450-inducers
on promutagen activation capabilities and enzymatic activities of S-9 from rat liver. J. Environ. Pathol.
Toxicol. 4:55-65.
26. 	Prival, M.J. et al. (1984) Mutagenicity of Benzidine and Benzidine-Congener Dyes and Selected Monoazo
Dyes in a Modified Salmonella Assay. Mutation Research 136:33-47.
27. 	Prival, M.J., Simmon, V.F., and Mortelmans, K.E. (1991) Bacterial mutagenicity testing of 49 food
ingredients gives very few positive results. Mutation Res. 260:321-329.
28. 	Simmon, V., Kauhanen, K., and Tardiff, R.G. Mutagenic Activity of Chemicals Identified in Drinking
Water. (Ed). Scott, D., Bridges, B., and Sobels, F. Progress in Genetic Toxicology. (Elsevier, Amsterdam,
1977) pp. 249-258.
29. 	Skopek, T.R., Liber, H.L., Krolewski, J.J., and Thilly, W.G. (1978) Quantitative forward mutation assay
in Salmonella typhimurium using 8-azaguanine resistance as a genetic marker. Proc. Natl. Acad. Sci.
U.S.A. 75:410-414.
30. 	Tamura, G. et al. (1980) Fecalase: A Model for Activation of Dietary Glycosides to Mutagens by
Intestinal Flora. Proceedings of the National Academy of Sciences USA 77:4961-4965.
31. 	Thompson, E.D. and Melampy, P.J. (1981) An Examination of the Quantitative Suspension Assay for
Mutagenesis With Strains of Salmonella typhimurium. Environmental Mutagenesis 3:453-465.
32. 	Waleh, N.S., Rapport, S.J., and Mortelmans, K.E. (1982) Development of a toxicity test to be coupled to
the Ames Salmonella assay and the method of construction of the required strains. Mutation Res.
97:247-256.
33. 	Wilcox, P. et al. (1990) Comparison of Salmonella typhimurium TA 102 With Escherichia coli WP2 Tester
Strains. Mutagenesis 5:285-291.
34. 	Yahagi, T. et al. (1975) Mutagenicity of Carcinogen Azo Dyes and Their Derivatives. Cancer Letters
1:91-96.
35. 	Zeiger, E. et al. (1992) Salmonella Mutagenicity Tests. V. Results from the Testing of 311 Chemicals.
Environmental and Molecular Mutagenesis 19:2-141.
Links on this page:
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Introduction
II. 	Good Laboratory Practice
III. 	Definitions
IV. 	Initial Considerations
V. 	Principle of the Test Method
VI. 	Description of the Method
VII. 	Data and Reporting
VIII. 	References
The purpose of the in vitro chromosomal aberration test is to identify agents that cause structural
chromosomal aberrations in cultured mammalian cells 1, 2, 3
. Structural aberrations may be of two types,
chromosome or chromatid. With the majority of chemical mutagens, induced aberrations are of the chromatid
type, but chromosome type aberrations also occur. The in vitro chromosomal aberration test may employ
cultures of established cell lines, cell strains or primary cell cultures. Chromosomal aberrations are the cause
of many human genetic diseases and there is substantial evidence that chromosomal damage and related
events causing alterations in oncogenes and tumor suppressor genes of somatic cells are involved in cancer
induction in humans and experimental animals.
An increase in polyploidy may indicate that a chemical has the potential to induce numerical aberrations 25 .
However, the protocol prescribed in this guidance document is not intended to provide an adequate method
for the detection of agents that cause numerical chromosomal aberrations. Thus, a lack of polyploidy should
not be considered adequate evidence that the test material does not have the potential to induce numerical
aberrations, including aneuploidy.
This guidance document is based on the guidelines published by the Organization for Economic Cooperation
and Development (OECD) and/or those published by the United States Environmental Protection Agency (US
EPA). At the date of publication of this chapter, these documents are available at:
Redbook 2000: IV.C.1.b In vitro Mammalian Chromosomal Aberration Test
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.1.b. In vitro Mammalian Chromosomal Aberration Test
I. Introduction
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.1.b In vitro Mammalian Chromosomal Aberration Test
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http://www.oecd.org 2 and http://www.epa.gov/ 3
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Aneuploid: Having an abnormal number of chromosomes not an exact multiple of the haploid number.
Centromere: A region(s) of a chromosome with which spindle fibers are associated during cell division,
allowing orderly movement of daughter chromosomes to the poles of the daughter cells.
Chromatid-type aberration: Structural chromosomal damage expressed as breakage of single chromatids
or breakage and reunion between chromatids.
Chromosome-type aberration: Structural chromosomal damage expressed as breakage, or breakage and
reunion, of both chromatids at an identical site.
Clastogen: An agent that induces chromosome breaks, an essential step in the formation of structural
chromosomal aberrations.
Endoreduplication: A process in which after the S phase of DNA replication, the nucleus does not go into
mitosis but starts another S phase. The result is chromosomes with 4, 8, 16,...chromatids.
Gap: An achromatic lesion smaller than the width of one chromatid, and with minimum misalignment of the
chromatid(s).
Mitotic index: The ratio of cells in metaphase divided by the total number of cells observed in a population of
cells; an indication of the degree of proliferation of that population.
Numerical aberration: A change in the number of chromosomes from the normal number characteristic of
the cells utilized.
Polyploidy: A multiple of the haploid chromosome number (n) greater than the diploid number (i.e., 3n, 4n
and so on).
Structural aberration: A change in chromosomal structure detectable by microscopic examination of the
metaphase stage of cell division, observed as intrachanges, or interchanges, or deletions and fragments.
Tests conducted in vitro generally require the use of an exogenous source of metabolic activation. This
metabolic activation system cannot mimic entirely the mammalian in vivo metabolic and pharmacokinetic
conditions. Care should be taken to avoid extreme conditions of pH or osmolality which would lead to positive
results which do not reflect intrinsic mutagenicity 4, 5
.
This test is used to screen for possible mammalian mutagens and carcinogens. Many compounds that are
positive in this test are mammalian carcinogens; however, correlation is dependent on chemical class and
there is increasing evidence that there are carcinogens that are not detected by this test or other genetic
toxicity tests because they appear to act through mechanisms other than direct DNA damage.
Cell cultures are exposed to the test substance both with and without metabolic activation. At predetermined
intervals after exposure of cell cultures to the test substance, they are treated with a metaphase-arresting
substance (e.g., Colcemid® or colchicine), harvested, stained and metaphase cells are analyzed
microscopically for the presence of chromosomal aberrations.
II. Good Laboratory Practice
III. Definitions
IV. Initial Considerations
V. Principle of the Test Method
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A variety of mammalian cell lines, strains or primary cell cultures, including human cells, may be used (e.g.,
Chinese hamster fibroblasts, human or other mammalian peripheral blood lymphocytes). Cells are selected for
use in the assay on the basis of experience with the cell type, growth ability in culture, stability of the
karyotype, chromosome number, chromosomal morphological diversity, and spontaneous frequency of
chromosomal aberrations. Established cell lines and strains should be checked routinely for stability in the
modal chromosome number.
Appropriate culture media, and incubation conditions (culture vessels, CO2 concentration, temperature and
humidity) should be used in maintaining cultures. Cultures should be monitored routinely for the absence of
mycoplasma contamination and should not be used if contaminated. The normal cell cycle time for the cells
and culture conditions used should be known.
Established cell lines and strains: cells are propagated from stock cultures, seeded in an appropriate culture
medium at a density such that the cultures will not reach confluency before the time of harvest, and incubated
at 37°C.
Lymphocytes: whole blood treated with an anti-coagulant (e.g., heparin) or separated lymphocytes are added
to an appropriate culture medium containing a mitogen (e.g., phytohemagglutinin) and incubated at 37°C.
Lymphocytes from different individuals may respond differently to culture conditions or the test materials.
Therefore, lymphocytes from at least two healthy donors should be used.
Solid test substances should be dissolved or suspended in appropriate solvents or vehicles and diluted if
appropriate prior to treatment of the cells. Liquid test substances may be added directly to the test systems
and/or diluted prior to treatment. The volume of the test material plus solvent or vehicle should be the same
in all cultures, including negative and vehicle controls. Fresh preparations of the test substance should be
employed unless stability data demonstrate the acceptability of storage.
The solvent/vehicle should not interfere in any way with the performance of the test, e.g., by reacting
chemically with the test substance, by affecting the metabolism of the test substance by S9, by altering the
response of the cell to the test substance, or by inducing changes in the cell. The suitability of non-standard
vehicles/solvents must be demonstrated according to these criteria. It is recommended that wherever
possible, the use of an aqueous solvent/vehicle be considered first. When testing water-unstable substances,
the organic solvents used should be free of water. Water can be removed by adding a molecular sieve.
Cells should be exposed to the test substance both in the presence and absence of an appropriate metabolic
activation system. The most commonly used system is a co-factor-supplemented post-mitochondrial fraction
(S9) prepared from the livers of rats treated with enzyme-inducing agents such as Aroclor 1254 6, 7, 8, 9
, or a
mixture of phenobarbitone and ß-naphthoflavone 10, 11, 12 . The post-mitochondrial fraction is usually used at
concentrations in the range from 1-10% v/v in the final test medium. The condition of a metabolic activation
system may depend upon the class of chemical being tested. In some cases it may be appropriate to utilize
more than one concentration of post-mitochondrial fraction. A number of developments, including the
construction of genetically engineered cell lines expressing specific activating enzymes, may provide the
potential for endogenous activation. The prudent use of engineered cell lines in place of exogenous metabolic
activation should be scientifically justified (e.g., by the relevance of the cytochrome P450 isoenzyme for the
metabolism of the test substance).
VI. Description of the Method
A. Preparations
1. Cells
2. Media and Culture Conditions
3. Preparation of Cultures
4. Preparation of Doses
B. Test Conditions
1. Solvent/Vehicle
2. Metabolic Activation
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Concurrent positive and negative (solvent or vehicle) controls both with and without metabolic activation
should be included in each experiment.
Positive controls should employ a known clastogen at exposure levels expected to give a reproducible and
detectable increase over background which demonstrates the sensitivity of the test system. Positive control
concentrations should be chosen so that the effects are clear but do not immediately reveal the identity of the
coded positive control slide to the reader. When metabolic activation is used, the positive control chemical
should be the one that requires activation to give a clastogenic response. Examples of positive control
substances include:
*There are literature reports (compiled in reference 26) showing that, in some studies but not in others,
cyclophosphamide can be clastogenic in vitro in the absence of metabolic activation. If cyclophosphamide is
used as a positive control, it should also be tested in the absence of S9 to demonstrate its S9-dependence in
the cell line being used in that laboratory.
Among the criteria to be considered when determining the highest concentration are cytotoxicity, solubility in
the test system, and changes in pH or osmolality.
It may be useful to determine cytotoxicity and solubility in a preliminary dose-range finding assay using the
same treatment regimen and metabolic activation to be used in the definitive chromosomal aberration study.
Cytotoxicity should be determined using an appropriate indication of cell integrity and growth, such as degree
of confluency, viable cell counts, plating efficiency, or mitotic index. Cytotoxicity should also be determined
with and without metabolic activation in the definitive assay.
Analyzable cells must be obtained from a minimum of three test concentrations. Where cytotoxicity occurs,
these concentrations should cover a range from the maximum to little or no toxicity; this will usually mean
that the concentrations should be separated by no more than a factor between 2 and the square root of 10. At
the time of harvesting, the highest concentration should show a reduction in degree of confluency, cell count,
or plating efficiency, of at least 50%. The use of mitotic index as a measure of cytotoxicity is acceptable for
mixed cell cultures, such as whole blood cultures where peripheral lymphocytes are used as the genotoxic
target cell. In these types of cultures other toxicity estimators are not possible or are technically impractical. A
reduction in mitotic index can indicate a cytostatic rather than cytotoxic response and may be affected by the
length of time between treatment and harvest. It is therefore not recommended as a measure of cytotoxicity
in experiments with cell lines in which other measures of cytotoxicity are possible. Information on cell cycle
kinetics, such as average generation time (AGT), could be used as supplementary information. AGT, however,
is an overall average that does not always reveal the existence of delayed subpopulations, and even slight
increases in average generation time can be associated with very substantial delay in the time of optimal yield
of aberrations.
For relatively non-cytotoxic compounds the maximum concentration should be 5 μl/ml, 5 mg/ml, or 0.01M,
whichever is the lowest.
For relatively insoluble substances that are not toxic at soluble concentrations, the highest dose tested should
be a concentration above the limit of solubility in the culture medium at the end of the treatment period. It
has been suggested that in some cases (e.g., when toxicity occurs only at insoluble concentrations) it may be
advisable to test at more than one concentration with visible precipitation. In considering this
recommendation, caution should be exercised to minimize conditions that complicate quantification of results.
It may be useful to assess solubility at the beginning and the end of the treatment, as solubility can change
during the course of exposure in the test system due to presence of cells, S9, serum etc. Insolubility can be
detected by using the unaided eye. The precipitate should not interfere with the scoring.
3. Controls
Metabolic activation condition 	Chemical and CAS No.
Absence of exogenous metabolic
activation
Methyl methanesulfonate [CAS no. 66-27-3]
Ethyl methanesulfonate [CAS no. 62-50-0]
Ethylnitrosourea [CAS no. 759-73-9]
Mitomycin C [CAS no. 56-57-7]
4-Nitroquinoline-N-Oxide [CAS no. 56-57-5]
Presence of exogenous metabolic
activation
Benzo(a)pyrene [CAS no. 50-32-8]
Cyclophosphamide (monohydrate)* [CAS no. 50-18-0 (CAS no.
6055-19-2)]
4. Dose Levels
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In some cases, it may be possible to use lower chemical concentrations and to increase the treatment time
(without metabolic activation) so that the test can be performed under conditions where the chemical is
soluble. Fresh chemical preparations should be employed unless stability data demonstrate the acceptability of
storage.
Proliferating cells are treated with the test substance in the presence and absence of a metabolic activation
system. Treatment of lymphocytes should commence at about 48 hours after mitogenic stimulation.
Duplicate cultures should normally be used at each concentration, and are strongly recommended for
negative/solvent control cultures. Where minimal variation between duplicate cultures can be demonstrated
13, 14 from historical data, it may be acceptable for single cultures to be used at each concentration.
Gaseous or volatile substances should be tested by appropriate methods, such as in sealed culture vessels 15,
16 .
In the first experiment, cells should be exposed to the test substance both with and without metabolic
activation for 3-6 hours, and sampled at a time equivalent to about 1.5 normal cell cycle length after the
beginning of treatment 12 . If this protocol gives negative results both with and without activation, an
additional experiment without activation should be done, with continuous treatment until sampling at a time
equivalent to about 1.5 normal cell cycle lengths. Certain chemicals may be more readily detected by
treatment/sampling times longer than 1.5 cycle lengths12 . Negative results with metabolic activation need to
be confirmed by additional testing. Modification of the test protocol, such as variation of S9 source or
concentration, should be considered for this confirmatory test.
Cell cultures are treated with Colcemid® or colchicine usually for one to three hours prior to harvesting. Each
cell culture is harvested and processed separately for the preparation of chromosomes. Chromosome
preparation involves hypotonic treatment of the cells, fixation and staining 27 . Hypotonic treatment should be
adjusted to provide optimal separation of chromosomes but without loss of chromosomes. Staining should
allow accurate discrimination of chromosome structures 27 .
All slides, including those of positive and negative controls, should be independently coded before microscopic
analysis. Since fixation procedures often result in the disruption of a proportion of metaphase cells with loss of
chromosomes, the cells scored should contain a number of centromeres equal to the modal number ± 2 for all
cell types. At least 200 well-spread metaphases should be scored per concentration and control equally
divided among the duplicates, if applicable. This number can be reduced when high numbers of aberrations
are observed. Though the purpose of the test is to detect structural chromosomal aberrations, it is important
to record polyploidy and endoreduplication.
The experimental unit is the cell, and therefore the percentage of cells with structural chromosomal aberration
(s) should be evaluated. Different types of structural chromosomal aberrations should be listed with their
numbers and frequencies for experimental and control cultures. Gaps are recorded separately and reported
but generally not included in the total aberration frequency. Various schemes involving varying degrees of
detail have been used to classify chromosomal aberrations. For most tests, it is adequate to classify
aberrations into four main categories; chromosome breaks, chromosome exchanges, chromatid breaks and
chromatid exchanges. In addition, other events such as polyploidy, endoreduplication, heavily damaged cells
(for example, more than ten aberrations in one cell), and cells with shattered or pulverized chromosomes
should also be recorded.
Concurrent measures of cytotoxicity for all treated and negative control cultures in the main aberration
experiment(s) should also be recorded.
Individual culture data should be provided. Additionally, all data should be summarised in tabular form.
C. Treatment
D. Harvest of Cultures
E. Chromosome Preparation
F. Analysis
VII. Data and Reporting
A. Treatment Results
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There is no requirement for verification of a clear positive response. Marginally or weakly positive results
should be verified by additional testing. Equivocal results should be clarified by further testing, preferably
using modification of experimental conditions. The need to confirm negative results has been discussed in
section V.D. "Harvest of Cultures". Modification of study parameters to extend the range of conditions
assessed should be considered in follow-up experiments. Study parameters that might be modified include the
concentration spacing and the metabolic activation conditions.
There are several criteria for determining a positive result, such as a concentration-related increase or a
reproducible increase in the number of cells with chromosomal aberrations at a single test concentration.
Statistical methods should be used as an aid in evaluating the test results 3, 13 but should not be the only
determining factor for a positive response. Biological relevance should be considered.
An increase in the number of polyploid cells may indicate that the test substance has the potential to interfere
with the mitotic processes and to induce numerical chromosomal aberrations. An increase in the number of
cells with endoreduplicated chromosomes may indicate that the test substance has the potential to inhibit cell
cycle progression 17, 18 . Induction of numerical aberrations should be confirmed.
Although most experiments will give clearly positive or negative results, in rare cases the data set will
preclude making a definite judgement about the activity of the test substance. Results may remain equivocal
or questionable regardless of the number of times the experiment is repeated.
Positive results from the in vitro chromosomal aberration test indicate that the test substance induces
structural chromosomal aberrations in cultured mammalian somatic cells. Negative results indicate that, under
the test conditions, the test substance does not induce chromosomal aberrations in cultured mammalian
somatic cells.
There are several conditions under which positive data may be a result of the test conditions rather than any
intrinsic clastogenicity of the test material. Changes in pH or osmolality have been shown to induce
aberrations 5, 19 . There is also evidence that some chemicals induce an increase in structural aberrations only
at high levels of cytotoxicity 20, 21
. In this case, the aberrations may be the result of disruption of cellular
processes that would not be expected at lower doses, and may therefore have no relevance to clastogenic risk
at physiologically relevant concentrations. However, before it can be concluded that the test agent presents no
clastogenic hazard, it must be demonstrated that the material is not genotoxic in any other in vitro assays, it
does not interact directly with the DNA, it is not a topoisomerase inhibitor, it is not related structurally to
known clastogens, and that the concentrations inducing aberrations in vitro cannot be achieved in vivo.
Caution should also be exercised when interpreting data from studies using Chinese hamster cells. Certain
chemicals appear to induce a high frequency of damage at a specific location, or fragile site, on the long arm
of the X chromosome 22, 23, 24 . In tests where it can be documented that a large percentage of aberrations
are at this site and there is no significant increase in other aberrations, the relevance of this phenomenon to
effects in human cells is unclear.
The test report should include the following information:
z identification data and CAS no., if known;
z physical nature and purity;
z physicochemical properties relevant to the conduct of the study;
z stability of the test substance, if known.
z justification for choice of solvent/vehicle.
z solubility and stability of the test substance in solvent/vehicle, if known.
z Time interval between stock solution and dosing solution preparation and use, and storage conditions.
z Data that verify concentration of the dosing solution, if available.
B. Evaluation and Interpretation of Results
C. Test Report
1. Test Substance
2. Solvent/Vehicle
3. Dosing Solutions
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z type and source of cells;
z karyotype features and suitability of the cell type used;
z absence of mycoplasma, if applicable;
z information on cell cycle length;
z sex of blood donors, whole blood or separated lymphocytes, mitogen used;
z number of passages, if applicable;
z methods for maintenance of cell cultures if applicable;
z modal number of chromosomes.
z identity of metaphase arresting substance, its concentration and duration of cell exposure;
z rationale for selection of concentrations and number of cultures including, e.g., cytotoxicity data and
solubility limitations, if available;
z composition of media, CO2 concentration if applicable;
z concentration of test substance;
z volume of vehicle and test substance added;
z incubation temperature;
z incubation time;
z duration of treatment;
z cell density at seeding, if appropriate;
z type and composition of metabolic activation system, including acceptability criteria;
z positive and negative controls;
z methods of slide preparation;
z criteria for scoring aberrations;
z number of metaphases analyzed;
z methods for the measurements of toxicity;
z criteria for considering studies as positive, negative or equivocal.
z signs of toxicity, e.g., degree of confluency, cell cycle data, cell counts, mitotic index;
z signs of precipitation;
z data on pH and osmolality of the treatment medium, if determined;
z definition for aberrations, including gaps;
z number of cells with chromosomal aberrations and type of chromosomal aberrations given separately for
each treated and control culture;
z changes in ploidy if seen;
z dose-response relationship, where possible;
z statistical analyses, if any;
z concurrent negative (solvent/vehicle) and positive control data;
z historical negative (solvent/vehicle) and positive control data, with ranges, means and standard
deviations.
4. Test cultures
5. Test Conditions
6. Results
7. Discussion of the Results
8. Conclusion
VIII. References
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1. 	Evans, H.J. (1976). Cytological Methods for Detecting Chemical Mutagens. In: Chemical Mutagens,
Principles and Methods for their Detection, Vol. 4, Hollaender, A. (ed) Plenum Press, New York and
London, pp. 1-29.
2. 	Ishidate, M. Jr. and Sofuni, T. (1985). The In Vitro Chromosomal Aberration Test Using Chinese
Hamster Lung (CHL) Fibroblast Cells in Culture. In: Progress in Mutation Research, Vol. 5, Ashby, J. et
al., (Eds) Elsevier Science Publishers, Amsterdam-New York- Oxford, pp. 427-432.
3. 	Galloway, S.M., Armstrong, M.J., Reuben, C., Colman, S., Brown, B., Cannon, C., Bloom, A.D.,
Nakamura, F., Ahmed, M., Duk, S., Rimpo, J., Margolin, G. H., Resnick, M. A., Anderson, G. and Zeiger,
E. (1987). Chromosome aberration and sister chromatid exchanges in Chinese hamster ovary cells:
Evaluation of 108 chemicals. Environ. Mol. Mutagen 10 (suppl. 10), 1-175.
4. 	Scott, D., Galloway, S.M., Marshall, R.R., Ishidate, Jr., M., Brusick, D., Ashby, J. and Myhr, B.C.,
(1991). Genotoxicity under Extreme Culture Conditions. A report from ICPEMC Task Group 9. Mutation
Res., 257, 147-204.
5. 	Morita, T., Nagaki, T., Fukuda, I. and Okumura, K., (1992). Clastogenicity of Low pH to Various
Cultured Mammalian Cells. Mutation Res., 268, 297-305.
6. 	Ames, B.N., McCann, J. and Yamasaki, E. (1975). Methods for Detecting Carcinogens and Mutagens
with the Salmonella/Mammalian Microsome Mutagenicity Test. Mutation Res., 31, 347-364.
7. 	Maron, D.M. and Ames, B.N. (1983). Revised Methods for the Salmonella Mutagenicity Test. Mutation
Res., 113, 173-215.
8. 	Natarajan, A.T., Tates, A.D, van Buul, P.P.W., Meijers, M. and de Vogel, N. (1976). Cytogenetic Effects
of Mutagens/Carcinogens after Activation in a Microsomal System In Vitro, I. Induction of Chromosome
Aberrations and Sister Chromatid Exchanges by Diethylnitrosamine (DEN) and Dimethylnitrosamine
(DMN) in CHO Cells in the Presence of Rat-Liver Microsomes. Mutation. Res., 37, 83-90.
9. 	Matsuoka, A., Hayashi, M. and Ishidate, M., Jr. (1979). Chromosomal Aberration Tests on 29 Chemicals
Combined with S9 Mix In vitro. Mutation. Res., 66, 277-290.
10. 	Elliot, B.M., Combes, R.D., Elcombe, C.R., Gatehouse, D.G., Gibson, G.G., Mackay, J.M. and Wolf, R.C.
(1992). Report of UK Environmental Mutagen Society Working Party. Alternatives to Aroclor 1254-
induced S9 in In Vitro Genotoxicity Assays. Mutagenesis, 7, 175-177.
11. 	Matsushima, T., Sawamura, M., Hara, K. and Sugimura, T. (1976). A Safe Substitute for Polychlorinated
Biphenyls as an Inducer of Metabolic Activation Systems. In: In Vitro Metabolic Activation in Mutagenesis
Testing, de Serres, F.J., Fouts, J.R., Bend, J.R. and Philpot, R.M. (eds), Elsevier, North-Holland, pp. 85-
88.
12. 	Galloway, S.M., Aardema, M.J., Ishidate, Jr., M., Ivett, J.L., Kirkland, D.J., Morita, T., Mosesso, P.,
Sofuni, T. (1994). Report from Working Group on In Vitro Tests for Chromosomal Aberrations. Mutation
Res., 312, 241-261.
13. 	Richardson, C., Williams, D.A., Allen, J.A., Amphlett, G., Chanter, D.O., and Phillips, B. (1989). Analysis
of Data from In Vitro Cytogenetic Assays. In: Statistical Evaluation of Mutagenicity Test Data. Kirkland,
D.J., (ed) Cambridge University Press, Cambridge, pp. 141-154.
14. 	Soper, K.A. and Galloway S.M. (1994). Replicate Flasks are not Necessary for In Vitro Chromosome
Aberration Assays in CHO Cells. Mutation Res., 312, 139-149.
15. 	Krahn, D.F., Barsky, F.C. and McCooey, K.T. (1982). CHO/HGPRT Mutation Assay: Evaluation of Gases
and Volatile Liquids. In: Genotoxic Effects of Airborne Agents, Tice, R.R., Costa, D.L., Schaich, K.M.
(eds.), New York, Plenum, pp. 91-103.
16. 	Zamora, P.O., Benson, J.M., Li, A.P. and Brooks, A.L. (1983). Evaluation of an Exposure System Using
Cells Grown on Collagen Gels for Detecting Highly Volatile Mutagens in the CHO/HGPRT Mutation Assay.
Environmental Mutagenesis, 5, 795-801.
17. 	Locke-Huhle, C. (1983) Endoreduplication in Chinese hamster cells during alpha-radiation induced G2
arrest. Mutation Res. 119, 403-413.
18. 	Huang, Y., Change, C. and Trosko, J.E. (1983) Aphidicolin - induced endoreduplication in Chinese
hamster cells. Cancer Res., 43, 1362-1364.
19. 	Galloway, S.M., Deasy, D.A., Bean, C.L., Kraynak, A.R., Armstrong, M.J., and Bradley, M.O. (1987)
Effects of high osmotic strength on chromosome aberrations, sister chromatid exchanges and DNA
strand breaks, and the relation to toxicity. Mutation Res., 189, 15-25.
20. 	Hilliard, C.A., Armstrong, M.J., Bradt, C.I., Hill, R.B., Greenwood, S.K. and Galloway, S.M. (1998)
Chromosome aberrations in vitro related to cytotoxicity of nonmutagenic chemicals and metabolic
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.oecd.org/
3. 	http://www.epa.gov/
poisons. Environ. Mol. Mutagen., 31, 316-326.
21. 	Galloway, S.M. (2000) Cytotoxicity and chromosome aberrations in vitro: experience in industry and the
case for an upper limit on toxicity in the aberration assay. Environ. Mol. Mutagen., 35: 191-201.
22. 	Yu, R.L., Aaron, C.S., Ulrich, R.G., Thilagar. A., Kumaroo, P.V. and Wang, Y. (1992) Chromosomal
breakage following treatment of CHO-K1 cells in vitro with U-68,553B is due to induction of
undercondensation of heterochormatin. Environ. Mol. Mutagen., 20, 172-187.
23. 	Blakey, D.H., K.L. Maus, R. Bell, J. Bayley, G.R. Douglas, and E.R. Nestmann, (1994). Mutagenic activity
of three industrial chemicals in a battery of in vitro and in vivo tests. Mutation Res., 320, 273-283.
24. 	Slijepcevic, P. and Natarajan, A.T. (1995) Fragile site at Xq21 in Chinese hamster and its implications
for the in vitro chromosomal aberration test. Mutagenesis, 10, 353-355.
25. 	Aardema, M.J., Albertini, S., Arni, P., Henderson, L.M., Kirsch-Volders, M., Mackay, J.M., Sarrif, A.M.,
Stringer, D.A., and Taalman, R.D.F., (1998). Aneuploidy: A report of an ECETOC task force. Mutation
Res., 410, 3-79.
26. 	Waters, M.D., Garrett, N.E., Covone-de-Serres, C.M., Howard, B.E., and Stack, H.F., 1983, Genetic
toxicology of some known or suspected human carcinogens. In: Chemical Mutagens: Principles and
Methods for Their Detection, de Serres, F.J. (ed.), Volume 8. New York, Plenum, chapter 9, pp. 261-341.
27. 	Brusick, D.J. 1987, Principles of Genetic Toxicology, 2nd Edition. Plenum, New York.
Links on this page:
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October 2001; Updated April 2006
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
An in vitro mammalian cell gene mutation test can be used to detect gene alterations induced by chemical
substances. While there are a number of cell lines that can be used, the L5178Y TK +/- -3.7.2C mouse
lymphoma cell line using the thymidine kinase (TK) gene is the cell line and assay of choice. The mouse
lymphoma assay (MLA) was chosen because of a body of research indicating that many types of genetic
alterations are detected. The assay detects mutations known to be important in the etiology of cancer and
other human genetically mediated illnesses. There is evidence that the assay detects gene mutations (point
mutations) and chromosomal events (deletions, translocations, mitotic recombination/gene conversion and
aneuploidy) (Applegate et. al., 1990; Hozier, et al., 1981; Moore, et al., 1985; Sawyer, et al., 1989; Sawyer,
et al., 1985). The efficiency of detection of all of these mutational events is still under investigation.
Other in vitro mammalian gene mutation assays exist including those that use either Chinese hamster cell
lines (CHO, AS52, and V79) or human lymphoblastoid cells (TK6). In these cell lines the most commonly used
genetic endpoints measure mutation at either the hypoxanthine-guanine phosphoribosyl transferase (HPRT), a
transgene of xanthine-guanine phosphoribosyl transferase (XPRT), or TK. The TK, HPRT and XPRT mutation
tests detect different spectra of genetic events. The autosomal location of TK allows for the detection of
genetic events that are not detected at the HPRT locus on the X-chromosome (Moore et al., 1989).
The various mutation assays are capable of detecting different spectra of genetic damage. Thus, it is not
expected that a chemical will give uniformly positive or negative results in the various assays. In particular,
the bacterial Salmonella assay detects only point and other very small-scale gene mutations. Furthermore, the
in vitro mammalian assays using the HPRT locus are unable to detect chemicals that do not induce point
mutations yet are clastogenic (Moore et. al, 1989). These chemicals are likely operating by mechanisms that
cause chromosomal mutations (deletions, translocations, gene conversion/mitotic recombination and/or
aneuploidy).
Additional information is provided in Chapter IV. C. 1. 2
Forward mutation: A mutation that converts a wild-type allele to a mutant allele.
Base-pair-substitution mutagens: Substances that cause substitution of one or a small number of base
pairs in the DNA.
Redbook 2000: IV.C.1.c Mouse Lymphoma Thymidine Kinase Gene Mutation Assay
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.1.c. Mouse Lymphoma Thymidine Kinase Gene Mutation Assay
I. Introduction
II. Definitions
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.1.c Mouse Lymphoma Thymidine Kinase Gene Mutation Assay
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Frameshift mutagens: Substances that cause insertion or deletion of a nucleotide pair or pairs, causing a
disruption of the triplet translational reading frame.
Phenotypic expression time: The time after treatment during which the genetic alteration is fixed within
the genome and any preexisting gene products are depleted to the point that the phenotypic trait is altered.
Mutant frequency: The number of mutant cells observed divided by the number of viable cells.
Relative survival (RS): The relative cloning efficiency of the test culture plated immediately after the cell
treatment and compared to the cloning efficiency of the negative control (Cole, et al., 1986)
Relative suspension growth (RSG): The relative total two day suspension growth of the test culture
compared to the total two-day suspension growth of the vehicle control. (Clive and Spector, 1975).
Relative total growth (RTG): RTG is used as the measure of treatment-related cytotoxicity in the MLA. It is
a measure of relative (to the vehicle control) growth of test cultures both during the two-day expression and
mutant selection cloning phases of the assay. The RSG of each test culture is multiplied by the relative cloning
efficiency of the test culture at the time of mutant selection and expressed relative to the cloning efficiency of
the vehicle control.
The established cell line L5178Y TK +/- -3.7.2C mouse lymphoma is used for the assay. The assay requires the
use of an exogenous source of metabolic activation. There are two versions of the assay, one using soft agar
cloning to enumerate mutants (Clive, et al., 1979 and Turner et al., 1984) and one using liquid media and
microwell plates (Cole, et al., 1986). Both versions of the assay are equally acceptable (Moore, et al., 2000).
Cells deficient in thymidine kinase (TK) due to the mutation TK+/- to TK -/- are resistant to the cytostatic
effects of the pyrimidine analogue trifluorothymidine (TFT). TK proficient cells are sensitive to TFT, which
causes the inhibition of cellular metabolism and halts further cell division. Thus, mutant cells are able to
proliferate in the presence of TFT, whereas normal cells, which contain the TK enzyme, are not.
Mouse lymphoma cells are grown and treated with test agents in suspension culture. Treatment should be
done both with and without exogenous metabolic activation. Following treatment, cells are cultured to allow
phenotypic expression prior to mutant selection. Cytotoxicity is measured and used to determine the
appropriate dose range of the test chemical. Mutant frequency is determined by seeding known numbers of
cells in medium containing the selective agent to detect the mutant cells, and in medium without the selective
agent to determine cloning efficiency (viability). After a suitable incubation time, the colonies are counted. The
mutant frequency is derived from the number of mutant colonies in the selective medium and the viability.
Because the assay was developed and characterized using the TK+/- -3.7.2C subline of L5178Y cells, it is
important that the assay be conducted using TK+/- -3.7.2C cells (Mitchell, et al., 1997). It is advisable for all
laboratories to karyotype the cells or paint the chromosome 11s to assure that there are two normal looking
chromosome 11s and to identify any other irregularities. The karyotype for the TK+/- -3.7.2.C cells has been
published (Sawyer, et al., 1985, 1989, 2006). The modal chromosome number for the L5178Y/TK+/- -3.7.2C
cell line is 40. There is one metacentric chromosome (t12;13) that should be counted as one chromosome.
Karyotyping and/or chromosome 11 painting should be performed when establishing a master stock. Cell
cultures need to be monitored for doubling times. Normal doubling times are generally between 8 and 10 hr.
Population doubling time should be checked when setting down master stocks. Cell cultures should always be
maintained under conditions that ensure that they are growing in log phase. As a general guidance, if a
laboratory is continually growing cells, the culture should be maintained for no longer than 3 months.
Appropriate culture media and incubation conditions (culture vessels, temperature, CO 2 concentration and
humidity) should be used. It is particularly important that culture conditions be chosen that ensure optimal
III. Initial Considerations
IV. Principle of the Test Method
V. Description of the Method
A. Preparations
1. Cells
2. Media and Culture Conditions
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growth of cells during the expression period and colony forming ability of both mutant and non-mutant cells.
For the MLA it is also important that the culture conditions ensure optimal growth of the small colony TK
mutants. Both Fischer's Medium for Leukemic Cells of Mice and RPMI 1640 media have been successfully used
with the MLA.
The osmolalilty and pH of the medium should be confirmed to be in the physiological range (300 ± 20 mOsm
and pH 7.0 ± 0.4). Each lot of horse serum should be tested for its ability to support optimal cell growth in
suspension culture (low and high cell densities), high plating efficiency and small colony mutant recovery
(Turner et al, 1984).
Cells are propagated from stock cultures, seeded in culture medium and incubated at 37o C. Prior to use, the
culture needs to be cleansed of pre-existing mutant cells. This is accomplished using methotrexate to select
against TK-deficient cells. Thymidine, hypoxanthine and guanine are added to the culture to ensure optimal
growth of the TK-competent cells (Turner et al., 1984).
Cells should be exposed to the test substance both in the presence and absence of an appropriate metabolic
activation system. The most commonly used system is a co-factor-supplemented post-mitochondrial fraction
(S9) prepared from the livers of rodents treated with enzyme-inducing agents such as Aroclor 1254 or a
combination of phenobarbitone and β-naphthoflavone (Mitchell, et al., 1997). The post-mitochondrial fraction
is usually used at concentrations in the range from 1-10% v/v in the final test medium. The choice and
condition of a metabolic activation system may depend upon the class of chemical being tested. In some cases
it may be appropriate to utilize more than one concentration of post-mitochondrial fraction. The use of
alternative metabolic activation systems such as primary hepatocytes (Brock, et al., 1987 and Oglesby, et al.,
1989) should be justified.
Liquid test substances may be added directly to the test system or diluted prior to treatment. Solid test
substances should be dissolved or suspended in appropriate solvents or vehicles and diluted if appropriate
prior to treatment of the cells. It should be noted that problems may occur, particularly with suspension
cultures, if the test substance precipitates either prior to addition to the cultures or during the treatment. It is
generally best to avoid testing chemicals using conditions where they are either insoluble or become insoluble
during the treatment. In some cases, it may be possible to use lower chemical concentrations and to increase
the treatment time (without metabolic activation) so that the test can be performed under conditions where
the chemical is soluble. Fresh chemical preparations should be employed unless stability data demonstrate the
acceptability of storage.
The properties of the test substance should be considered carefully if a base analogue or a compound related
to the selective agent is tested in the MLA. For example, any suspected selective toxicity by the test substance
for mutant and non-mutant cells should be investigated. If mutants and non-mutant cells are differentially
sensitive to the test agent, the preexisting spontaneous mutants may be selectively increased in frequency
during the treatment. The resultant increase in mutant frequency would be due to that selection of pre-
existing spontaneous mutants rather than from the induction of new mutations. This possibility needs to be
considered and investigated when the test chemical is structurally related to TFT.
The solvent/vehicle should be chosen to maximize the solubility of the test agent. However, it should not be
suspected of chemical reaction with the test substance and should be compatible with the survival of the cells
and the S9 activity. If other than well-known solvent/vehicles are used, their inclusion should be supported by
data indicating their compatibility. It is recommended that wherever possible, the use of an aqueous
solvent/vehicle be considered first. When testing water-unstable substances, the organic solvents used should
be free of water. Water can be removed using a molecular sieve. Organic solvents that have been used with
the MLA include DMSO, acetone and ethyl alcohol.
Criteria to be considered when determining the highest test concentration include cytotoxicity, solubility in the
test system, and changes in pH or osmolality. For relatively non-cytotoxic compounds the maximum
3. Preparation of Cultures
4. Metabolic Activation
5. Test Substance/Preparations
B. Test Conditions
1. Solvent/vehicle
2. Exposure Conditions
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concentration should be 5 mg/ml, 5 l/ml or 0.01 M, whichever is lowest.
Relatively insoluble substances should be tested up to or beyond their limit of solubility under the culture
conditions, although care should be exercised to minimize conditions that complicate quantification of results.
Evidence of insolubility should be determined in the final treatment medium to which cells are exposed. It may
be useful to assess solubility at the beginning and end or the treatment, as solubility can change during the
course of exposure in the test system due to the presence of cells, S9, serum etc. Insolubility may be
assessed using the naked eye.
In the MLA where the cells are grown in suspension, testing compounds in the precipitating range is
problematical with respect to defining the exposure period. After the defined exposure period, the cells are
normally pelleted by centrifugation and are then resuspended in fresh medium without the test compound. If
a precipitate is present, the compound will be carried through to the later stages of the assay making control
of exposure impossible. Therefore, for the MLA it is reasonable to use the lowest precipitating concentration as
the highest concentration tested or the highest test concentration used in the data evaluation. This should
help to minimize conditions that could complicate quantification of results.
Cytotoxicity should be determined for each individual test and control culture. For the soft agar version of the
MLA, this has generally been done using the relative total growth (RTG) which was originally defined by Clive
and Spector (1975). This measure includes the relative growth in suspension during the expression time and
the relative cloning efficiency at the time that mutants are selected. The microwell version of the assay was
developed using the relative survival (RS) as the cytotoxicity measure. The RS is determined by the relative
plating efficiency of each culture when plated immediately after the exposure period. The RTG and the RS are
different measures of cytotoxicity and, although there is no real justification that one measure is superior to
the other, it is important that the same measure of cytotoxicity be used for both versions of the assay.
Because the RS is not normally measured in the soft agar version of the assay and the RTG is measured in
both versions, it is recommended that the RTG be used as the standard measure of cytotoxicity. This
cytotoxicity value is used both to determine the required concentration range for an acceptable test and for
establishing the highest concentration that is used for defining positive and negative responses (Moore, et al.,
2000).
There are additional considerations in the calculation of the RTG between the two methods for the conduct of
the MLA. In the agar method, the cells are exposed to the test chemical, the chemical is removed by
centrifugation and resuspension in fresh medium. The first cell count takes place approximately 24 hrs after
the initiation of the chemical exposure. On the first day following treatment, the cell density for each culture is
readjusted, generally to 0.2 or 0.3 × 106 cells per ml of medium. Treated cultures with densities less than 0.2
or 0.3 × 106 cells per ml of medium are generally not adjusted in their density, and usually have sustained
too much cytotoxicity to carry through the full experiment for mutant enumeration. For each treatment
culture, the relative cell growth (compared to control) is calculated. On the second day following treatment,
the cultures are again counted, adjusted in density and prepared to clone for mutant enumeration. The total
two-day suspension growth of each culture is calculated and each treated culture is compared to the control.
This value is referred to as the relative suspension growth (RSG). Cultures are cloned with and without
selective medium to enumerate mutants and to calculate the mutant frequency (number of mutants per 106
cloneable cells). The relative plating efficiency for each culture is determined (relative to the negative control)
and multiplied by the RSG to obtain a relative total growth (RTG).
In the microwell method, most laboratories count the cell cultures immediately following exposure to the test
chemical and adjust the density of the cultures. Following the end of treatment and the adjustment of cell
density, the cell cultures are handled just like the cultures in the agar method. Following the two-day
expression period, the cultures are plated in 96-well plates, with and without TFT selection.
As described above, handling of the cell cultures following treatment differs significantly between the two
methods This difference impacts the calculation of the RSG and RTG. The RSG and the RTG, in the agar
method, are calculated to include any differences that may occur in cell growth between the chemically
treated and control cultures. However, in the microwell method, the cultures are generally adjusted in density
following treatment and the RS, RSG and RTG calculated using the plating efficiency and cell growth that
occurs following treatment. In other words, any differential growth that occurs between the negative controls
and the treatment cultures during the treatment phase of the assay is not factored into the calculation.
To make the cytotoxicity measures obtained in the two versions equivalent, it is necessary for users of the
microwell method to adjust their RS, RSG and RTG values to include the differential growth that can occur
during treatment. This adjustment should be made by comparing the cell density in each treated culture with
3. Cytotoxicity
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that of the negative control immediately following treatment. By comparing the growth of each treated culture
relative to the control, it is possible to calculate a relative growth during treatment factor that can then be
used to adjust the RS, RSG and RTG. As an example, if following the treatment period, the negative control
had a cell density of 0.6 × 10 6 cell/ml and the treated culture had a density of 0.3 × 106 cell/ml, then the
relative growth during treatment for that treated culture is 0.5 (or 50%). If the RS for that culture is
determined to be 0.4 then the adjusted RS would be calculated as the RS × the relative growth during
treatment or 0.4 × 0.5=0.20 (or 20%). The RSG would be adjusted in the same manner. The adjusted RTG
would be obtained by multiplying the adjusted RSG by the relative plating efficiency at the time of mutant
selection.
The selection and spacing of doses is a critical factor in the proper conduct of the MLA. It is desirable to have
more than one data point that can be used to confirm a positive or negative response. The assay may be
conducted using either single cultures per dose point or multiple cultures per dose point. The strategy for
determining the number of doses and the selection and spacing of doses can vary based on the toxicity range
of the test material being evaluated and degree by which the chemical does or does not increase mutant
frequency. It is not necessary to have a prescribed number of analyzable cultures when the chemical is clearly
positive. When the chemical is not mutagenic or is only weakly mutagenic, generally, at least 4 analyzable
doses are required when duplicate cultures are used and 8 analyzable doses are required when single cultures
are used.
For toxic test materials, the highest dose level should induce an 80% reduction in RTG. Dose levels that
induce more than a 90% reduction in RTG are usually excluded from the evaluation. However, as noted below,
there are circumstances where the data points obtained at less than 10% RTG can be useful in the final
evaluation.
While it is generally advisable to obtain data points covering the entire 100 to 10% RTG range, the validity of
a test does not always depend upon attaining such a complete dose-response. When a test material induces
large increases in mutant frequency, it is generally sufficient to provide data points anywhere within the 100-
10% RTG range. For test materials that are not mutagenic or that induce only weak mutagenic responses, it is
advisable to place emphasis on selecting doses that are expected to produce higher toxicity. This increases the
probability of obtaining data points that can be used to make a definitive evaluation, that is, data points in the
approximately 10-20% RTG range.
Therefore, it is recommended that laboratories attempt to achieve a maximum dose with RTG values between
10-20%. However, as already indicated, if a chemical clearly satisfies the criteria for a positive response the
result will still be valid even if there is no test concentration resulting in 10-20% RTG.
When the mutant frequency is elevated at one or more doses above the background frequency (yet has not
reached a level to be determined positive), interpretation of the test, and therefore its validity, will depend
upon at least one dose that results in an RTG within the 10-20% range. This may only be achievable by
conducting a repeat experiment in which the dose range is modified to increase the probability of attaining
data points within the 10-20% RTG range.
There are some circumstances under which a chemical may be determined to be nonmutagenic when there is
no culture showing an RTG value between 10-20 % RTG. These situations are outlined as follows: (1) There is
no evidence of mutagenicity (e.g., no dose response, no mutant frequencies above those seen in the
concurrent negative control or historical background ranges, etc.) in a series of data points within 100% to
20% RTG and there is at least one data point between 20 and 25% RTG. (2) There is no evidence of
mutagenicity (e.g., no dose response, no mutant frequencies above those seen in the concurrent negative
control or historical background ranges, etc.) in a series of data points between 100% to 25% and there is
also a negative data point between 10% and 1% RTG.
Significant increases in mutant frequencies seen only at RTG <10%, but with no evidence of mutagenicity at
RTG >10%, do not constitute a positive result.
Concurrent positive and negative (solvent or vehicle) controls both with and without metabolic activation
should be included in each experiment. When metabolic activation is used, the positive control chemical
should be one that requires activation to give a mutagenic response.
Positive controls should induce mostly small colony TK mutants. One appropriate positive control in the
absence of S9 metabolic activation is methyl methanesulfonate. Appropriate positive controls to be used with
S9 activation include cyclophosphamide (monohydrate), benzo(a)pyrene, and 3-methylcholanthrene. Positive
4. Dose Selection
5. Controls
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control responses with and without S9 should be used for quality control measures and to demonstrate
adequate detection of small colony mutants. Each laboratory must establish its own historical database for its
positive and negative controls.
Negative controls, consisting of solvent or vehicle alone in the treatment medium, and treated in the same
manner as the treatment groups should be included. In addition, untreated controls should also be used
unless there are historical data demonstrating that no deleterious or mutagenic effects are induced by the
chosen solvent.
Cells, growing in log phase, should be exposed to the test substance both with and without metabolic
activation. Exposure should be for a suitable period of time (generally 3-4 hrs is used). However, it may also
be advisable (particularly for chemicals demonstrating insolubility) to extend the treatment time (without
metabolic activation) to 24 hrs. The International Conference on Harmonisation 3
has recommended that all
chemicals that are negative following the standard 3-4 hr treatment be evaluated (without metabolic
activation) using a 24-hr treatment.
Either duplicate or single treated cultures may be used at each concentration tested. In either event, the
number of concentrations used must be sufficient to provide confidence in the evaluation. Particularly, in
situations where the chemical is negative or weakly positive, it may be advisable to use single treated
cultures, and increase the number of different concentrations evaluated in a single experiment. Because of the
importance of the negative controls, it is recommended that duplicate negative (solvent) control cultures be
used.
Gaseous or volatile substances should be tested by appropriate methods, such as in sealed culture vessels.
At the end of the exposure period, cells are washed and cultured to allow for the expression of the mutant
phenotype.
Each locus has a defined minimum time requirement to allow near optimal phenotypic expression of newly
induced mutants. For the TK locus that time is 2 days (Moore and Clive, 1982). Following the expression
period, cells are grown in medium with and without selective agent for the determination of the numbers of
mutants and cloning efficiency (used to calculate mutant frequency), respectively. This mutant selection can
be accomplished using TFT selection (Moore-Brown et al., 1981) and either the soft agar or the microwell
cloning method (Moore et al., 2000).
In the soft agar method, the mutant frequency (MF) is determined by counting the number of TFT resistant
colonies and correcting the number of cells plated for selection by the plating efficiency (PE). That is, the MF =
(number of mutants/number of cells plated) × PE. For the microwell method, the plating efficiency (PE) and
the mutant frequency (MF) are calculated using the Poisson distribution. The plating efficiency (PE) in both the
mutant selection plates and the viability plates is calculated as follows: From the zero term of the Poisson
distribution, the probable number of clones/well (P) is equal to -ln(EW/TW), where EW = empty wells and TW
= total wells. The PE = P/Number of cells plated per well. The mutant frequency is then calculated: MF = (PE
(mutant)/PE(viable)) × 10 6
.
If the test substance is positive in the MLA, mutant colony sizing should be performed on at least one of the
test cultures (generally the highest acceptable positive concentration) and on the negative and positive
controls. Colony sizing can be used to provide general information concerning the ability of the test chemical
to cause point mutations and/or chromosomal events. If the test substance is negative, mutant colony sizing
should be performed on the negative and positive controls. Colony sizing on the negative control is needed to
demonstrate that large colonies are growing adequately. The test chemical cannot be determined to be
negative if the positive control does not demonstrate the appropriate level of small mutant colony induction
and detection.
Data should include cytotoxicity and plating efficiency determination, colony counts and mutant frequencies
C. Procedure
1. Treatment with test substance
2. Expression time and measurement of mutant frequency
3. Mutant Colony Sizing
VI. Data and Reporting
A. Treatment of results
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for the treated and control cultures. In the case of a positive response, mutant colonies are scored using the
criteria of small and large colonies on at least one concentration of the test substance (highest positive
concentration) and on the negative and positive controls.
The molecular and cytogenetic nature of both large and small colony mutants has been explored in detail
(Applegate, et al, 1990, Hozier et al., 1981, 1985 and Moore et al., 1985). Small and large colony mutants are
distinguished by growth rate, and therefore they form colonies of differing size. Mutant cells that have
suffered the most extensive genetic damage have prolonged doubling times and thus form small colonies. The
induction of small colony mutants has been associated with chemicals that induce chromosomal aberrations.
Less seriously affected mutant cells grow at rates similar to the parental cells and form large colonies.
The RS (if determined), RTG and RSG should be given. Mutant frequency should be expressed as number of
mutant cells per number of surviving cells.
Individual culture data should be provided in tabular form that can be cross-referenced to the summary data.
Additionally, all data should be summarized in tabular form.
While there is no requirement for verification of a clear positive response, a confirmatory experiment is often
useful. Experiments that do not provide enough information to determine whether the chemical is positive or
negative should be clarified by further testing preferably by modifying the test concentrations. Negative
results using the short (3-4 hr) treatment should be confirmed by repeat testing using 24-hr treatment
without metabolic activation. Modification of study parameters to extend the range of conditions assessed
should be considered in follow-up experiments for either equivocal or negative results. Study parameters that
might be modified include the concentration spacing and the metabolic activation conditions.
There are several criteria for determining a positive result, such as a concentration-related, or a reproducible
increase in mutant frequency. The U.S. EPA MLA Gene-Tox Workgroup developed criteria for evaluating the
published literature. These criteria for positive and negative (and other responses) can be used as guidance in
interpreting data (Mitchell, et al., 1997). Statistical methods may be used as an aid in evaluating the test
results. Statistical significance should not be the only determining factor for a positive response. Biological
relevance of the results should also be considered. The MLA Workgroup of the International Workshop for
Genotoxicity Testing recommends acceptance criteria the MLA and the use of a global evaluation factor
combined with statistical analysis for the interpretation of MLA data (Moore et al., 2006).
Although most studies will give clearly positive or negative results, in rare cases the data set will preclude
making a definite judgement about the activity of the test substance. In these situations, a chemical will give
equivocal results in two or more very well conducted studies. In those situations, it is generally not useful to
conduct a further study. Such chemicals are not negative and they should be considered to be borderline
responses.
Positive results for the MLA indicate that the test substance induces mutations affecting the expression of the
thymidine kinase gene in the cultured mammalian cells used. A positive concentration-related response that is
reproducible is most meaningful. Negative results indicate that, under the test conditions, the test substance
does not induce mutations affecting the thymidine kinase gene in the mouse lymphoma cells.
It should be noted that positive results that may not be relevant to the in vivo situation may arise in vitro
from changes in pH, osmolality or high levels of cytotoxicity (Brusick, 1986, Mitchell, et al., 1997 and Scott, et
al., 1991).
The test report should include the following information:
z identification data and CAS no., if known;
z physical nature and purity;
z physicochemical properties relevant to the conduct of the study;
z stability of the test substance-including both the "neat" sample and the sample in the
solvent/vehicle/medium. This should be done both prior to and at the end of the treatment period.
B. Evaluation and interpretation of results
VII. Test Report
A. Test substance:
B. Solvent/Vehicle:
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z justification for choice of vehicle/solvent;
z solubility and stability of the test substance in solvent/vehicle, if known.
z type and source of cells
z karyotype of cells
z number of cell cultures;
z methods for maintenance of cell cultures;
z absence of mycoplasma.
z rationale for selection of concentrations and number of cell cultures including e.g., cytotoxicity
z data and solubility limitations, if available;
z composition of media, C02 concentration;
z concentration of test substance;
z volume of vehicle and test substance added;
z incubation temperature;
z incubation time;
z cell density during treatment;
z type and composition of metabolic activation system including acceptability criteria;
z positive and negative controls;
z length of expression period (including number of cells seeded, and subcultures and feeding schedules, if
appropriate);
z selective agent(s);
z criteria for considering tests as positive, negative or equivocal;
z methods used to enumerate numbers of viable and mutant cells.
z definition of colonies of which size and type are considered (including criteria for "small' and "large"
colonies, as appropriate).
z signs of toxicity;
z signs of precipitation;
z data on pH and osmolality during the exposure to the test substance, if determined;
z colony sizing (for positive test chemicals) and for the negative and positive control
z dose-response relationship, where possible;
z statistical analyses, if any;
z concurrent negative (solvent/vehicle) and positive control data;
z historical negative (solvent/vehicle) and positive control data with ranges, means and standard
deviations; number of tests upon which the historical controls are based;
z mutant frequency;
z Raw data, including cell culture counts and colony counts
The following references should be consulted for additional background information on this test guideline.
C. Cells:
D. Test conditions:
E. Results:
F. Discussion of the results:
G. Conclusion:
VIII. References
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1. 	Applegate, M.L., Moore, M.M., Broder, C.B., Burrell, A., and Hozier, J.C. (1990). Molecular Dissection of
Mutations at the Heterozygous Thymidine Kinase Locus in Mouse Lymphoma Cells. Proc. Natl.
Acad.Sci.USA, 87:51-55.
2. 	Brock, K.H., Moore, M.M, and Oglesby L.A. (1987) Development of an intact hepatocyte activation
system for routine use with the mouse lymphoma assay. Environ. Mutagen, 9:331-341.
3. 	Brusick, D., 1986. Genotoxic effects in cultured mammalian cells produced by low pH treatment
conditions and increased ion concentrations. Environ. Mutagen, 8: 879-886.
4. 	Clive, D. and Spector, J.F.S., 1975. Laboratory procedure for assessing specific locus mutations at the
TK locus in cultured L5178Y mouse lymphoma cells. Mutat. Res., 31: 17-29.
5. 	Clive, D., Johnson, K.O., Spector, J.F.S., Batson, A.G., and Brown M.M.M. (1979). Validation and
Characterization of the L5178Y/TK+/-- Mouse Lymphoma Mutagen Assay System. Mutat. Res., 59: 61-
108.
6. 	Cole, J., Muriel, W.J., and Bridges, B.A. (1986) The mutagenicity of sodium fluoride to L5178Y (wild-type
and TK+/- (3.7.2C)) mouse lymphoma cells. Mutagenesis, 1:157-167.
7. 	Hozier, J., Sawyer, J., Moore, M., Howard, B., and Clive D. (1981) Cytogenetic analysis of the
L5178Y/TK +/- --> TK -/- mouse lymphoma mutagenesis assay system, Mutat. Res.,, 84: 169-181.
8. 	Hozier, J., Sawyer, J., Clive, D., and Moore, M.M. (1985) Chromosome 11 aberrations in small colony
L5178Y TK -/- mutants early in their clonal history, Mutat. Res., 147: 237-242.
9. 	Mitchell, A.D., Auletta, A.E., Clive, D.C., Kirby, P.E., Moore, M.M., and Myhr, B.C. (1997) The
L5178Y/tk+/- mouse lymphoma specific gene and chromosomal mutation assay: A phase III report of
the US Environmental Protection Agency Gene-Tox Program, Mutat. Res., 394: 177-303.
10. 	Moore-Brown, M.M., Clive, D., Howard, B.E., Batson, A.G., and Johnson, K.O. (1981) The utilization of
trifluorothymidine (TFT) to select for thymidine kinase-deficient (TK -/- ) mutants from L5178Y/TK +/-
mouse lymphoma cells, Mutat. Res., 85: 363-378.
11. 	Moore, M.M. and Clive, D. (1982) The quantitation of TK-/- and HGPRT - mutants of L5178Y/TK +/- mouse
lymphoma cells at varying times post treatment, Environ. Mutagen., 4: 499-519.
12. 	Moore, M.M., Clive, D., Hozier, J.C., Howard, B.E., Batson, A.G., Turner, N.T., and Sawyer, J. (1985).
Analysis of Trifluorothymidine-Resistant (TFT) Mutants of L5178Y/TK- Mouse Lymphoma Cells. Mutation
Res., 151: 161-174.
13. 	Moore, M.M., Harrington-Brock, K., Doerr, C.L., and Dearfield, K.L. (1989). Differential Mutant
Quantitation at the Mouse Lymphoma TK and CHO HGPRT Loci. Mutagenesis, 4: 394-403.
14. 	Moore, M.M. (Chair), Honma, M. (Co-Chair), Clements, J. (Rapporteur), Awogi, T., Bolcsfoldi, G., Cole,
J., Gollapudi, B., Harrington-Brock, K., Mitchell, A., Muster, W., Myhr, B., O'Donovan, M., Ouldelhkim,
M.-C., San, R., Shimada, H., and Stankowski, L.F. Jr. (2000) The mouse lymphoma thymidine kinase
locus (tk) gene mutation assay: International Workshop on Genotoxicity Test Procedures (IWGTP)
Workgroup Report, Environ. Mol. Mutagen., 35: 185-190.
15. 	Moore, M.M., M. Honma, J. Clements, G. Bolcsfoldi, B. Burlinson, M. Cifone, J. Clarke, R. Delongchamp,
R. Durward, M. Fellows, B. Gollapudi, S. Hou, P. Jenkinson, M. Lloyd, J. Majeska, B. Myhr, M. O'Donovan,
T. Omori, C. Riach, R. San, L.F. Stankowski, Jr., A. Thakur, F. Van Goethem, S. Wakuri and I.
Yoshimura. (2006) Mouse Lymphoma Thymidine Kinase Gene Mutation Assay: Follow-up Meeting of the
International Workshop on Genotoxicity Tests-Aberdeen, Scotland, 2003-- Assay acceptance criteria,
positive controls, and data evaluation. Environ. Mol. Mutagen. 47:1-5.
16. 	Oglesby, L.A., Harrington-Brock, K., and Moore, M.M. (1989) Induced hepatocytes as a metabolic
activation system for the mouse-lymphoma assay, Mutat. Res., 223: 295-302.
17. 	Sawyer, J.R., Moore, M.M., and Hozier, J.C. (1989) High resolution cytogenetic characterization of the
L5178Y TK +/- mouse lymphoma cell line, Mutat. Res., 214: 181-193.
18. 	Sawyer, J., Moore, M.M., Clive, D., and Hozier, J. (1985) Cytogenetic characterization of the L5178Y
TK +/- 3.7.2C mouse lymphoma cell line, Mutat. Res., 147: 243-253.
19. 	Sawyer, J.R., R.L. Binz, J. Wang and M.M. Moore. (2006) Multicolor spectral karyotyping of the L5178Y
TK+/--3.7.2C mouse lymphoma cell line. Environ. Mol. Mutagen., 47:127-131.
20. 	Scott, D., Galloway, S.M., Marshall, R.R., Ishidate, M., Brusick, D., Ashby, J., and Myhr, B.C. (1991).
Genotoxicity Under Extreme Culture Conditions. A report from ICPEMC Task Group 9. Mutation Res.,
257: 147-204.
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078321.htm
3. 	http://www.ich.org
21. 	Turner, N.T., Batson, A.G., and Clive, D. (1984). Procedures for the L5178Y/TK+/- - TK-/- Mouse
Lymphoma Cell Mutagenicity Assay. In: Kilbey, B.J. et al. (eds.) Handbook of Mutagenicity Test
Procedures, Elsevier Science Publishers, New York, pp. 239-268.
Links on this page:
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July 2000
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
Micronuclei are cytoplasmic chromatin-containing bodies formed when acentric chromosome fragments or
chromosomes lag during anaphase and fail to become incorporated into daughter cell nuclei during cell
division. Because genetic damage that results in chromosome breaks, structurally abnormal chromosomes, or
spindle abnormalities leads to micronucleus formation, the incidence of micronuclei serves as an index of
these types of damage. It has been established that essentially all agents that cause double strand
chromosome breaks (clastogens) induce micronuclei. Because enumeration of micronuclei is much faster and
less technically demanding than is scoring of chromosomal aberrations, and because micronuclei arise from
two important types of genetic damage (clastogenesis and spindle disruption), the micronucleus assay has
been widely used to screen for chemicals that cause these types of damage.
This guidance addresses the most widely used in vivo micronucleus assay: the mammalian erythrocyte
micronucleus assay. This in vivo micronucleus test is used for the detection of damage induced by the test
substance to the chromosomes or the mitotic apparatus of erythroblasts by analysis of erythrocytes as
sampled in bone marrow and/or peripheral blood cells of animals, usually rodents.
The purpose of the micronucleus test is to identify substances that cause cytogenetic damage which results in
the formation of micronuclei containing lagging chromosome fragments or whole chromosomes.
When a bone marrow erythroblast develops into a polychromatic erythrocyte, the main nucleus is extruded;
micronuclei that have been formed may remain behind in the otherwise enucleated cytoplasm. Visualization of
micronuclei is facilitated in these cells using specific staining techniques and because they lack a main
nucleus. An increase in the frequency of micronucleated polychromatic erythrocytes in treated animals is an
indication of induced chromosome damage.
Centromere (Kinetochore) is a region(s) of a chromosome with which spindle fibers are associated during
cell division, allowing orderly movement of daughter chromosomes to the poles of the daughter cells.
Micronuclei are small nuclei, separate from and additional to the main nuclei of cells, produced during
telophase of mitosis (meiosis) by lagging chromosome fragments or whole chromosomes.
Normochromatic erythrocyte is a mature erythrocyte that lacks ribosomes and can be distinguished from
Redbook 2000: IV.C.1.d Mammalian Erythrocyte Micronucleus Test
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.1.d. Mammalian Erythrocyte Micronucleus Test
I. Introduction
II. Definitions
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
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immature, polychromatic erythrocytes by stains selective for ribosomes.
Polychromatic erythrocyte is an immature erythrocyte, in an intermediate stage of development, that still
contains ribosomes and therefore can be distinguished from mature, normochromatic erythrocytes by stains
selective for ribosomes.
The bone marrow of rodents is routinely used in this test since polychromatic erythrocytes are produced in
that tissue. The measurement of micronucleated immature (polychromatic) erythrocytes in peripheral blood is
equally acceptable in any species in which the inability of the spleen to remove micronucleated erythrocytes
has been demonstrated, or which has shown an adequate sensitivity to detect agents that cause structural
and/or numerical chromosome aberrations. Micronuclei can be distinguished by a number of criteria. These
include identification of the presence or absence of a kinetochore or centromeric DNA in the micronuclei. The
frequency of micronucleated immature (polychromatic) erythrocytes is the principal endpoint. The number of
mature (normochromatic) erythrocytes in the peripheral blood that contain micronuclei among a given number
of mature erythrocytes can also be used as the endpoint of the assay when animals are treated continuously
for a period that exceeds the lifespan of the erythrocyte in the species under consideration (e.g., 4 weeks in
the mouse), provided that significant splenic selection against micronucleated erythrocytes does not occur in
that species/strain. The consequences of splenic selection, if it occurs, should be fully addressed.
This mammalian in vivo micronucleus test is especially relevant to assessing mutagenic hazard in that it allows
consideration of factors of in vivo metabolism, pharmacokinetics and DNA-repair processes although these
may vary among species, among tissues and among genetic endpoints. An in vivo assay is also useful for
further investigation of a mutagenic effect detected by an in vitro system.
If there is evidence that the test substance, or a reactive metabolite, will not reach the target tissue, it is not
appropriate to use this test.
Animals are exposed to the test substance by an appropriate route. If bone marrow is used, the animals are
sacrificed at appropriate times after treatment, the bone marrow extracted, and preparations made and
stained.(16),(17),(18),(26),(32),(41) When peripheral blood is used, the blood is collected at appropriate times
after treatment and smear preparations are made and stained.(4),(5),(14),(16),(27),(28),(29),(32) Preparations are
analyzed for the presence of micronuclei.
Historically, mice or rats have been used routinely for this assay. If bone marrow is the tissue sampled, any
appropriate mammalian species may be used (see section III. 2 , above). As with any toxicology study,
selection of the appropriate species should be justified. When peripheral blood is used, mice are
recommended. However, any appropriate mammalian species may be used provided it is a species in which
the spleen does not remove micronucleated erythrocytes or is a species which has shown an adequate
sensitivity to detect agents that cause structural and/or numerical chromosome aberrations. Commonly used
laboratory strains of young healthy animals should be employed. At the commencement of the study, the
weight variation of animals should be minimal and not exceed ±20% of the mean weight of each sex.
The temperature in the experimental animal room should be appropriate for the species used; for mice and
rats this should be 22°C (±3°C). Although the relative humidity should be at least 30% and preferably not
exceed 70% other than during room cleaning, the aim should be 50-60%. Lighting should be artificial, the
sequence being 12 hours light, 12 hours dark. For feeding, conventional laboratory diets may be used with an
unlimited supply of drinking water. The choice of diet may be influenced by the need to ensure a suitable
admixture of a test substance when administered by this route. Animals may be housed individually, or caged
in small groups of the same sex.
III. Initial Considerations
IV. Principle of the Test Method
V. Description of the Method
A. Preparations
1. Selection of Animal Species
2. Housing and Feeding Conditions
3. Preparation of the Animals
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Healthy young adult animals should be randomly assigned to the control and treatment groups. The animals
should be identified uniquely. The animals should be acclimated to the laboratory conditions for at least five
days. Cages should be arranged in such a way that possible effects due to cage placement are minimized.
Solid test substances should be dissolved or suspended in appropriate solvents or vehicles and diluted, if
appropriate, prior to dosing of the animals. Liquid test substances may be dosed directly or diluted prior to
dosing. Fresh preparations of the test substance should be employed unless stability data demonstrate the
acceptability of storage.
The solvent/vehicle should not produce toxic effects at the dose levels used, and should not be suspected of
chemical reaction with the test substance. If other than commonly employed solvents/vehicles are used, their
use should be supported with reference data indicating their compatibility with the test 3 substance and the
animals. It is recommended that, wherever appropriate, the use of an aqueous solvent/vehicle should be
considered first.
Concurrent positive and negative (solvent/vehicle) controls should generally be included for each sex in each
test conducted with rodents. However, when the micronucleus assay is conducted as part of a general toxicity
study according to GLP guidelines, then verification of appropriate dosing will be performed by chemical
analysis. In such cases, concurrent treatment of animals with a positive control agent may not be necessary
and control of staining and scoring procedures may be accomplished by including appropriate reference
samples obtained previously from animals that are not part of the current experiment. In studies with higher
species, such as primates or dogs, positive controls may be omitted provided that an acceptable response to
positive control substances of the species used has been demonstrated previously by the testing laboratory. In
all cases, concurrent negative controls are an obligatory study component. Except for treatment with the test
substance, animals in the control groups should be handled in an identical manner to animals of the treatment
groups.
Positive controls should produce micronuclei in vivo at exposure levels expected to give a detectable,
statistically significant increase over background. Positive control doses should be chosen so that the effects
are clear but do not immediately reveal the identity of the coded slides to the reader. It is acceptable that the
positive control be administered by a route different from the test substance and sampled at only a single
time. In addition, the use of chemical class-related positive control chemicals may be considered, when
available. Examples of positive control substances include:
Negative control animals, treated with solvent or vehicle alone and otherwise treated in the same way as the
treatment groups, should be included for every sampling time, except that under appropriate circumstances it
may be possible to use an animal as its own control by comparing pre-treatment and post-treatment samples.
If single sampling is applied for negative controls, the sampling time chosen should be justified. In addition,
untreated controls should also be used unless there are (a) data available from the test laboratory, or (b)
historical or published control data demonstrating that no deleterious or mutagenic effects are induced by the
chosen solvent/vehicle.
If peripheral blood is used, a pre-treatment sample may also be acceptable as a concurrent negative control,
but only in the short peripheral blood studies (e.g., 1-3 treatment(s)) when the resulting data are in the
expected range for the historical control and when the absence of a solvent effect has been demonstrated.
The following sections provide guidance for procedures in mice and rats, the species used most commonly in
4. Preparation of Doses
B. Test Conditions
1. Solvent/Vehicle
2. Controls
Chemical 	CAS Number
Ethyl methanesulphonate 	62-50-0
Ethyl nitrosourea 	759-73-9
Mitomycin C 	50-07-7
Cyclophosphamide
(monohydrate) 50-18-0 (6055-19-2)
Triethylenemelamine 	51-18-3
VI. Procedure for Rats and Mice
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this assay.
Each treated and control group should include at least 5 analyzable animals per sex.(12) If at the time of the
study there are data available from studies in the same species and using the same route of exposure that
demonstrate that there are no substantial differences between sexes in toxicity, then testing in a single sex
will be sufficient.
Several different treatment schedules (i.e., 1, 2, or more treatments at 24 hr intervals) can be recommended.
Samples from extended dose regimens are acceptable as long as a positive effect has been demonstrated for
this study or, for a negative study, as long as toxicity has been demonstrated or the limit dose (see section
"D", below) has been used, and dosing continued until the time of sampling. This is based on studies showing
that repeated exposures of mice and rats of up to subchronic duration produced effects of a magnitude similar
to those obtained with the traditional acute assay.(1),(2),(8),(11),(19),(21),(22),(23),(25),(29),(37),(38),(44),(48),(50)
However, because there is some concern that sensitivity might be reduced in longer term studies due to a
failure to achieve a true MTD, or because adaptation may occur, it is currently considered that the duration
treatment should be limited to four weeks until the sensitivity of the assay is confirmed when longer
treatments are used.(12)
Test substances may also be administered as a split dose, i.e., two or more treatments on the same day
separated by no more than a few hours, to facilitate administering a large volume of material or to minimize
fluctuations in blood levels of the test article.
Two ways in which the test may be performed are:
z Animals are treated with the test substance once, or twice at an interval of not more than 24 hours.
Samples of bone marrow are taken at least twice between 24 and 48 hr after the last dose, with
appropriate interval(s) between samples. The use of sampling times earlier than 24 hours after
treatment should be justified. Samples of peripheral blood are taken at least twice between 36 and 72
hours after the last treatment, with appropriate interval(s) between samples. When a positive response
is recognized at one sampling time, additional sampling is not required.
z If three or more daily treatments are used (e.g., three or more treatments at 24 hour intervals),
samples may be collected once no later than 24 hours following the final treatment for the bone marrow
and once no later than 40 hours following the final treatment for the peripheral blood.(12), (20)
Additional sampling times may be used, when relevant and scientifically justified.
If a dose range finding study is performed because there are no suitable data available, it should be
performed in the same laboratory, using the same species, strain, sex, and treatment regimen to be used in
the main study. (7) If there is toxicity, three dose levels should be used for the first sampling time. These dose
levels should cover a range from clear toxicity to little or no toxicity. At the later sampling time only the
highest dose needs to be used. The highest dose is defined as the dose producing signs of toxicity such that
higher dose levels, based on the same dosing regimen, would be expected to produce lethality. Substances
with specific biological activities at low non-toxic doses (such as hormones and mitogens) may be exceptions
to the dose-setting criteria and should be evaluated on a case-by-case basis. The highest dose may also be
defined as a dose that produces some indication of toxicity of the bone marrow (e.g., a reduction in the
proportion of immature erythrocytes among total erythrocytes in the bone marrow or peripheral blood).
If no observable toxic effects result from a single treatment with one dose level of at least 2000 mg/kg body
weight, or from two treatments on the same day, and if genotoxicity would not be expected based upon data
from structurally related substances, then a full study using 3 dose levels may not be necessary. For studies
of a longer duration, the limit dose is 2000 mg/kg/body weight/day for treatment up to 14 days, and 1000
mg/kg/body weight/day for treatment longer than 14 days. Expected human exposure may indicate the need
for a higher dose level to be used in the limit test.
The test substance is usually administered by gavage using a stomach tube or a suitable intubation cannula,
A. Number and Sex of Animals
B. Treatment Schedule
C. Dose Levels
D. Limit Test
E. Administration of Doses
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or by intraperitoneal injection. Other routes of exposure may be acceptable where they can be justified. The
maximum volume of liquid that can be administered by gavage or injection at one time depends on the size of
the test animal. The volume should not exceed 2 ml/100g body weight. The use of volumes higher than these
must be justified. Except for irritating or corrosive substances, which will normally reveal exacerbated effects
with higher concentrations, variability in test volume should be minimized by adjusting the concentration to
ensure a constant volume at all dose levels.
Bone marrow cells are usually obtained from the femurs or tibias immediately following sacrifice. Commonly,
cells are removed from femurs or tibias, prepared and stained using established methods. Peripheral blood is
obtained from the tail vein or other appropriate blood vessel. Blood cells are immediately stained supravitally
(4),(5),(14) or smear preparations are made and then stained. The use of a DNA specific stain (e.g., acridine
orange (15) or Hoechst 33258 plus pyronin-Y(30) ) can eliminate some of the artifacts associated with using a
non-DNA specific stain. This advantage does not preclude the use of conventional stains (e.g., Giemsa).
Additional systems (e.g., cellulose columns to remove nucleated cells (36) ) can also be used provided that
these systems have been shown to work adequately for micronucleus preparation in the laboratory.
The proportion of immature among total (immature + mature) erythrocytes is determined for each animal by
counting a total of at least 200 erythrocytes for bone marrow and 1000 erythrocytes for peripheral blood.(9)
All slides, including those of positive and negative controls, should be independently coded before microscopic
analysis. At least 2000 immature erythrocytes per animal are scored for the incidence of micronucleated
immature erythrocytes. Additional information may be obtained by scoring mature erythrocytes for
micronuclei. When analyzing slides, the proportion of immature erythrocytes among total erythrocytes should
not be less than 20% of the control value. When animals are treated continuously for 4 weeks or more, at
least 2000 mature erythrocytes per animal can also be scored for the incidence of micronuclei. Systems for
automated analysis (image analysis or flow cytometric analysis of cell suspensions) are acceptable alternatives
to manual evaluation if appropriately justified and validated relative to classical microscopic scoring. (12)
Published information based on studies in mice, rats, hamsters, swine, dogs, nonhuman primates, and
humans (3),(6),(18),(28),(31),(32),(39),(40),(45) indicate that spontaneous and induced frequencies of
micronucleated erythrocytes are similar in most mammalian species, and suggests that measurement of the
incidence of micronucleated immature erythrocytes in the bone marrow is appropriate for assessing
chromosomal or spindle damage in those species studied to date. Appearance and disappearance of
micronucleated erythrocytes in the bone marrow is a function of the kinetics of erythrogenesis and the
lifespan of erythrocytes in each species, and therefore dosing and sampling regimens must be modified in
accordance with the appropriate parameters of erythrocyte kinetics for each species. Species other than mice
or rats may be used when appropriate, but the following information should be included:
z Justification of the selected species, and the dosing and sampling schedules used in relation to the
kinetics of erythropoiesis and the lifespan of erythrocytes in the species used;
z Evidence that the spontaneous micronucleus frequency is consistent with published information, and/or
consistent within the laboratory conducting the study;
z Evidence that known genotoxicants produce an increase in micronucleus frequency in the species used,
and reference values for the magnitude of the response induced;
z Impact of splenic selective removal of micronucleated cells from peripheral blood (when the latter serves
as the tissue being monitored).
Individual animal data should be presented in tabular form. The experimental unit is the animal. The number
of immature erythrocytes scored, the number of micronucleated immature erythrocytes, and the number of
immature among total erythrocytes should be listed separately for each animal analyzed. When animals are
treated continuously for 4 weeks or more, the data on mature erythrocytes should also be given if it is
collected. The proportion of immature among total erythrocytes and, if considered applicable, the percentage
of micronucleated mature erythrocytes should be given for each animal. If there is no evidence for a
F. Bone Marrow/Blood Preparation
G. Analysis
VII. Procedure for Species Other than Rats and Mice
VIII. Data and Reporting
A. Treatment Results
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difference in response between the sexes, the data from both sexes may be combined for statistical analysis.
There are several criteria for determining a positive result, such as a dose-related increase in the number of
micronucleated cells or a clear increase in the number of micronucleated cells in a single dose group at a
single sampling time. Statistical methods should be used to evaluate the test results.(24),(35) The statistical
criteria for a positive, negative, or equivocal result should be stated clearly in the protocol. Since biological
factors may modify the interpretation, statistical significance should not be the only determining factor for
reaching a conclusion. Equivocal results should be clarified by further testing, using a modification of
experimental conditions if appropriate.
Although most experiments will give clearly positive or negative results, in rare cases the data set will
preclude making a definite judgement about the activity of the test substance. Results may remain equivocal
or questionable regardless of the number of times the experiment is repeated.
Positive results in the micronucleus test indicate that a substance induces micronuclei, which are the result of
chromosomal damage or damage to the mitotic apparatus in the erythroblasts of the test species. Negative
results indicate that, under the test conditions, the test substance does not produce chromosomal or spindle
damage leading to the formation of micronuclei in the immature erythrocytes of the test species.
The likelihood that the test substance or its metabolites reach the general circulation or specifically the target
tissue (e.g., systemic toxicity) should be discussed. The demonstration of adequate target tissue exposure in
a negative micronucleus assay is a particularly important consideration when there is positive evidence of
genotoxicity in one or more other test systems.
The test report should also include the following information:
z identification data and CAS no., if known
z physical nature and purity
z physicochemical properties relevant to the conduct of the study
z stability of the test substance, if known
z justification for choice of vehicle
z solubility and stability of the test substance in the solvent/vehicle, if known
z times dosing solutions were prepared and used (or interval between preparation and usage), and
storage conditions
z data that verifies the concentration of the dosing solution, if available
z species/strain used, including justification
z number, age and sex of animals
z source, housing conditions, diet, etc.
z individual weight of the animals at the start of the test, including body weight range, mean and standard
deviation for each group
z information regarding the potential influence of splenic selection on the incidence of micronucleated cells
in the peripheral blood, if applicable
z positive and negative (vehicle/solvent) control data
z data from range-finding study, if conducted
z rationale for dose level selection
B. Evaluation and Interpretation of Results
C. Test Report
1. Test Substance
2. Solvent/Vehicle
3. Dosing solutions
4. Test animals
5. Test Conditions
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z details of test substance preparation
z details of the administration of the test substance
z rationale for route of administration and dosing regimen
z methods for verifying that the test substance reached the general circulation and/or target tissue, if
applicable
z conversion from diet/drinking water test substance concentration (ppm) to the actual dose (mg/kg body
weight/day), if applicable
z details of food and water quality
z detailed description of treatment and sampling schedules
z methods of slide preparation
z methods for measurement of toxicity
z criteria for scoring micronucleated immature erythrocytes and, if appropriate and applicable, mature
erythrocytes
z number of cells analyzed per animal
z criteria for considering studies as positive, negative or equivocal
z signs of toxicity
z proportion of immature erythrocytes among total erythrocytes
z number of micronucleated immature erythrocytes among total immature erythrocytes, given separately
for each animal
z if appropriate and applicable, number of micronucleated mature erythrocytes among total mature
erythrocytes, given separately for each animal
z mean ± standard deviation of micronucleated immature and, if applicable, mature erythrocytes per
group
z dose-response relationship, where possible
z statistical analyses and justification for method applied, with appropriate literature citation
z concurrent and historical negative control data
z concurrent and historical positive control data
Micronuclei can be formed by acentric fragments or entire chromosomes lagging in mitosis. These latter
micronuclei were first recognized by their large size,(49) by C-banding(47) or by measurement of DNA content.
(46) However, these methods were not very reliable. Therefore, two molecular cytogenetic methods were
developed to identify the presence of centromeres in micronuclei and thereby differentiate between
micronuclei of clastogenic and aneugenic origin: (12) 1) immunofluorescent CREST-staining and 2) fluorescence
in situ hybridization (FISH) with pancentromeric DNA-probes. When it is mechanistically important to
determine the presence of the kinetochore or centromere in the micronuclei, these methods can be applied.
The CREST method applied to the bone marrow micronucleus test is described in detail by Miller and Adler. (33)
Cells on slides (normal bone marrow smears) are fixed, dehydrated, incubated in two steps with SDS and
Triton-X, and then stained with antibody. DNA is counterstained by Hoechst 33258.
With FISH, the minor satellite DNA-probe which hybridizes close to the centromere(43) is used to identify the
centromeric region, if present. A method for FISH with the centromeric DNA-probes has been described by
Pinkel et al.(34) This method can be applied to flow sorted micronuclei-containing erythrocytes(10) or to
isolated micronuclei obtained from peripheral blood samples.(13)
In control slides, the rate of labeled micronuclei containing the centromeric region is about 50%. (43)
Approximately 70% of micronuclei induced by known aneugens (colchicine and vinblastine) are labeled,(33)
whereas those induced by clastogens (hydroquinone and mitomycin C) only show 5-15% labeled micronuclei.
6. Results
7. Discussion of the Results
8. Conclusion
XI. Addendum: Identification of Micronuclei Derived from Acentric Fragments vs. Centromeric
Chromosomes
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(33) To characterize the relative clastogenic vs aneugenic activity of a chemical, it is useful to use as an index
the number of micronucleated polychromatic erythrocytes per 1000 polychromatic erythrocytes that contain
the centromeric region. (42)
The main deficiency in the FISH methods described to date is that they do not differentiate between
normochromatic and polychromatic erythrocytes.(12) Thus, only preparations in which a large fraction of the
micronuclei present are induced by the test article are suitable for analysis. For example, peripheral blood
samples from experiments with acute exposures in adult animals are essentially never suitable for analysis
because the target cell population (immature erythrocytes) is only 3-5% of the erythrocytes in the sample.
In conclusion, CREST- or FISH-labeling are considered reliable methods to detect aneugenic properties of
chemicals in the in vivo micronucleus assay, provided attention is paid to ensuring that appropriate samples
are used for analysis. (12) However, the complexity of the current methods limits their use to those cases in
which a chemical is suspected of causing spindle impairment (e.g., due to the presence of large micronuclei,
the induction of polyploidy, etc.) or when there are other specific reasons to obtain this mechanistic
information.
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Screening. Mutation Res. 127:169-174.
40. 	Schlegel, R., MacGregor, J.T. and Everson, R.B. (1986). Assessment of Cytogenetic Damage by
Quantitation of Micronuclei in Human Peripheral Blood Erythrocytes. Cancer Res. 46:3717-3721.
41. 	Schmid, W. (1975). The Micronucleus Test. Mutation Res. 31:9-15.
42. 	Schriever-Schwemmer G. and Adler I.-D. (1997). Differentiation of Micronuclei in Mouse Bone Marrow
Cells: A Comparison between CREST Staining and Fluorescence In Situ Hybridization with Centromeric
and Telomeric DNA Probes. Mutagenesis 9:333-340.
43. 	Schriever-Schwemmer G., Kliesch U., and Adler I.-D. (1994). Extruded Micronuclei Induced by
Colchicine or Acrylamide Contain Mostly Lagging Chromosomes Identified in Paintbrush Smears by Minor
and Major Mouse DNA Probes. Mutagenesis 12:201-207.
44. 	Tice, R.R., Furedi-Machacek, M., Satterfield, D.N.A., Udumudi, A., Vasquez, M., Dunnick, J.K. (1998).
Measurement of Micronucleated Erythrocytes and DNA Damage During Chronic Ingestion of
Phenolphthalein in Transgenic Female Mice Heterozygous for the p53 Gene. Environ. Molec. Mutagen.
31:113-124.
45. 	Tsuchimoto, T. and Matter, B.E. (1979). In Vivo Cytogenetic Screening Methods for Mutagens, with
Special Reference to the Micronucleus Test. Arch. Toxicol. 42:239-248.
46. 	Vanderkerken K., Vanparys Ph., Verschaeve L., and Kirsch-Volders M. (1989). The Mouse Bone Marrow
Micronucleus Assay Can be Used to Distinguish Aneugens from Clastogens. Mutagenesis 4:6-11.
47. 	Verschaeve L., Vanderkerken K., and Kirsch-Volders M. (1988). C-banding as a Simple Tool to
Discriminate between Micronuclei Induced by Clastogens and Aneugens. Stain Technol. 63:351-354.
48. 	Witt, K.L., Gulati, D.K., Kaur, P., Shelby, M.D. (1995). Phenolphthalein: Induction of Micronucleated
Erythrocytes in Mice. Mutation Res. 341:151-60.
49. 	Yamamoto K.I. and Kikuchi Y. (1980). A Comparison of Diameters of Micronuclei Induced by Clastogens
and by Spindle Poisons. Mutation Res. 71:127-131.
50. 	Yamamoto K.I. and Kikuchi Y. (1981). Studies on Micronuclei Time Response and on the Effects of
Multiple Treatments of Mutagens on Induction of Micronuclei. Mutation Res. 90:163-173.
Links on this page:
Redbook 2000: IV.C.1.d Mammalian Erythrocyte Micronucleus Test
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Draft
Chapter IV. Guidelines for Toxicity Tests
IV C 2. Acute Oral Toxicity Tests
Acute toxicity tests can provide preliminary information on the toxic nature of a material for which no
other toxicology information is available. Such information can be used to:
4 deal with cases of accidental ingestion of a large amount o f the material (e.g., for poison control
information);
4 determine possible target organs that should be scrutinized and/or special tests that should be
conducted in repeated-dose toxicity tests; 1 and
4 select doses for short-term and subchronic toxicity tests when no other toxicology inform ation is
availab le.
In most acute toxicity tests, each test animal is adm inistered a single (relatively high) dose of the test
substance, observed for 1 or 2 wee ks for signs of treatm ent-related effects, then necrop sied. Some acute to xicity
tests (such as the "classical" LD50 test) are designed to determine the mean lethal dose of the test substance. The
median lethal dose (or LD50) is defined as the dose of a test substance that is lethal for 50% o f the animals in a
dose group. LD50 values have b een used to compare relative acute hazards of industrial chem icals, especially
when no other toxicology data are available for the chemicals. However, many imp ortant observations of toxicity
are not represented by LD50 values or by slopes of dose-response curves for lethality. For example, information
abo ut morbidity and pathogenesis m ay have more toxicological significance than mortality, and these endpo ints
also should b e evaluated in sho rt term toxicity tests.
The Agency does not recommend that petitioners determine the median lethal dose (or LD50) for direct
food additives or color additives used in food . However, if a petitioner decides to conduc t an acute oral toxicity
test, alternative test protocols can provide useful information about the acute toxicity of a substance.3 These
protocols generally use fewer animals, and are thus more cost efficient, than tests designed to determine LD50s.2
The following guidelines should help the petitioner design acute oral toxicity tests when the petitioner has decided
that such information is useful:
4 The m ain focus of the acute toxicity test should be on ob serving the symptoms and recovery of the test
animals, rather than on determining the median lethal dose (LD50) of the substance.
4 The rat often is used as the animal mode l in acute to xicity tests, but other sp ecies also may be use d.
4 Often only one sex is studied in an acute toxicity test; generally, the female is assumed to be more
sensitive to the acute toxic effects of chemicals than the male.1
4 Before deciding on the dose of a test compound that will be used in studying its acute toxicity, the
compo und's chemical and physical characteristics (including molecular weight, partition coefficient, and
the toxicity of related che micals) should be considered; othe rwise, oral toxicity--including lethality--
caused by re latively large dose s of a chemical may have no biological relevanc e to the chem ical's effects
at lower doses. 1,5
The following brief descriptions of oral toxicity tests may help the petitioner choose a test that meets his
need s; detailed information abo ut each type of test is availab le in the referenced material.
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a. Limit Tests
To d etermine the acute toxicity of a new food additive that is not expected to be particularly toxic, 5 gm
(or ml) of the compound/kg body weight of the test animal should be administered orally by gavage to several
(perhaps 5) animals that have been fasted (overnight for rats, 4 hours for mice). Test animals should be observed
closely for up to 14 days; symptoms of toxicity and recovery should be noted. Gross and histopathological
examination of the test animals at the end of the study may help identify toxic effects on target organs. If no
animals die as a result of this dose, there is no need to test higher dosages. The acute toxicity of the compound can
then be expressed as being greater than 5 gm (or ml)/kg body weight of the test animal. This method is called the
"limit test." In general, 5 gm or 5 ml of the test substance/kg body weight is the practical upper limit for the
amo unt of test m aterial that can be adm inistered in one oral gavage dose to a rodent.
If there are deaths following administration of an ac ute dose o f 5 gm/kg bo dy weight, then a lower d ose
should be administered to several (perhaps 5) animals and the results evaluated as discussed above. For
com pounds expected to be acutely toxic at 5 gm /kg bo dy weight, it would be wise to select a low er initial "limit"
dose.
b. Dose-Pr obing Tests
Dose-probing acute toxicity protocols may have value when the petitioner has no preliminary information
abo ut the test sub stance that would help him select ap propriate dose s for toxicity studies. In a dose-pro bing acute
toxicity test, one animal per each of 3 widely spaced dosages should be used and a sufficient observation period
should follow administration of the doses. Subsequent toxicity studies may be based on the results of the dose-
probing study. 1 Variations o f dose-prob ing acute toxicity stud ies are d escribed in the literature. 6,7 Other methods
of determining appropriate doses for longer-term toxicity studies include a simple test wherein 3 or 4 doses are
each administered to 1 or 2 test animals and the animals are ob served for up to 1 4 days. If some of the animals
die, one can estimate an ap proximate median lethal dose, termed AL D. 8
c. Up-an d-Dow n Tests
The "up-and-down" procedure involves dosing animals one at a time: First one animal at one dose, then
another animal one or two days later at a higher dose (if the first animal survives) or a lower dose (if the first animal
dies). This process continues until the approximate LD50 has been determined. One disadvantage to this test is the
length of the study. Each animal should be observed for at least seven days after dosing so that delayed deaths can
be reco rded. H owever, this method usually requires o nly six or eight test animals as comp ared with the 40 to 50 test
animals that may be used in the "classical" LD50 test. 9-11
d. Pyram iding Tests
Pyramiding studies involve a minimum number of animals: Two animals are given successively increasing
doses of the test substance o n alterna te days until an acutely toxic d ose o r some practical up ward limit is reached.
This test does not yield a lethality curve and often is used to assess acute toxicity in non-rodents. This test, although
more like a short-term, repeated dose toxicity study than a true acute toxicity study, can provide useful preliminary
information on the toxic nature of a new material for which no other toxicology information is available.
References
1. Gad, S.C . and C hengelis, C.P . (198 8) In, Acute toxicity testing perspectives and horizons. (S.C. Gad and
C.P. Chengelis ed s.) The Telford Press. Cald well, N.J. pp. 2-4a, 318b, 156c, 165-167d, 159e.
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2. Food and Drug Administration [FDA] (1988) LD50 Test Policy. Fed.Reg. 53 (October 11 Issue):39650-
39651.
3. Litchfield, J.T., Jr., W ilcoxon, F. (19 49) A simplified method of evaluating dose-effect experiments.
J.Pharmacol.Exp.Therap. 96:113.
4. Anonymous. (1989) Comments on the LD50 and acute eye and skin irritation tests. In, a position paper
reported by the Animals in Research Committee of the Society of Toxicology (SOT ) and approved b y the
SO T C ounc il. Fund.Appl.Toxicol. 13:621-623.
5. Zbinden, G. and Flury-Roversi, M. (1981) Significance of the LD50 test for the toxicological evaluation
of chemical substances. Arch.Toxicol. 47:77-99.
6. Lorke, D. (198 3) A new approach to practical acute toxicity testing. Arch.Toxicol. 54:275-287.
7. Schutz, E. & Fuchs, H. (1 982 ). A new approach to minimizing the numb er of animals use d in acute
toxicity testing and o ptimizing the info rmatio n of test results. Arch.Toxicol.51:197-220.
8. Deichma nn, W .B. and LeBlanc, T .J. (1943) Determination o f the app roxim ate lethal dose with about six
anima ls. J.Indust. Hygiene Toxicol. 25:415-417.
9. Bruce, R.D. (1985 ) An up-and -down pro cedure for acute to xicity testing. Fund.Appl.Toxicol. 5:151-157.
10. Gad, S.C., Smith, A.C., Cramp, A.L., Gavigan, F.A., and Derelanko, M .J. (1984) Innovative Designs and
Practices for Acute System ic Toxicity Studies. Drug Chem.Toxicol. 7:423-434.
11. Muller, H. and Kley, H.P. (1982) Retrospective study on the reliability of an "approximate LD50,"
determined with a small number o f animals. Arch.Toxicol. 51:189-196.
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Short-term toxicity studies with rodents are generally conducted for 14 or 28 days (one month). Results of
these studies (1) can help predict appropriate doses of the test substance for future subchronic or chronic
toxicity studies, (2) can be used to determine NOELs for some toxicology endpoints, and (3) allow future
studies in rodents to be designed with special emphasis on identified target organs. Guidelines for short-term
toxicity studies with non-rodents are discussed in IV.C.3b. Sponsors/submitters of petitions/notifications are
encouraged to also become familiar with the Guidance for Reporting Results of Toxicity Studies (Chapter
IV.B.2.), Pathology Considerations in Toxicity Studies (Chapter IV.B.3.), and Statistical Considerations in
Toxicity Studies (Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to the 1993 draft "Redbook II" version of this section have been made following
consultation with other authoritative guidelines and publications 1-8
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Redbook 2000: IV.C.3.a Short-Term Toxicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.3.a. Short-Term Toxicity Studies with Rodents
I. Good Laboratory Practice
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.3.a Short-Term Toxicity Studies with Rodents
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Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"8
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines.
These guidelines are for studies with rodents (usually rats and mice); if other species are used, modifications
of these guidelines may be necessary. Both male and female test animals, that are healthy and have not been
subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies.The selection of the use of inbred, out-bred, or hybrid rodent strains for toxicity tests should be based
upon the scientific questions to be answered. Additionally, it is important that test animals come from well-
characterized and healthy colonies. FDA encourages petitioners and notifiers to consult with Agency scientists
before toxicity testing is begun if they have questions about the appropriateness of a particular species, strain,
or substrain.
Testing should be performed on young animals, with dosing beginning as soon as possible after weaning, but
no later than 6 to 8 weeks of age, and following an acclimation period of at least 5 days.
Equal numbers of males and females of each species and strain should be used for the test. For short-term
toxicity studies of 30 days duration or less, experimental and control groups should have at least 10 rodents
per sex per group. The number of animals that survive until the end of the study must be sufficient to permit
a meaningful evaluation of toxicological effects.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal must be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tatoo).
Animals should be housed one per cage (single-caged). This recommendation reflects three principal
concerns:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
In general, feed and water should be provided ad libitum to rodents in toxicity studies, and the diets for these
studies should meet the nutritional requirements of the species 4-7 for normal growth and reproduction. Unless
special circumstances apply which justify otherwise, care should be taken to ensure that the diets of the
compound treated groups of animals are isocaloric (equivalent in caloric density) with and contain the same
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Rodent Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
H. Diet:
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levels of nutrients (e.g., fiber, micronutrients) as the diets of the control group. Unrecognized or inadequately
controlled dietary variables may result in nutritional imbalances or caloric deprivation that could confound
interpretation of the toxicity study results (e.g., lifespan, background rates of tumor incidences) and alter the
outcome and reproducibility of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test article doses than
expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed groups
to compensate for the differences in energy and nutrient content of the high dose diets. Such circumstances
make it especially important that feed consumption of these animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of litter-
mate weanling rats of the same sex and approximate size are selected and fed the control or the experimental
diet. Animals should be single-caged so that feed consumption can be determined daily, and the control
animal is then fed an amount of food equal to that which the paired experimental animal ate on the preceding
day. If the test substance is non-nutritive and composes a significant proportion of the diet, the pair-fed
control animals should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of
diet as the paired experimental animal. Additionally, the study should include a second group of control
animals fed ad libitum to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term and subchronic toxicity studies because of batch to batch variations in diet
composition (e.g., fiber, mineral, vitamins, isoflavones) in some of the commonly used laboratory animal
chows. The use of these semi-purified diets, however, may not be advisable in long-term and reproductive
studies due to inadequate historical data related to their influences on animal survival and toxicological
endpoints. For example, loss of necessary but unidentified micronutrients in the semipurified diet may
interfere with normal reproduction.
Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993 draft
"Redbook II"
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day; if this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. If the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
I. Assignment of Control and Compound Treated Animals:
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Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
For example, under normal circumstances, mortality in the control group should not exceed 10%.
Adequate animal husbandry practices should result in considerably less than 10% of animals and tissues or
organs lost to a study because of autolysis. Autolysis in excess of this standard may be cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are similar in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
Animals should be exposed to the test substance 7 days per week for the duration of the study (from 2 to 4
consecutive weeks).
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (for
example, in soft drinks or beer), or if administration in the diet is inappropriate for other reasons. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size; for rodents, the volume ordinarily should not exceed 1
ml/100 g body weight. If the gavage vehicle is oil (see Chapter IV.B.5.b. in the 1993 draft "Redbook II"),
then the volume should be no more than 0.4 ml/100 g of body weight, and the use of a low-fat diet
should be considered. If the test substance must be given in divided doses, all doses should be
administered within a 6 hour period. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished.
A minimum of three dose levels of the test substance, per sex, should be used, however 4 or 5 dose levels of
the test substance is preferred. A concurrent control group should be included.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in section "II Test Animals, H. Diet" above.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 9
C. Dose groups:
1. Selection of Treatment Doses:
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
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Routine cage-side observations should be made on all animals at least once or twice a day throughout the
study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10.), conducted inside
and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions and autonomic activity (e.g.,
lacrimation, pilorection, pupil size, unusual respiratory pattern). Additionally, changes in gait, posture and
response to handling, as well as the presence of clonic or tonic movements, stereotypes (e.g., excessive
grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should be
recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Test animals should be weighed at least once a week. Feed consumption (or water consumption if the test
substance is administered in the drinking water) should be measured every week during the short-term
toxicity test. Petitioners/notifiers should also attempt to quantify spillage of feed by test animals, and to
determine if spillage is greater with test diets than with control diets. Appropriate discussions of feed spillage
should be included in the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: 	This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
in the study.
2. 	Hematology: 	For rodents, hematologic tests should be performed on 10 animals of each sex per
group. Sampling of test animals should be conducted during the first two weeks on study (receiving
treatment) and at the end of the study. The determination of the first sampling time point should be
based on the expected time of initial toxicological effects on the organ systems. Ideally, samples should
be obtained from the same animals during the study and at termination. Blood should be drawn at
approximately the same time each sampling day and blood samples should be analyzed individually, and
not pooled.
1. 	The following determinations are recommended:
1. 	hematocrit
2. 	hemoglobin concentration
3. 	erythrocyte count
4. 	total and differential leukocyte counts
5. 	mean corpuscular hemoglobin
6. 	mean corpuscular volume
7. 	mean corpuscular hemoglobin concentration
8. 	and a measure of clotting potential (such as clotting time, prothrombin time, thromboplastin
A. Observations of Test Animals:
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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time, or platelet count).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
3. 	Clinical Chemistry: 	Ideally, the same animals should be sampled at blood collection time points. For
rodents, clinical chemistry tests should be performed on 10 animals of each sex per group. Sampling of
test animals should be conducted during the first two weeks on study (receiving treatment) and at the
end of the study. The determination of the first sampling time point should be based on the expected
time of initial toxicological effects on the organ systems. Blood samples should be drawn at the end of
the fasting time and before feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Blood should be drawn at approximately the same time on each
sampling day, and blood samples should be analyzed individually, and not pooled.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, carbohydrate metabolism, and liver and kidney function. Specific determinations should
include:
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
1. 	However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the
test compound may warrant the consideration of alternative tests. Appropriate justification for
alternative tests should be presented in study reports.
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1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day10 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: Timed urine volume collection should be conducted during the last week of the study. For
rodents, these tests should be performed on 10 animals of each sex in each group. The volume of urine
collected, specific gravity, pH, glucose, and protein should be determined as well as conducting a
microscopic evaluation of urine for sediment and presence of blood/blood cells.11
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
all short-term toxicity studies with rodents (preferably rats). The neurotoxicity screen should be age
appropriate and would typically include: (1) a specific histopathological examination of tissue samples
representative of major areas of the brain, spinal cord, and peripheral nervous system (see organs and
tissues listed below under VI.C. Preparation of Tissues for Microscopic Examination) and (2) a functional
battery of quantifiable observations and manipulative tests selected to detect signs of neurological,
behavioral, and physiological dysfunctions. This functional battery is also referred to as an expanded set
of clinical evaluations and is described more fully in section V.A. Observations of Test Animals in this
Chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Short-term toxicity study reports should include an assessment of the potential for the test substance to
adversely affect the structural or functional integrity of the nervous system. This assessment should
evaluate data from the neurotoxicity screen and other toxicity data from the study, as appropriate.
Based on this assessment, the petitioner should make an explicit statement about whether or not the
test substance presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed
appropriate. FDA recommends that additional neurotoxicity testing not be undertaken without first
consulting with the Agency.
6. 	Immunotoxicity: Results from tests that are included in the list of primary indicators for immune
toxicity (see Chapter V.C. of the 1993 draft "Redbook II") should also be evaluated as part of an
immunotoxicity screen. Reports of short-term toxicity tests should include an assessment of the
potential for the test substance to adversely affect the immune system. This assessment should evaluate
data from the list of primary indicators included in the immunotoxicity screen and other toxicity data
from the study, as appropriate. Based on this assessment, the petitioner/notifier should make an explicit
statement about whether or not the test substance presents a potential immunotoxic hazard which
requires further immunotoxicity testing. Additional immunotoxicity tests are discussed in Chapter V. C.
of the 1993 draft "Redbook II", but should not be undertaken without first consulting with the Agency.
VI. Necropsy and Microscopic Examination
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All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	Harderian gland
15. 	heart
16. 	ileum
17. 	jejunum
18. 	kidneys
19. 	liver
20. 	lung (with main-stem bronchi)
21. 	lymph nodes (1 related to route of administration and 1 from a distant location)
22. 	mammary glands
23. 	nasal turbinates
24. 	ovaries and fallopian tubes
25. 	pancreas
26. 	pituitary
27. 	prostate
28. 	rectum
29. 	salivary gland
30. 	sciatic nerve
31. 	seminal vesicle
32. 	skeletal muscle
33. 	skin
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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34. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
35. 	spleen
36. 	stomach
37. 	testes
38. 	thymus (or thymic region)
39. 	thyroid/parathyroid
40. 	trachea
41. 	urinary bladder
42. 	vagina
43. 	Zymbal's gland
44. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V. C.) for all animals.
1. 	EPA Health Effects Test Guidelines OPPTS 870.3050, 28-Day Oral Toxicity in Rodents, July 2000
2. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 28-day Oral Toxicity Study in Rodents,
407, July 1995
3. 	Kurt Weingand et al, Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety Studies,
Fundamental and Applied Toxicology 29, pp 198-201, 1996
4. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995.
5. 	Nutrient Requirements of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
6. 	Nutrient Requirements of Swine: 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
7. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
8. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
9. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
10. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
11. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor & Francis, Philadelphia, PA, pp. 520-533
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
Links on this page:
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Short-term toxicity studies with non-rodents (usually dogs) are generally conducted for 14 or 28 days (one
month). Results of these studies (1) can help predict appropriate doses of the test substance for future
subchronic or chronic toxicity studies, (2) can be used to determine NOELs for some toxicology endpoints, and
(3) allow future studies in rodents and non-rodents to be designed with special emphasis on identified target
organs. Guidelines for short-term toxicity studies with rodents are discussed in IV.C.3a. Sponsors/submitters
of petitions/notifications are encouraged to also become familiar with the Guidance for Reporting Results of
Toxicity Studies (Chapter IV.B.2.), Pathology Considerations in Toxicity Studies (Chapter IV.B.3.), and
Statistical Considerations in Toxicity Studies (Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to the 1993 draft "Redbook II" version of this section have been made following
consultation with other authoritative guidelines and publications 1-7
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Redbook 2000: IV.C.3.b Short-Term Toxicity Studies with Non-Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.3.b. Short-Term Toxicity Studies with Non-Rodents
I. Good Laboratory Practice
II. Test Animals
Food
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Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"7
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines.
These guidelines are for studies with non-rodents (usually dogs); if other species are used, modifications of
these guidelines may be necessary. Both male and female test animals, that are healthy and have not been
subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting species and strains for toxicity studies. Test animals
should be selected that are likely to survive the recommended duration of the study. It is important that test
animals come from well-characterized and healthy colonies. FDA encourages petitioners and notifiers to
consult with Agency scientists before toxicity testing is begun if they have questions about the
appropriateness of a particular species or strain.
Testing should be performed on young animals, with dosing beginning as soon as possible after weaning, and
following an acclimation period of at least 5 days. Testing should begin when dogs are no older than 4 to 6
months of age.
Equal numbers of males and females of each species and strain should be used for the test. For short-term
toxicity studies of 30 days duration or less, experimental and control groups should have at least 4 dogs per
sex per group. If the study will be used to determine appropriate doses for longer-term dog studies, but will
not be used to determine a NOEL for the test substance, experimental and control groups may have 2 dogs
per sex per group. The number of animals that survive until the end of the study must be sufficient to permit
a meaningful evaluation of toxicological effects.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal must be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tatoo).
Animals should be housed one per cage or run (single-caged). This recommendation reflects three principal
concerns:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
Diets for short-term studies should meet the nutritional requirements of the species3-6 for normal growth and
reproduction. In general, water should be provided ad libitum . Unless special circumstances apply which
justify otherwise, care should be taken to ensure that the diets of the compound treated groups of animals are
isocaloric (equivalent in caloric density) with and contain the same levels of nutrients (e.g., fiber,
A. Care, Maintenance and Housing:
B. Selection of Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
H. Diet:
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micronutrients) as the diets of the control group. Unrecognized or inadequately controlled dietary variables
may result in nutritional imbalances or caloric deprivation that could confound interpretation of the toxicity
study results (e.g., lifespan, background rates of tumor incidences) and alter the outcome and reproducibility
of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. It is important that feed consumption of animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of animals
of the same sex, age, and approximate size are selected and fed the control or the experimental diet. Animals
should be single-caged so that feed consumption can be determined daily, and the control animal is then fed
an amount of food equal to that which the paired experimental animal ate on the preceding day. If the test
substance is non-nutritive and composes a significant proportion of the diet, the pair-fed control animals
should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of diet as the
paired experimental animal. Additionally, the study should include a second group of control animals fed the
normal ration amount to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term toxicity studies because of batch to batch variations in diet composition (e.g., fiber,
mineral, vitamins, isoflavones) in some of the commonly used laboratory animal chows. The use of these
semi-purified diets, however, may not be advisable in long-term and reproductive studies due to inadequate
historical data related to their influences on animal survival and toxicological endpoints. For example, loss of
necessary but unidentified micronutrients in the semipurified diet may interfere with normal reproduction.
FDA recommends reviewing the diet section in IV.C.3.a. when non-rodents (e.g., rabbits) are to be fed ad
libitum. Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993
draft "Redbook II"
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day.
Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
Adequate animal husbandry practices should be employed so that tissues and/or organs are not lost to a
study because of autolysis.
I. Assignment of Control and Compound Treated Animals:
J. Mortality:
K. Autolysis:
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Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are similar in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
Animals should be exposed to the test substance 7 days per week for the duration of the study (from 2 to 4
consecutive weeks).
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (for
example, in soft drinks or beer), or if administration in the diet is inappropriate for other reasons. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished. (See additional information in
Chapter IV.B.5. in the 1993 draft "Redbook II".)
A minimum of three dose levels of the test substance, per sex, should be used, however 4 or 5 dose levels of
the test substance is preferred. A concurrent control group should be included.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in section "II Test Animals, H. Diet" above.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 8
Routine cage-side observations should be made on all animals at least once or twice a day throughout the
study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10), conducted inside
C. Dose groups:
1. Selection of Treatment Doses:
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
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and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions or other evidence of autonomic
activity (e.g., lacrimation, piloerection, pupil size, unusual respiratory pattern). Additionally, changes in gait,
posture and response to handling, as well as the presence of clonic or tonic seizures, stereotypes (e.g.,
excessive grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should
be recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Test animals should be weighed at least once a week. Feed consumption (or water consumption if the test
substance is administered in the drinking water) should be measured every week during the short-term
toxicity test. Petitioners/notifiers should also attempt to quantify spillage of feed by test animals, and to
determine if spillage is greater with test diets than with control diets. Appropriate discussions of feed spillage
should be included in the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: 	This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
in the study.
2. 	Hematology: 	For non-rodents (e.g., dogs and mini swine) hematologic tests should be performed on
all animals of each sex per group. Sampling of test animals should be conducted prior to initiation of
treatment, during the first two weeks on study (receiving treatment), and at the end of the study. The
determination of the second sampling time point should be based on the expected time of initial
toxicological effects on the organ systems. Blood should be drawn at approximately the same time each
sampling day, and blood samples should be analyzed individually, and not pooled.
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
3. 	Clinical Chemistry: 	For non-rodents (e.g., dogs and mini swine) hematologic tests should be
performed on all animals of each sex per group. Sampling of test animals should be conducted prior to
initiation of treatment, during the first two weeks on study (receiving treatment), and at the end of the
study. The determination of the second sampling time point should be based on the expected time of
initial toxicological effects on the organ systems. Blood samples should be drawn at the end of the
fasting time and before feeding. Fasting duration should be appropriate for the species and the analytical
tests to be performed. Blood should be drawn at approximately the same time on each sampling day,
and blood samples should be analyzed individually, and not pooled.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, carbohydrate metabolism, and liver and kidney function. Specific determinations should
include:
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
1. 	However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the
test compound may warrant the consideration of alternative tests. Appropriate justification for
alternative tests should be presented in study reports.
1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day9 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: Timed urine volume collection should be conducted during the last week of the study. For
non-rodents, the tests should be performed on all animals in the study. The volume of urine collected,
specific gravity, pH, glucose, and protein should be determined as well as conducting a microscopic
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evaluation of urine for sediment and presence of blood/blood cells.10
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
all short-term toxicity studies with non-rodents (preferably dogs or miniature swine). The neurotoxicity
screen should be age appropriate and would typically include: (1) a specific histopathological
examination of tissue samples representative of major areas of the brain, spinal cord, and peripheral
nervous system (see organs and tissues listed below under VI.C. Preparation of Tissues for Microscopic
Examination) and (2) a functional battery of quantifiable observations and manipulative tests selected to
detect signs of neurological, behavioral, and physiological dysfunctions. This functional battery is also
referred to as an expanded set of clinical evaluations and is described more fully in section V.A.
Observations of Test Animals in this chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Short-term toxicity study reports should include an assessment of the potential for the test substance to
adversely affect the structural or functional integrity of the nervous system. This assessment should
evaluate data from the neurotoxicity screen and other toxicity data from the study, as appropriate.
Based on this assessment, the petitioner should make an explicit statement about whether or not the
test substance presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed
appropriate. FDA recommends that additional neurotoxicity testing not be undertaken without first
consulting with the Agency.
6. 	Immunotoxicity: Results from tests that are included in the list of primary indicators for immune
toxicity (see Chapter V.C. of the 1993 draft "Redbook II") should also be evaluated as part of an
immunotoxicity screen. Reports of short-term toxicity tests should include an assessment of the
potential for the test substance to adversely affect the immune system. This assessment should evaluate
data from the list of primary indicators included in the immunotoxicity screen and other toxicity data
from the study, as appropriate. Based on this assessment, the petitioner/notifier should make an explicit
statement about whether or not the test substance presents a potential immunotoxic hazard which
requires further immunotoxicity testing. Additional immunotoxicity tests are discussed in Chapter V.C. of
the 1993 draft "Redbook II", but should not be undertaken without first consulting with the Agency.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	Harderian gland
15. 	heart
16. 	ileum
17. 	jejunum
18. 	kidneys
19. 	liver
20. 	lung (with main-stem bronchi)
21. 	lymph nodes (1 related to route of administration and 1 from a distant location)
22. 	mammary glands
23. 	nasal turbinates
24. 	ovaries and fallopian tubes
25. 	pancreas
26. 	pituitary
27. 	prostate
28. 	rectum
29. 	salivary gland
30. 	sciatic nerve
31. 	seminal vesicle (if present)
32. 	skeletal muscle
33. 	skin
34. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
35. 	spleen
36. 	stomach
37. 	testes
38. 	thymus (or thymic region)
39. 	thyroid/parathyroid
40. 	trachea
41. 	urinary bladder
42. 	vagina
43. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V.C. of the 1993 draft "Redbook II") for all animals.
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
1. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 28-day Oral Toxicity Study in Rodents,
407, July 1995
2. 	Kurt Weingand et al., 1996. "Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety
Studies", Fundamental and Applied Toxicology, 29, pp 198-201.
3. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995.
4. 	Nutrient Requirements of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
5. 	Nutrient Requirements of Swine: 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
6. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
7. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
8. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
9. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
10. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor & Francis, Philadelphia, PA, pp. 520-533
Links on this page:
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Subchronic toxicity studies with rodents are generally conducted for 90 days (3 months), but they may be
conducted for up to 12 months. Results of these studies (1) can help predict appropriate doses of the test
substance for future chronic toxicity studies, (2) can be used to determine NOELs for some toxicology
endpoints, and (3) allow future long-term toxicity studies in rodents and non-rodents to be designed with
special emphasis on identified target organs. Subchronic toxicity studies usually cannot determine the
carcinogenic potential of a test substance. Guidance specific to subchronic toxicity studies with non-rodents is
presented in chapter IV.C.4.b. Sponsors/submitters of petitions/notifications are encouraged to also become
familiar with the Guidance for Reporting Results of Toxicity Studies (Chapter IV.B.2.), Pathology
Considerations in Toxicity Studies (Chapter IV.B.3.), and Statistical Considerations in Toxicity Studies
(Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to the 1993 draft "Redbook II" version of this section have been made following
consultation with other authoritative guidelines and publications 1-8
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Redbook 2000: IV.C.4.a Subchronic Toxicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.4.a. Subchronic Toxicity Studies with Rodents
I. Good Laboratory Practice
Food
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Redbook 2000: IV.C.4.a Subchronic Toxicity Studies with Rodents
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Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"8
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines.
These guidelines are for studies with rodents (usually rats and mice); if other species are used, modifications
of these guidelines may be necessary. Both male and female test animals, that are healthy and have not been
subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies. The selection of the use of inbred, out-bred, or hybrid rodent strains for toxicity studies should be
based upon the scientific questions to be answered. Additionally, it is important that test animals come from
well-characterized and healthy colonies. Because recent information suggests survivability problems exist for
some strains of rats, test animals should be selected that are likely to achieve the recommended duration of
the study. FDA encourages petitioners and notifiers to consult with Agency scientists before toxicity testing is
begun if they have questions about the appropriateness of a particular species, strain, or substrain.
Testing should be performed on young animals, with dosing beginning as soon as possible after weaning,
following an acclimation period of at least 5 days, and for rodents no later than 6 to 8 weeks of age.
Equal numbers of males and females of each species and strain should be used for the study. In general, for
subchronic toxicity studies, experimental and control groups should have at least 20 rodents per sex per
group. Ten rodents/sex/group may be acceptable for subchronic rodent studies when the study is considered
to be range-finding in nature or when longer term studies are anticipated. These recommendations will help
ensure that the number of animals that survive until the end of the study will be sufficient to permit a
meaningful evaluation of toxicological effects.
If interim necropsies are planned, the number of animals per sex per group should be increased by the
number scheduled to be sacrificed before completion of the study; for rodents, at least 10 animals per sex per
group should be available for interim necropsy.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal must be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tatoo).
Animals should be housed one per cage (single-caged). This recommendation reflects three principal
concerns:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
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cannibalism.
In general, feed and water should be provided ad libitum to animals in toxicity studies, and the diets for these
studies should meet the nutritional requirements of the species 4-7 for normal growth and reproduction. Unless
special circumstances apply which justify otherwise, care should be taken to ensure that the diets of the
compound treated groups of animals are isocaloric (equivalent in caloric density) with and contain the same
levels of nutrients (e.g., fiber, micronutrients) as the diets of the control group. Unrecognized or inadequately
controlled dietary variables may result in nutritional imbalances or caloric deprivation that could confound
interpretation of the toxicity study results (e.g., lifespan, background rates of tumor incidences) and alter the
outcome and reproducibility of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test article doses than
expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed groups
to compensate for the differences in energy and nutrient content of the high dose diets. Such circumstances
make it especially important that feed consumption of these animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of litter-
mate weanling rats of the same sex and approximate size are selected and fed the control or the experimental
diet. Animals should be single-caged so that feed consumption can be determined daily, and the control
animal is then fed an amount of food equal to that which the paired experimental animal ate on the preceding
day. If the test substance is non-nutritive and composes a significant proportion of the diet, the pair-fed
control animals should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of
diet as the paired experimental animal. Additionally, the study should include a second group of control
animals fed ad libitum to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term and subchronic toxicity studies because of batch to batch variations in diet
composition (e.g., fiber, mineral, vitamins, isoflavones) in some of the commonly used laboratory animal
chows. The use of these semi-purified diets, however, may not be advisable in long-term and reproductive
studies due to inadequate historical data related to their influences on animal survival and toxicological
endpoints. For example, loss of necessary but unidentified micronutrients in the semipurified diet may
interfere with normal reproduction.
Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993 draft
"Redbook II"
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
H. Diet:
I. Assignment of Control and Compound Treated Animals:
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groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day; if this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. If the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
For example, under normal circumstances, mortality in the control group should not exceed 10%.
Adequate animal husbandry practices should result in considerably less than 10% of animals and tissues or
organs lost to a study because of autolysis. Autolysis in excess of this standard may be cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are similar in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
Animals should be exposed to the test substance 7 days per week for a minimum of 90 consecutive days (3
months). Any other regime must be justified.
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (for
example, in soft drinks or beer), or if administration in the diet is inappropriate for other reasons. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size; for rodents, the volume ordinarily should not exceed 1
ml/100 g body weight. If the gavage vehicle is oil (see Chapter IV.B.5.b. in the 1993 draft "Redbook II"),
then the volume should be no more than 0.4 ml/100 g of body weight, and the use of a low-fat diet
should be considered. If the test substance must be given in divided doses, all doses should be
administered within a 6 hour period. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished.
At least three dose levels of the test substance should be used per sex (one dose level per group); ideally, 4
or 5 dose levels of the test substance should be used. A concurrent control group should be included.
Information from acute (Chapter IV.C.2. in the 1993 draft "Redbook II") and short-term (Chapter IV.C.3.)
toxicity studies can help determine appropriate doses for subchronic studies.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in section "II Test Animals, H. Diet" above.)
C. Dose groups:
1. Selection of Treatment Doses:
2. Controls:
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Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 9
Routine cage-side observations should be made on all animals at least once or twice a day throughout the
study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10), conducted inside
and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions or other evidence of autonomic
activity (e.g., lacrimation, piloerection, pupil size, unusual respiratory pattern). Additionally, changes in gait,
posture and response to handling, as well as the presence of clonic or tonic seizures, stereotypes (e.g.,
excessive grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should
be recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Test animals should be weighed at least once a week. Feed consumption (or water consumption if the test
substance is administered in the drinking water) should be measured every week during the subchronic
toxicity study. Petitioners should also attempt to quantify spillage of feed by test animals, and to determine if
spillage is greater with test diets than with control diets. Appropriate discussions of feed spillage should be
included in the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
in the study.
2. 	Hematology: Blood samples should be obtained from a minimum of 10 rodents of each sex per group
at least three times during the study. Sampling of test animals should be conducted during the first two
weeks on study (receiving treatment), monthly or midway through treatment (day 45), and at
termination. The determination of the first sampling time point should be based on the expected time of
initial toxicological effects on the organ systems. Ideally, the same rodents should be sampled during the
study, and at termination. The collection of blood samples should occur at approximately the same time
on each sampling day. If animals are fasted prior to sampling, then blood collection should occur at the
conclusion of the fast and prior to feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Hematologic tests should be performed on individual samples and not
pooled.
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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1. 	The following determinations are recommended:
1. 	hematocrit
2. 	hemoglobin concentration
3. 	erythrocyte count
4. 	total and differential leukocyte counts
5. 	mean corpuscular hemoglobin
6. 	mean corpuscular volume
7. 	mean corpuscular hemoglobin concentration
8. 	and a measure of clotting potential (such as clotting time, prothrombin time, thromboplastin
time, or platelet count).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
3. 	Clinical Chemistry: 	Blood samples should be obtained from a minimum of 10 rodents of each sex per
group at least three times during the study. Sampling of test animals should be conducted during the
first two weeks on study (receiving treatment), monthly or midway through treatment (day 45), and at
termination. The determination of the first sampling time point should be based on the expected time of
initial toxicological effects on the organ systems. Ideally, the same rodents should be sampled during the
study, and at termination. The collection of blood samples should occur at approximately the same time
on each sampling day. If animals are fasted prior to sampling, then blood collection should occur at the
conclusion of the fast and prior to feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Clinical chemistry tests should be performed on individual samples and
not pooled.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, carbohydrate metabolism, and liver and kidney function. Specific determinations should
include:
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
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8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the test
compound may warrant the consideration of alternative tests. Appropriate justification for alternative
tests should be presented in study reports.
1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day10 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: Timed urine volume collection should be conducted during the last week of the study on at
least 10 animals of each sex in each group. The volume of urine collected, specific gravity, pH, glucose,
and protein should be determined as well as conducting a microscopic evaluation of urine for sediment
and presence of blood/blood cells 11 .
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
all subchronic toxicity studies with rodents (preferably rats). The neurotoxicity screen should be age
appropriate and would typically include: (1) specific histopathological examination of tissue samples
representative of major areas of the brain, spinal cord, and peripheral nervous system (see organs and
tissues listed below under VI.C. Preparation of Tissues for Microscopic Examination) and (2) a functional
battery of quantifiable observations and manipulative tests selected to detect signs of neurological,
behavioral, and physiological dysfunctions. This functional battery is also referred to as an expanded set
of clinical evaluations and is described more fully in section V.A. Observations of Test Animals in this
chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Subchronic toxicity study reports should include an assessment of the potential for the test substance to
adversely affect the structural or functional integrity of the nervous system. This assessment should
evaluate data from the neurotoxicity screen and other toxicity data from the study, as appropriate.
Based on this assessment, the petitioner should make an explicit statement about whether or not the
test substance presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed
appropriate. FDA recommends that additional neurotoxicity testing not be undertaken without first
consulting with the Agency.
6. 	Immunotoxicity: Results from tests that are included in the list of primary indicators for immune
toxicity (see Chapter V.C. of the 1993 draft "Redbook II") should also be evaluated as part of an
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immunotoxicity screen. Reports of subchronic toxicity studies should include an assessment of the
potential for the test substance to adversely affect the immune system. This assessment should evaluate
data from the list of primary indicators included in the immunotoxicity screen and other toxicity data
from the study, as appropriate. Based on this assessment, the petitioner/notifier should make an explicit
statement about whether or not the test substance presents a potential immunotoxic hazard which
requires further immunotoxicity testing. Additional immunotoxicity tests are discussed in Chapter V. C.
of the 1993 draft "Redbook II", but should not be undertaken without first consulting with the Agency.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	Harderian gland (if present)
15. 	heart
16. 	ileum
17. 	jejunum
18. 	kidneys
19. 	liver
20. 	lung (with main-stem bronchi)
21. 	lymph nodes (1 related to route of administration and 1 from a distant location)
22. 	mammary glands
23. 	nasal turbinates
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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24. 	ovaries and fallopian tubes
25. 	pancreas
26. 	pituitary
27. 	prostate
28. 	rectum
29. 	salivary gland
30. 	sciatic nerve
31. 	seminal vesicle (if present)
32. 	skeletal muscle
33. 	skin
34. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
35. 	spleen
36. 	stomach
37. 	testes
38. 	thymus (or thymic region)
39. 	thyroid/parathyroid
40. 	trachea
41. 	urinary bladder
42. 	vagina
43. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V. C. of the 1993 draft "Redbook II") for all animals.
1. 	EPA Health Effects Test Guidelines OPPTS 870.3100, 90-Day Oral Toxicity in Rodents, August 1998
2. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 90-day Oral Toxicity Study in Rodents,
408, September 1998
3. 	Kurt Weingand et al., 1996. "Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety
Studies", Fundamental and Applied Toxicology, 29, pp 198-201.
4. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995
5. 	Nutrient Requirement of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
6. 	Nutrient Requirements of Swine, 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
7. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
8. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
9. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
10. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
11. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor&Francis, Philadelphia, PA, pp. 520-533
Links on this page:
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Subchronic toxicity studies with non-rodents (usually dogs) are generally conducted for 90 days (3 months),
but they may be conducted for up to 12 months. Results of these studies (1) can help predict appropriate
doses of the test substance for future chronic toxicity studies, (2) can be used to determine NOELs for some
toxicology endpoints, and (3) allow future long-term toxicity studies in rodents and non-rodents to be
designed with special emphasis on identified target organs. Subchronic toxicity studies usually cannot
determine the carcinogenic potential of a test substance. Guidance specific to subchronic toxicity studies with
rodents is presented in chapter IV.C.4b. Sponsors/submitters of petitions/notifications are encouraged to also
become familiar with the Guidance for Reporting Results of Toxicity Studies (Chapter IV.B.2.), Pathology
Considerations in Toxicity Studies (Chapter IV.B.3.), and Statistical Considerations in Toxicity Studies
(Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to the 1993 draft "Redbook II" version of this section have been made following
consultation with other authoritative guidelines and publications 1-8
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Redbook 2000: IV.C.4.b Subchronic Toxicity Studies with Non-Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.4.b. Subchronic Toxicity Studies with Non-Rodents
I. Good Laboratory Practice
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.4.b Subchronic Toxicity Studies with Non-Rodents
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Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"8
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines.
These guidelines are for studies with non-rodents (usually dogs); if other species are used, modifications of
these guidelines may be necessary. Both male and female test animals, that are healthy and have not been
subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting species and strains for toxicity studies. Test animals
should be selected that are likely to survive the recommended duration of the study. It is important that test
animals come from well-characterized and healthy colonies. FDA encourages petitioners and notifiers to
consult with Agency scientists before toxicity testing is begun if they have questions about the
appropriateness of a particular species or strain.
Testing should be performed on young animals, with dosing beginning as soon as possible after weaning, and
following an acclimation period of at least 5 days. Testing should begin when dogs are no older than 4 to 6
months of age.
Equal numbers of males and females of each species and strain should be used for the study. In general, for
subchronic toxicity studies, experimental and control groups should have at least 4 dogs per sex per group.
These recommendations will help ensure that the number of animals that survive until the end of the study
will be sufficient to permit a meaningful evaluation of toxicological effects.
If interim necropsies are planned, the number of animals per sex per group should be increased by the
number scheduled to be sacrificed before completion of the study.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain, sex, age, and weight. Each animal
must be assigned a unique identification number (e.g., ear tag, implanted identification chip, tatoo).
Animals should be housed one per cage or run (single-caged). This recommendation reflects three principal
concerns:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
Diets for subchronic studies should meet the nutritional requirements of the species 4-7 for normal growth and
reproduction. In general, water should be provided ad libitum . Unless special circumstances apply which
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
H. Diet:
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justify otherwise, care should be taken to ensure that the diets of the compound treated groups of animals are
isocaloric (equivalent in caloric density) with and contain the same levels of nutrients (e.g., fiber,
micronutrients) as the diets of the control group. Unrecognized or inadequately controlled dietary variables
may result in nutritional imbalances or caloric deprivation that could confound interpretation of the toxicity
study results (e.g., lifespan, background rates of tumor incidences) and alter the outcome and reproducibility
of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. It is important that feed consumption of animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of animals
of the same sex, age, and approximate size are selected and fed the control or the experimental diet. Animals
should be single-caged so that feed consumption can be determined daily, and the control animal is then fed
an amount of food equal to that which the paired experimental animal ate on the preceding day. If the test
substance is non-nutritive and composes a significant proportion of the diet, the pair-fed control animals
should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of diet as the
paired experimental animal. Additionally, the study should include a second group of control animals fed the
normal ration amount to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term and subchronic toxicity studies because of batch to batch variations in diet
composition (e.g., fiber, mineral, vitamins, isoflavones) in some of the commonly used laboratory animal
chows. The use of these semi-purified diets, however, may not be advisable in long-term and reproductive
studies due to inadequate historical data related to their influences on animal survival and toxicological
endpoints. For example, loss of necessary but unidentified micronutrients in the semipurified diet may
interfere with normal reproduction.
FDA recommends reviewing the diet section in IV.C.4.a. when non-rodents (e.g., rabbits)are to be fed ad
libitum. Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993
draft "Redbook II".
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day; if this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. If the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
I. Assignment of Control and Compound Treated Animals:
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Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
For example, under normal circumstances, mortality in the control group should not exceed 10%.
Adequate animal husbandry practices should result in considerably less than 10% of animals and tissues or
organs lost to a study because of autolysis. Autolysis in excess of this standard may be cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are similar in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
Animals should be exposed to the test substance 7 days per week for a minimum of 90 consecutive days (3
months). Any other regime must be justified.
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (for
example, in soft drinks or beer), or if administration in the diet is inappropriate for other reasons. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished.
At least three dose levels of the test substance should be used per sex (one dose level per group); ideally, 4
or 5 dose levels of the test substance should be used. A concurrent control group should be included.
Information from acute (Chapter IV.C.2. in the 1993 draft "Redbook II") and short-term (Chapter IV.C.3.)
toxicity studies can help determine appropriate doses for subchronic studies.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in section "II Test Animals, H. Diet" above.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 9
Routine cage-side observations should be made on all animals at least once or twice a day throughout the
C. Dose groups:
1. Selection of Treatment Doses:
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
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study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10), conducted inside
and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions or other evidence of autonomic
activity (e.g., lacrimation, piloerection, pupil size, unusual respiratory pattern). Additionally, changes in gait,
posture and response to handling, as well as the presence of clonic or tonic seizures, stereotypes (e.g.,
excessive grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should
be recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Test animals should be weighed at least once a week. Feed consumption (or water consumption if the test
substance is administered in the drinking water) should be measured every week during the subchronic
toxicity study. Petitioners should also attempt to quantify spillage of feed by test animals, and to determine if
spillage is greater with test diets than with control diets. Appropriate discussions of feed spillage should be
included in the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: 	This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
in the study.
2. 	Hematology: 	Blood samples should be obtained from all animals of all groups at the following times:
prior to initiation of treatment, during the first two weeks on study (receiving treatment), monthly or
midway through treatment (day 45), and at termination. The determination of the second sampling time
point should be based on the expected time of initial toxicological effects on the organ systems. The
collection of blood samples should occur at approximately the same time on each sampling day. If
animals are fasted prior to sampling, then blood collection should occur at the conclusion of the fast and
prior to feeding. Fasting duration should be appropriate for the species and the analytical tests to be
performed. Hematologic tests should be performed on all samples individually, and not pooled.
1. 	The following determinations are recommended:
1. 	hematocrit
2. 	hemoglobin concentration
3. 	erythrocyte count
4. 	total and differential leukocyte counts
5. 	mean corpuscular hemoglobin
6. 	mean corpuscular volume
7. 	mean corpuscular hemoglobin concentration
8. 	and a measure of clotting potential (such as clotting time, prothrombin time, thromboplastin
time, or platelet count).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
3. 	Clinical Chemistry: 	Blood samples should be obtained from all animals of all groups at the following
times: prior to initiation of treatment, during the first two weeks on study (receiving treatment), monthly
or midway through treatment (day 45), and at termination. The determination of the second sampling
time point should be based on the expected time of initial toxicological effects on the organ systems. The
collection of blood samples should occur at approximately the same time on each sampling day. If
animals are fasted prior to sampling, then blood collection should occur at the conclusion of the fast and
prior to feeding. Fasting duration should be appropriate for the species and the analytical tests to be
performed. Clinical chemistry tests should be performed on all samples individually, and not pooled.
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
1. 	However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the
test compound may warrant the consideration of alternative tests. Appropriate justification for
alternative tests should be presented in study reports.
1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
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4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day10 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: Timed urine volume collection should be conducted on all animals in the study, pretest, at
30 and 60 days, and during the last week of the study. The volume of urine collected, specific gravity,
pH, glucose, and protein should be determined as well as conducting a microscopic evaluation of urine
for sediment and presence of blood/blood cells 11 .
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
all subchronic toxicity studies with non-rodents (preferably dogs or miniature swine). The neurotoxicity
screen should be age appropriate and would typically include: (1) specific histopathological examination
of tissue samples representative of major areas of the brain, spinal cord, and peripheral nervous system
(see organs and tissues listed below under VI.C. Preparation of Tissues for Microscopic Examination) and
(2) a functional battery of quantifiable observations and manipulative tests selected to detect signs of
neurological, behavioral, and physiological dysfunctions. This functional battery is also referred to as an
expanded set of clinical evaluations and is described more fully in section V.A. Observations of Test
Animals in this chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Subchronic toxicity study reports should include an assessment of the potential for the test substance to
adversely affect the structural or functional integrity of the nervous system. This assessment should
evaluate data from the neurotoxicity screen and other toxicity data from the study, as appropriate.
Based on this assessment, the petitioner should make an explicit statement about whether or not the
test substance presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed
appropriate. FDA recommends that additional neurotoxicity testing not be undertaken without first
consulting with the Agency.
6. 	Immunotoxicity: Results from tests that are included in the list of primary indicators for immune
toxicity (see Chapter V.C. of the 1993 draft "Redbook II" ) should also be evaluated as part of an
immunotoxicity screen. Reports of subchronic toxicity studies should include an assessment of the
potential for the test substance to adversely affect the immune system. This assessment should evaluate
data from the list of primary indicators included in the immunotoxicity screen and other toxicity data
from the study, as appropriate. Based on this assessment, the petitioner/notifier should make an explicit
statement about whether or not the test substance presents a potential immunotoxic hazard which
requires further immunotoxicity testing. Additional immunotoxicity tests are discussed in Chapter V. C.
of the 1993 draft "Redbook II", but should not be undertaken without first consulting with the Agency.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
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Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	Harderian gland (if present)
15. 	heart
16. 	ileum
17. 	jejunum
18. 	kidneys
19. 	liver
20. 	lung (with main-stem bronchi)
21. 	lymph nodes (1 related to route of administration and 1 from a distant location)
22. 	mammary glands
23. 	nasal turbinates
24. 	ovaries and fallopian tubes
25. 	pancreas
26. 	pituitary
27. 	prostate
28. 	rectum
29. 	salivary gland
30. 	sciatic nerve
31. 	seminal vesicle (if present)
32. 	skeletal muscle
33. 	skin
34. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
35. 	spleen
36. 	stomach
37. 	testes
38. 	thymus (or thymic region)
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
39. 	thyroid/parathyroid
40. 	trachea
41. 	urinary bladder
42. 	vagina
43. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V. C. of the 1993 draft "Redbook II") for all animals.
1. 	EPA Health Effects Test Guidelines OPPTS 870.3150, 90-Day Oral Toxicity in Non-Rodents, August 1998
2. 	OECD Guideline For The Testing Of Chemicals , Repeated Dose 90-day Oral Toxicity Study in Non-
Rodents, 409, September 1998
3. 	Kurt Weingand et al., 1996. "Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety
Studies", Fundamental and Applied Toxicology, 29, pp 198-201.
4. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995.
5. 	Nutrient Requirements of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
6. 	Nutrient Requirements of Swine: 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
7. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
8. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
9. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
10. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
11. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor&Francis, Philadelphia, PA, pp. 520-533
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
Links on this page:
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
The FDA has made scientifically justified changes to 1993 "draft" Redbook Chapter IV.C.7., Combined Chronic
Toxicity/Carcinogenicity Studies with Rodents, and developed Chapter IV.C.5.a., Chronic Toxicity Studies with
Rodents, after consulting other authoritative guidelines[6] [7] [12] and publications [1] (see also relevant
sections below). This section of Redbook 2000 supersedes the 1993 "draft" Redbook Chapter IV.C.7.
The FDA acknowledges that it is complicated and difficult to conduct a combined study due to difficulty in
setting and administering appropriate dose levels for both types of studies concurrently. In addition, the
general objectives of these two types of studies are different. However, when pre-chronic studies provide
reasonable estimates of toxicity to predict the information (e.g., treatment doses) to be used in a single
bioassay, a chronic toxicity study may be combined with a carcinogenicity study and reveal information about
an ingredient’s potential to be a carcinogen as well as the maximum dose that produces no adverse effects.
On a case-by-case, an in-utero exposure phase may also be added to a chronic toxicity study (or combined
chronic toxicity/carcinogenicity study) to determine early developmental effects that may increase the
incidence of chronic disease outcomes (and/or cancers). Sponsors/submitters of petitions/notifications are
encouraged to become familiar with the Carcinogenicity Studies with Rodents (Chapter IV.C.6. 2 ) and In-utero
Exposure Phase for Addition to Carcinogenicity Studies or Chronic Toxicity Studies with Rodents (Chapter
IV.C.8. 3 ) during the development of a combined study design. The petitioner/notifier should also consult with
the FDA before conducting a combined study.
Chronic toxicity studies with rodents should be conducted for a minimum of 12 months (one-year). Results of
Redbook 2000: IV.C.5.a Chronic Toxicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.5.a. Chronic Toxicity Studies with Rodents
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Redbook 2000: IV.C.5.a Chronic Toxicity Studies with Rodents
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these tests can be used, 1) to characterize the toxicity of a food ingredient following prolonged and repeated
exposure, and 2) to determine toxicological dose-response relationships needed to establish the maximum
dose that produces no adverse effects (i.e., NOEL or NOAEL). The following guidance is written primarily for
rats or mice, if other non-rodents are used, modifications to the guidance may be necessary.
Sponsors/submitters of petitions/notifications are encouraged to also become familiar with the Guidelines for
Reporting Results of Toxicity Studies (Chapter IV.B.2. 4
), Pathology Considerations in Toxicity Studies
(Chapter IV.B.3. 5 ), Statistical Considerations in Toxicity Studies (Chapter IV.B.4. 6 ), during the development
of study design.
Nonclinical laboratory studies discussed in this chapter should be conducted according to U.S. FDA good
laboratory practice (GLP) regulations, issued under Part 58 of Title 21 7 of the Code of Federal Regulations.
This document may be obtained from the Superintendent of Documents, U.S. Government Printing Office,
Washington, D.C., 20402, (toll free 866-512-1800 or DC area 202-512-1800). Studies performed under other
international/national guidelines may be considered equivalent to those conducted under U.S. FDA GLP
regulations. Specific area(s) of non-compliance with FDA GLP regulations should be discussed and justified.
Recommendations about the care, maintenance, and housing of animals contained in the National Research
Council, Guide for the Care and Use of Laboratory Animals[13] should be followed unless they conflict with
specific recommendations in this chapter.
Guidance contained within this chapter is for studies with mice and rats; if other rodent species are used,
modifications may be necessary. Both male and female test animals, which are healthy and have not been
subjected to previous experimental procedures, should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies. The selection of inbred, out-bred, or hybrid rodent strains for toxicity tests should be based upon the
scientific questions to be answered. Additionally, it is important that test animals come from well-
characterized and healthy colonies. The petitioners/notifiers should consult with the Agency scientists before
toxicity testing has begun if they have questions about the appropriateness of a particular species, strain, or
substrain.
Dosing of rodents should begin after weaning, and following a suitable acclimation period of at least 5 days,
and before they are approximately 6-8 weeks old.
Both experimental and control groups should have at least 20 rodents per sex per group. If interim
necropsies are planned, the total number of rodents of each sex per group should be increased by the number
scheduled to be sacrificed before completion of the study. A minimum of 10 rodents per sex per group should
be available for each interim necropsy.
Generally, it is not possible to treat animals for infection during the course of a study without the possibility of
interaction between the therapeutic agent used for treatment and the test substance. This interaction may
seriously confound or complicate the interpretation of study results. However, if problems with infection do
occur, the sponsor for the study should use their best judgment in proceeding with the study and inform the
Agency of their decision. In addition, the FDA requests that they provide a full and detailed description of the
justification for study continuation and possible implications of the infection, and if applicable, the justification
and possible implications for treatment of the infection.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal should be assigned a unique identification number (e.g., ear tag, implanted identification
I. Good Laboratory Practice
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species and Strains:
C. Age (start of dosing):
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
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chip, tattoo).
Animals should be housed one per cage. This recommendation reflects three points of consideration:
z The amount of feed consumed by each animal in the study cannot be determined with sufficient
accuracy when more than one animal is housed in each cage. This information is necessary in
the determination of feed efficiency (relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses in determining whether decreases in body
weight gain are due to decreased palatability or test substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost
due to cannibalism.
In general, feed and water should be provided ad libitum, and the diets should meet the nutritional
requirements of the species [14] for normal growth and longevity. Unless special circumstances apply which
justify otherwise, care should be taken to ensure that the diets of the test substance treated groups of
animals contain the same levels of calories and nutrients (e.g., fiber, micronutrients) as the diets of the
control group. Inadequately controlled dietary variables may result in nutritional imbalances or caloric
deprivation that could confound interpretation of the toxicity study results (e.g., lifespan, background rates of
tumor incidences) and alter the outcome and reproducibility of the studies. However, the Agency is also
aware of some beneficial effects on the survivability of certain animal species that have been on calorie-
restricted, [4] [5] or low-protein diets. [2] [9] The Agency may accept such study results if the sponsor provides
sufficient historical control data on the diet, and the study is well-conducted.
The following issues are important to consider when establishing diets for animals in chronic toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test substance doses
than expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed
groups to compensate for the differences in energy and nutrient content of the high dose diets. Such
circumstances make it especially important that feed consumption of these animals be as accurately and
closely monitored as possible in order to determine whether changes observed could be due to overt toxicity
of the test substance or to a dietary imbalance. To further aid in this assessment, two control groups can be
used; one group would be fed the undiluted control diet and a second group would be fed the control diet
supplemented with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the
test substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, other feeding regimens or experimental designs may be necessary. Consultation
with the FDA is recommended when alternatives are being considered.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
Other related issues (e.g., advantages and disadvantages of using natural ingredient versus purified diets) are
discussed in the National Research Council publication on nutrient requirements of laboratory animals.[14]
G. Caging:
H. Diet:
I. Assignment of Control and Compound Treated Animals:
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Animals should be assigned to control and compound treated groups in a stratified random manner. This will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups. In general, mean body weights and/or body weight ranges are used as a basis of randomization. If
other characteristics are used as the basis for randomization, they should be described and justified.
Animals in all groups should be placed on study on the same day. If this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. When the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be a cause to repeat the study.
Adequate animal husbandry practices should result in considerably less than 10 % loss of animals and tissues
or organs in a study because of autolysis. Autolysis in excess of this standard may be a cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated
at a temperature that is low enough to prevent autolysis (i.e., between 4°C and 8°C), but not so low as to
cause cell damage. If histopathological examination is to be conducted, tissue specimens should be taken
from the animals and placed in appropriate fixatives when the necropsy is performed.
The test substance used in chronic toxicity studies should be the same substance that the petitioner/notifier
intends to market or, when appropriate, the test substance may be a constituent chemical or an impurity. A
single lot of test substance should be used throughout the study. When this is not possible, lots that are as
similar as possible in purity and composition should be used. It is the responsibility of the petitioner/notifier
to notify the animal test facility of the purity of the test substance, as well as the identity and concentration of
any impurities that might be present.
The identity of the test substance (e.g., either a single component or a mixture of components) should be
known. The petitioners/notifiers are encouraged to consult with the Agency regarding the method(s) of
determination of the test substance, and should provide all relevant Chemical Abstract Service (CAS) Registry
numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test samples should be stored under conditions that maintain their stability and purity until the studies
are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
The test animal should be exposed to the test substance 7 days per week for at least 12 months (one year).
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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The route of administration of the test substance should approximate that of normal human exposure, and if
possible, the oral route should be used. A justification should be provided when using other routes. The same
method of administration should be used for all test animals throughout the study. The test substance should
be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid
foods or a combination of solid and liquid foods. If the test substance is added to the diet,
animals should not be able to selectively consume either basal diet or test substance in the diet
on the basis of color, smell, or particle size. If the test substance is mixed with ground feed and
pelleted, nothing in the pelleting process should affect the test substance (for example, heat-
labile substances may be destroyed during pellet production by a steam process). When the test
substance is administered in the diet, dietary levels should be expressed as mg of the test
substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form by
humans (for example, in soft drinks or beer), or if administration in the diet of rodents is
inappropriate. The amount of test substance administered in drinking water should be expressed
as mg of test substance per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are
unsatisfactory or if human exposure is expected to be through daily ingestion of a single, large
bolus dose instead of continual ingestion of small doses. If the test substance is administered by
gavage, it should be given at approximately the same time each day. The maximum volume of
solution that can be given by gavage in one dose depends on the test animal's size; for rodents,
the volume ordinarily should not exceed 1 ml/100 g body weight. If the gavage vehicle is oil,
then the volume should be no more than 0.4 ml/100 g of body weight, and the use of a low-fat
diet should be considered. It is best to adjust the volume every 1-3 days based on the animal’s
body weight response. If the test substance should be given in divided doses, all doses should
be administered within a 6 hour period. Doses of test substance administered by gavage should
be expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier
should provide information that can allow the Agency to conclude that administration of the test
substance by encapsulation or gavage is equivalent in toxicologically important respects to
administration in the diet or drinking water. Alternatively, metabolic information on both modes
of administration should be provided so that appropriate interpretation of data can be
accomplished.
Dose selection for chronic toxicity studies should be based on results from subchronic studies and other
related information. Appropriate dose selection should enable one to predict the maximum dose that
produces no adverse effects, also known as the NOEL or NOAEL. A rationale should be provided for the dose
selection. Administration of the test substance to all dose groups should be done concurrently (see section
II.I: Assignment of Control and Compound Treated Animals).
A concurrent control group of test animals fed the basal diet is necessary. A carrier or vehicle for the test
substance should be given to control animals at a volume equal to the maximum volume of carrier or vehicle
given to any group of treated animals. Sufficient toxicological information should be available on the carrier
or vehicle to ensure that its use will not compromise the results of the study. If there is insufficient
information about the toxic properties of the carrier or vehicle used to administer the test substance, an
additional control group that is not exposed to the carrier or vehicle should be included. In all other respects,
animals in the control group should be treated the same as animals in dosed groups. (See also section II.H:
Diet.)
We recommend that a minimum of three dose levels of the test substance should be used in chronic toxicity
studies. The following is a general consideration in selecting the treatment dose levels: 1) the high dose
should be sufficiently high to induce toxic responses in test animals, and should not cause fatalities high
enough to prevent meaningful evaluation of the data from the study; 2) the low dose should not induce
biologically significant toxic responses in test animals; and 3) the intermediate dose should be sufficiently high
C. Dose groups:
1. Controls:
2. Selection of Treatment Doses:
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to elicit minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body
weight gains).
We do not recommend that petitioner/notifiers use information unrelated to the toxicity of the test substance
as a basis for dose selection of chronic toxicity studies. For example, the highest dose in a chronic toxicity
study should not be selected so as to provide a pre-determined margin of safety over the maximum expected
human exposure to the test substance, assuming that the results of testing at that dose will be negative.
High Dose:
The high dose in a chronic toxicity study should produce toxicity so that a toxicological profile of the test
substance can be obtained. When no toxicity is observed in other studies, however, the high dose could be
subject to some preset limits such as the highest percent of the test substance in the diet that could be fed
without compromising nutritional balance with other nutrients (e.g., about 5%, see also ‘section II.H: Diet’ for
other important dietary issues).
In general, the high dose tested is estimated following a careful analysis of data from appropriate subchronic
toxicity tests. As the scientific community's experience with toxicity testing has accumulated, the need to
consider a broad range of biological information when selecting the high dose has become increasingly clear.
For example, data from a subchronic (90-day) study concerning changes in body and organ weight and
clinically significant alterations in neurological, hematological, urinary and clinical chemistry measurements, in
combination with more definitive exposure-related toxic, gross or histopathologic endpoints, can be used to
estimate the high dose in a chronic toxicity study.
Although the high dose in a chronic toxicity study should be selected to achieve toxic responses in test
animals, and should not cause fatalities high enough to prevent meaningful evaluation of the data from the
study, the Agency recognizes that this goal may not always be met. In situations such as these, when it is
unclear what dose of the test substance is the high dose, the petitioner/notifier should consult with the Agency
to determine an appropriate high dose for the chronic toxicity study.
Low Dose:
The low dose level should not interfere with the normal growth, development, and lifespan of test animals, nor
should it produce any other biologically significant signs of toxicity (e.g., NOEL or NOAEL).
Intermediate Dose:
The intermediate dose should produce minimal signs of toxicity. The exact dose selected as the intermediate
dose may depend on the pharmacokinetic properties of the test substance.
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are consistent with the intention of the Good
Laboratory Practice principles. [11] The FDA has endorsed the use of the Standard for Exchange of Nonclinical
Data (SEND) format for electronic transmission of animal study data. You are encouraged to contact the
Agency for more information on this electronic protocol.
Routine cage-side observations should be made on all animals inside the cage once or twice a day throughout
the study for signs of departure from normal activity, morbidity and mortality. The usual interval between
multiple periods of observations should be at least 6 hours. Individual records should be maintained for each
animal and, as possible, the onset and progression of any effects should be recorded, preferably using a
scoring system. If grossly visible or palpable tumors develop, the following parameters should be recorded;
time of onset, location, dimensions, appearance and progression.
An expanded set of clinical evaluations performed on animals inside and outside of the cage, should be carried
out to enable detection not only of general signs of departure from normal activity, morbidity and mortality
but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other signs of nervous
system toxicity. Specific information about the systematic clinical tests/observations is contained in Chapter
IV.C.10 8 . This expanded set of clinical examinations, conducted on animals inside and outside the cage,
should be age appropriate and performed on all animals at least once prior to initiation of treatment, and
periodically during treatment. Signs noted should include, but not be limited to, changes in skin, fur, eyes,
mucous membranes, occurrence of secretions and excretions or other evidence of autonomic activity (e.g.,
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
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lacrimation, piloerection, pupil size, unusual respiratory pattern). Additionally, changes in gait, posture and
response to handling, as well as the presence of clonic or tonic seizures, stereotypic (e.g., excessive
grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Accurate individual body weight, feed, and water consumption measurements are critical in the objective
evaluation of the effect of a test substance on experimental animals, since changes in these variables are
often the first signs of toxicity. Complete records for these parameters are essential in assessing the time-
related occurrence of toxicity-induced changes including tumor formation. A discussion of some of the
variables that affect feed consumption and weight gain/loss can be found under sections II.H: Diet and IV.B:
Route of Administration.
Body weights for all test animals should be recorded weekly for the first 13 weeks, and monthly thereafter for
the duration of the study. Feed consumption (or water consumption if the test substance is administered in
the drinking water) should be measured at the same interval as body weights; petitioners/notifiers should also
attempt to quantify spillage of feed by test animals. When it is suspected that test substance administration
may be affected by any of the following conditions; 1) feed palatability issues, 2) marked changes in body
weight, or 3) increased numbers of animal deaths, the petitioners/notifiers should measure weights and feed
(water) consumption more frequently after the initial 13 week period (e.g., every two weeks).
Petitioners/notifiers should also use this accumulated information to calculate intake of the test substance as
mg/kg body weight/day.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
This examination should be performed by a qualified individual on all animals before the study begins and on
control and high-dose animals at the end of the study. If the results of examinations at termination indicate
that changes in the eyes may be associated with administration of the test substance, ophthalmological
examinations should be performed on all animals in the study.
Hematological tests should be performed on all animals during the first 2 weeks of study, at 3, 6 and 12
months during the study. The time of the first sampling may be based on test results from short-term
studies. If data trends or significant parameter changes (biological or statistical) are observed that are of
concern at the 12-month measurement and the study lasts longer than one-year, additional hematological
testing should be conducted at the end of the study.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be analyzed
individually, and not pooled. If, due to the large number of animals, it becomes necessary to draw blood
samples on more than one consecutive day at each sampling point, the samples should be obtained at
approximately the same time each day.
The following determinations are recommended: hematocrit, hemoglobin concentration, erythrocyte count,
total and differential leukocyte counts, mean corpuscular hemoglobin, mean corpuscular volume, mean
corpuscular hemoglobin concentration, platelet count, and a measure of clotting potential (e.g., clotting time,
prothrombin time, activated partial thromboplastin time).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures should
be employed so that evaluations of reticulocyte counts and bone marrow cytology may be performed if
warranted. Reticulocyte counts should be obtained for each animal using automated reticulocyte counting
capabilities, or from air-dried blood smears. Bone marrow slides for cytological evaluation should be prepared
from each animal. These slides only need to be microscopically examined when effects on the hematopoietic
system are noted.
Clinical chemistry tests should be performed on all animals during the first 2 weeks of study, and at 3, 6 and
12 months during the study. The time of the first sampling may be based on test results from short-term
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
1. Ophthalmological Examination:
2. Hematology:
3. Clinical Chemistry:
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studies. If data trends or significant parameter changes (biological or statistical) are observed that are of
concern at the 12-month measurement and the study lasts longer than one-year, additional clinical chemistry
testing should be conducted at the end of the study.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be drawn at
the end of the fasting time and before feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Blood samples should be analyzed individually, and not pooled. If animals
are sampled on more than one day during a study, blood should he drawn at approximately the same time
each sampling day.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, nutrients metabolism, and liver and kidney function. Specific determinations should include:
Hepatocellular evaluation (at least 3 of the following 5)
z Alanine aminotransferase (SGPT, ALT)
z Aspartate aminotransferase (SGOT, AST)
z Sorbitol dehydrogenase
z Glutamate dehydrogenase
z Total bile acids
Hepatobiliary evaluation (at least 3 of the following 5)
z Alkaline phosphatase
z Bilirubin (total)
z Gamma-glutamyl transpeptidase (GG transferase)
z 5' nucleotidase
z Total bile acids
Other markers of cell changes or cellular function
z Albumin
z Calcium
z Chloride
z Cholesterol (total)
z Cholinesterase
z Creatinine
z Globulin (calculated)
z Glucose
z Phosphorous
z Potassium
z Protein (total)
z Sodium
z Triglycerides
z Urea nitrogen
z The Agency understands that the specific nature of the test substance may warrant the
consideration of alternative tests. Appropriate justification for alternative tests should be
presented in study reports.
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In spite of standard operating procedures and equipment calibration, it is not unusual to observe considerable
variation in the results of clinical chemistry analyses from day to day. [3] Ideally, clinical chemistry analyses
for all dose groups should be completed during one day. If this is not possible, analyses should be conducted
in such a way as to minimize potential variability.
The determination of volume of urine collected, urine specific gravity, pH, glucose, and protein, as well as
microscopic analysis of urine for sediment and presence of blood and/or blood cells, are recommended[8]
before dosing, and at 3, 6 and 12 months during the study. If data trends or significant parameter changes
(biological or statistical) are observed that are of concern at the 12-month measurement and the study lasts
longer than one-year, additional urinalyses testing should be conducted at the end of the study. These tests
should be performed on all animals.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination.
Organs that should be weighed at minimum include the adrenals, brain, epididymides, heart, kidneys, liver,
spleen, testes, prostate, thyroid/parathyroid, thymus if present, ovaries and uterus. Before being weighed,
organs should be carefully dissected and trimmed to remove fat and other contiguous tissue. Organs should
be weighed immediately after dissection to minimize the effects of drying on organ weight.
Generally, the following tissues should be fixed in 10 % buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
z Adrenals
z Aorta
z Bone (femur)
z Bone marrow (sternum)
z Brain (at least 3 different levels)
z Cecum
z Colon
z Corpus and cervix uteri
z Duodenum
z Epididymides
z Esophagus
z Eyes
z Gall bladder (if present)
z Harderian gland
z Heart
z Ileum
z Jejunum
4. Urinalyses:
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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z Kidneys
z Liver
z Lung (with main-stem bronchi)
z Lymph nodes (1 related to route of administration and 1 from a distant location)
z Mammary glands
z Nasal turbinates
z Ovaries and fallopian tubes
z Pancreas
z Pituitary
z Prostate
z Rectum
z Salivary gland
z Sciatic nerve
z Seminal vesicle (if present)
z Skeletal muscle
z Skin
z Spinal cord (3 locations: cervical, mid-thoracic, and lumbar)
z Spleen
z Stomach
z Testes
z Thymus (if present)
z Thyroid/parathyroid
z Trachea
z Urinary bladder
z Vagina
z Zymbal's gland
z All tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then those specific
tissues in the next lower dose level tested should be examined. Successive examination of the next lower
dose level continues until no effects are noted. In addition, all tissues from animals that died prematurely or
were sacrificed during the study should be examined microscopically. If there are questions related to the
review and interpretation of pathological lesions and statistical results, additional discussion may be found in
Chapters IV.B.3 9
. and IV.B.4 10 . of the Redbook 2000.
Histological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V.D. of the 1993 draft Redbook II). A recent publication provides further
discussion on this subject. [10]
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078388.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078394.htm
4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
1 Chhabra, R.S., J.E. Huff, B.S. Schwetz, and J. Selkirk, An Overview of Prechronic and Chronic
Toxicity/Carcinogenicity Experimental Study Designs and Criteria Used by the National Toxicology Program,
Environmental Health Perspectives, 86:313-321, 1990.
2 Clinton S.K., A.L. Mulloy, S.P. Li, H.J. Mangian and W.J. Visek, Dietary Fat and Protein Intake Differ in
Modulation of Prostate Tumor Growth, Prolactin Secretion and Metabolism, and Prostate Gland Prolactin
Binding Capacity in Rats, The Journal of Nutrition, 127:225-237, 1997.
3 Gaylor D.W., R.L. Suber, G.L. Wolff and J.A Crowell, Statistical Variation of Selected Clinical Pathological
and Biochemical Measurements in Rodents, Proceedings of the Society for Experimental Biology and Medicine,
185:361-367, 1987.
4 Keenan K.P., C.M. Hoe, L Mixson, C.L. McCoy, J.B. Coleman, B.A. Mattson, G.A. Ballam, L.A. Gumprecht,
and K.A. Soper, Diabesity: A Polygenic Model of Dietary-Induced Obesity from ad libitum Overfeeding of
Sprague-Dawley Rats and its Modulation by Moderate and Marked Dietary Restriction, Toxicologic Pathology,
33:650-674, 2005.
5 Keenan K.P., J.B. Coleman, C.L. McCoy, C.M. Hoe, K.A. Soper and P. Laroque, Chronic Nephropathy in ad
libitum Overfed Sprague-Dawley Rats and its Early Attenuation by Increasing Degrees of Dietary (Caloric)
Restriction to Control Growth, Toxicologic Pathology, 26(6):788-798, 2000.
6 Organization for Economic Cooperation and Development (OECD), Environment, Health and Safety
Publications, Series on Testing and Assessment No. 35 and Series on Pesticides No. 14, Guidance Notes for
Analysis and Evaluation of Chronic Toxicity and Carcinogenicity Studies, Paris, 2002.
7 OECD, Guideline for Testing of Chemicals, No. 452, Chronic Toxicity Studies, Adopted in 1981.
8 Ragan H.A. and R.E. Weller, Markers of Renal Function and Injury, In: The Clinical Chemistry of Laboratory
Animals, Second Edition, Taylor & Francis, Philadelphia, PA, pp. 520-533, 1999.
9 Rao G.N. and P.W. Crockett, Effect of Diet and Housing on Growth, Body Weight, Survival and Tumor
Incidences of B6C3F1 Mice in Chronic Studies, Toxicologic Pathology, 31(2):243-250, 2003.
10 Society of Toxicologic Pathology (STP) Immunotoxicology Working Group (P. HALEY et al.), STP Position
Paper: Best Practice Guideline for the Routine Pathology Evaluation of the Immune System, Toxicologic
Pathology, 33:404-407, 2005.
11. U.S. Department of Health and Human Services, Food and Drug Administration, Center for Drug
Evaluation Research, Draft Guidance for Industry on Computerized Systems Used in Clinical Trials; Availability,
The Federal Register, 69(191):59239-59240, October 4, 2004.
12. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances (OPPTS),
Health Effects Test Guidelines, OPPTS 870.4100: Chronic Toxicity, 1998.
13. U.S. National Academy of Sciences (NAS), National Research Council (NRC), Institute of Laboratory
Animal Resources, Guide for the Care and Use of Laboratory Animals, National Academy Press, Washington,
D.C., 1996.
14. U.S. NAS, NRC, Subcommittee on Laboratory Animal Nutrition, Committee on Animal Nutrition, Board on
Agriculture, Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, National Academy Press,
Washington, D.C., 1995.
Links on this page:
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ntsandPackaging/Redbook/ucm078409.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078409.htm
7. 	http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?
c=ecfr&sid=f88db9c353f2a7715387dcf2b476e933&rgn=div5&view=text&node=21:1.0.1.1.22&idno=21
8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078323.htm
9. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
10. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
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November 2003
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Long-term, one-year toxicity tests with non-rodents (usually dogs) should be conducted for a minimum of 12
months (one year). Results of these tests can be used to (1) characterize the toxicity of the test substance in
non-rodents and (2) determine the dose of the test substance that produces no observed adverse effects
(NOEL or NOAEL) for some toxicological endpoints. One-year toxicity tests are not conducted for the purpose
of assessing carcinogenicity, although data from these tests may reveal information about the carcinogenicity
of the test substance. The following guideline is written for dogs, if other non-rodents are used, modificaitons
to the guidline may be necessary. Sponsors/submitters of petitions/notifications are encouraged to also
become familiar with the Guidance for Reporting Results of Toxicity Studies (Chapter IV.B.2.), Pathology
Considerations in Toxicity Studies (Chapter IV.B.3.), and Statistical Considerations in Toxicity Studies
(Chapter IV.B.4.) during the development of study design.
Scientifically justified changes to the 1993 draft "Redbook II" version of this section have been made following
consultation with other authoritative guidelines and publications 1-7
.
Nonclinical laboratory studies must be conducted according to U.S. FDA good laboratory practice (GLP)
regulations, issued under Part 58. Title 21. Code of Federal Regulations. This document may be obtained from
the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402, (toll free 866-
512-1800).
Redbook 2000: IV.C.5.b One-Year Toxicity Studies with Non-Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.5.b. One-Year Toxicity Studies with Non-Rodents
I. Good Laboratory Practice
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.5.b One-Year Toxicity Studies with Non-Rodents
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Recommendations about the care, maintenance, and housing of animals contained in NIH publication 85-23,
"Guide for the Care and Use of Laboratory Animals"7
, and the DHEW publication no. 78-23 should be followed
unless they conflict with specific recommendations in these guidelines. Additionally, dogs should receive
appropriate vaccinations prior to commencement of the study.
These guidelines are for studies with dogs. If other non-rodent species are used, modifications of these
guidelines may be necessary. Both male and female test animals, that are healthy and have not been
subjected to previous experimental procedures should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting non-rodent species, i.e., dogs, for toxicity studies.
Additionally, it is important that test animals come from well-characterized and healthy colonies and should be
selected so that they are likely to achieve the recommended duration of the study.
Dogs should be obtained so that, following an appropriate time of acclimation, dosing begins when animals are
no older than 4 to 6 months of age.
Equal numbers of male and female dogs should be used in one-year toxicity studies. Experimental and control
groups should have at least 4 dogs per sex per dose group at the beginning of the study. If interim necropsies
are planned, the number of dogs per sex per group should be increased by the number scheduled to be
sacrificed before completion of the study. These recommendations will help ensure that the number of animals
that survive until the end of the study will be sufficient to permit a meaningful evaluation of toxicological
effects.
Generally, it is not possible to treat animals for infection during the course of a study without risking
interaction between the compound used for treatment and the test substance. This interaction may confound
or complicate the interpretation of study results.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal must be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tatoo).
Animals should be housed one per cage or run (single-caged). This recommendation reflects three principal
concerns:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses and determining whether decreases in body weight
gain are due to decreased palatability or substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
In general, feed and water should be provided ad libitum to animals in toxicity studies, and the diets for these
studies should meet the nutritional requirements of the species 3-6 for normal growth and reproduction.
Unless special circumstances apply which justify otherwise, care should be taken to ensure that the diets of
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species, Strains and Sex:
C. Age:
D. Number and Sex:
E. Infected Animals:
F. Animal Identification:
G. Caging:
H. Diet:
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the compound treated groups of animals are isocaloric (equivalent in caloric density) with and contain the
same levels of nutrients (e.g., fiber, micronutrients) as the diets of the control group. Unrecognized or
inadequately controlled dietary variables may result in nutritional imbalances or caloric deprivation that could
confound interpretation of the toxicity study results (e.g., lifespan, background rates of tumor incidences) and
alter the outcome and reproducibility of the studies.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. It is important that feed consumption of animals be as closely and accurately monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, paired feeding can be used to eliminate the differences in consumption between
control and compound treated groups. When a paired feeding study design is to be employed, pairs of animals
of the same sex, age, and approximate size are selected and fed the control or the experimental diet. Animals
should be single-caged so that feed consumption can be determined daily, and the control animal is then fed
an amount of food equal to that which the paired experimental animal ate on the preceding day. If the test
substance is non-nutritive and composes a significant proportion of the diet, the pair-fed control animals
should be fed an amount of its feed such that it consumes a nutritionally equivalent amount of diet as the
paired experimental animal. Additionally, the study should include a second group of control animals fed the
normal ration amount to ensure that the impact on any observed experimental result is due to differences in
energy or nutrient intake.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
It may be preferable to use a semi-purified diet prepared with known amounts of well-characterized
ingredients for short-term and subchronic toxicity studies because of batch to batch variations in diet
composition (e.g., fiber, mineral, vitamins, isoflavones) in some of the commonly used laboratory animal
chows. The use of these semi-purified diets, however, may not be advisable in long-term and reproductive
studies due to inadequate historical data related to their influences on animal survival and toxicological
endpoints. For example, loss of necessary but unidentified micronutrients in the semipurified diet may
interfere with normal reproduction.
Related issues are discussed in the section on Diets for Toxicity Studies in Chapter IV.B.5. in the 1993 draft
"Redbook II"
Animals should be assigned to control and compound treated groups in a stratified random manner; this will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups (for example: mean body weights and body weight ranges). If other characteristics are used as the
basis for randomization then that characterization should be described and justified.
Animals in all groups should be placed on study on the same day; if this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. If the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be cause to repeat the study.
I. Assignment of Control and Compound Treated Animals:
J. Mortality:
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For example, under normal circumstances, mortality in the control group should not exceed 10%.
Adequate animal husbandry practices should result in considerably less than 10% of animals and tissues or
organs lost to a study because of autolysis. Autolysis in excess of this standard may be cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis but not so low as to cause cell damage. If
histopathological examination is to be conducted, tissue specimens should be taken from the animals and
placed in appropriate fixatives when the necropsy is performed.
The test substance used in toxicity studies should be the same substance that the
petitioner/notifier intends to market. A single lot of test substance should be used throughout the study,
when possible. Alternatively, lots that are similar in purity and composition should be used.
The identity of the test substance or mixture of substances to be tested should be known. We urge
petitioners/notifiers to consult with the Agency in determination of test compound and to provide a Chemical
Abstract Service (CAS) Registry Number or Numbers.
The composition of the test substance should be known, including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test sample should be stored under conditions that maintain its stability, quality, and purity until the
studies are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
Animals should be exposed to the test substance 7 days per week for at least 52 weeks (one year).
The route of administration of the test substance should approximate that of normal human exposure, if
possible. For food ingredients (e.g., food and color additives) the oral route of administration is preferred. A
justification should be provided when other routes are used. The same method of administration should be
used for all test animals throughout the study.
The test substance should be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
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z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form (e.g., in
soft drinks, beer), or if administration in the diet is inappropriate for other reasons. The amount of test
substance administered in drinking water should be expressed as mg of test substance per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of single, large doses instead of continual
ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier should
provide information that can allow the reviewer to conclude that administration of the test compound by
encapsulation or gavage is equivalent in all toxicologically important respects to administration in the
diet or drinking water. Alternatively, metabolic information on both modes of administration should be
provided so that appropriate interpretation of data can be accomplished.
A minimum of three dose levels of the test substance should be used per sex (one dose level per group). A
concurrent control group should be included in the study.
Dose selection for toxicity studies should be based on information related to the toxicity of the test substance.
Information from 90-day toxicity studies in non-rodents can help determine appropriate doses for the one-
year toxicity study in non-rodents (see Chapter IV.C.4.b.).
A minimum of three dose levels of the test substance and a concurrent control group should be used in
toxicity studies. When designing and conducting toxicity studies the following should be considered: 1) the
high dose should be sufficiently high to induce toxic responses in test animals; 2) the low dose should not
induce toxic responses in test animals; and 3) the intermediate dose should be sufficiently high to elicit
minimal toxic effects in test animals (such as alterations in enzyme levels or slight decreases in body weight
gains). No dose should cause an incidence of fatalities that prevents meaningful evaluation of the data.
Administration of the test substance to all dose groups should be done concurrently.
A concurrent control group of test animals is required. The control group in dietary studies should be fed the
basal diet. Exceptions to this and other related information, including a discussion regarding pair-feeding, was
provided above in section "II Test Animals, H. Diet".
A carrier or vehicle for the test substance should be given to control animals at a volume equal to the
maximum volume of carrier or vehicle given to any dosed group of animals. Sufficient toxicology information
should be available on the carrier or vehicle to ensure that its use will not compromise the results of the
study. If there is insufficient information about the toxic properties of the vehicle used to administer the test
substance, an additional control group that is not exposed to the carrier or vehicle should be included. In all
other respects, animals in the control group should be treated the same as animals in dosed groups. (See
additional information in section "II Test Animals, H. Diet" above.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are compliant with Good Laboratory Practice
principles. 8
Routine cage-side observations should be made on all animals at least once or twice a day throughout the
study for general signs of pharmacologic and toxicologic effects, morbidity and mortality. The usual interval
between observations should be at least 6 hours. Individual records should be maintained for each animal and
the time of onset and the characteristics and progression of any effects should be recorded, preferably using a
scoring system.
An expanded set of clinical evaluations, performed inside and outside of the cage, should be carried out in
C. Dose groups:
1. Selection of Treatment Doses:
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
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short-term and subchronic toxicity studies in rodents and non-rodents, in one-year non-rodent toxicity
studies, and reproductive toxicity studies in rodents to enable detection not only of general pharmacologic and
toxicologic effects but also of neurologic disorders, behavioral changes, autonomic dysfunctions, and other
signs of nervous system toxicity. Specific information about the systematic clinical tests/observations is
contained in Chapter IV.C.10. This expanded set of clinical examinations (Chapter IV.C.10), conducted inside
and outside the cage, should be age appropriate and performed on all animals at least once prior to initiation
of treatment, and periodically during treatment. Signs noted should include, but not be limited to, changes in
skin, fur, eyes, mucous membranes, occurrence of secretions and excretions or other evidence of autonomic
activity (e.g., lacrimation, piloerection, pupil size, unusual respiratory pattern). Additionally, changes in gait,
posture and response to handling, as well as the presence of clonic or tonic seizures, stereotypes (e.g.,
excessive grooming, repetitive circling) or bizarre behavior (e.g., self-mutilating, walking backwards) should
be recorded. Tumor development, particularly in long-term studies, should be followed: the time of onset,
location, dimensions, appearance and progression of each grossly visible or palpable tumor should be
recorded. During the course of a study, toxic and pharmacologic signs may suggest the need for additional
clinical tests or expanded post-mortem examinations.
Test animals should be weighed at least once a week. Feed consumption (or water consumption if the test
substance is administered in the drinking water) should be measured every week during the one-year toxicity
study. Petitioners should use this information to calculate intake of the test substance during each week of the
study. Petitioners should also attempt to quantify spillage of feed by test animals, and to determine if spillage
is greater with test diets than with control diets. Appropriate discussions of feed spillage should be included in
the study report.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed as described in the following sections:
1. 	Opthalmological Examination: 	This examination should be performed by a qualified individual on all
animals before the study begins and on control and high-dose animals at the end of the study. If the
results of examinations at termination indicate that changes in the eyes may be associated with
administration of the test substance, ophthalmological examinations should be performed on all animals
in the study.
2. 	Hematology: 	Blood samples should be obtained from all animals of all groups at the following times:
prior to initiation of treatment, during the first two weeks on study (receiving treatment), at 3-month
intervals during the study, and at termination. The determination of the second sampling time point
should be based on the expected time of initial toxicological effects on the organ systems. Blood samples
should be analyzed individually, and not pooled. Blood should be drawn at approximately the same time
each sampling day.
1. 	The following determinations are recommended:
1. 	hematocrit
2. 	hemoglobin concentration
3. 	erythrocyte count
4. 	total and differential leukocyte counts
5. 	mean corpuscular hemoglobin
6. 	mean corpuscular volume
7. 	mean corpuscular hemoglobin concentration
8. 	and a measure of clotting potential (such as clotting time, prothrombin time, thromboplastin
time, or platelet count).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures
should be employed so that evaluations of reticulocyte counts and bone marrow cytology may be
performed if warranted. Reticulocyte counts should be obtained for each animal using automated
reticulocyte counting capabilities, or from air-dried blood smears. Bone marrow slides should be
prepared from each animal for evaluating bone marrow cytology. These slides would only need to be
examined microscopically if effects on the hematopoietic system were noted.
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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Clinical Chemistry: 	Blood samples should be obtained from all animals of all groups at the following
times: prior to initiation of treatment, during the first two weeks on study (receiving treatment), at 3-
month intervals during the study, and at termination. The determination of the second sampling time
point should be based on the expected time of initial toxicological effects on the organ systems. Dogs
should be fasted overnight and blood drawn for clinical chemistry tests before feeding. Blood samples
should be analyzed individually, and not pooled. Blood should he drawn at approximately the same time
each sampling day.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, carbohydrate metabolism, and liver and kidney function. Specific determinations should
include:
1. 	Hepatocellular evaluation: select at least 3 of the following 5
1. 	alanine aminotransferase (SGPT, ALT)
2. 	aspartate aminotransferase (SGOT, AST)
3. 	sorbitol dehydrogenase
4. 	glutamate dehydrogenase
5. 	total bile acids
2. 	Hepatobiliary evaluation: select at least 3 of the following 5
1. 	alkaline phosphatase
2. 	bilirubin (total)
3. 	gamma-glutamyl transpeptidase (GG transferase)
4. 	5' nucleotidase
5. 	total bile acids
3. 	Other markers of cell changes or cellular function
1. 	albumin
2. 	calcium
3. 	chloride
4. 	cholestrol(total)
5. 	cholinesterase
6. 	creatinine
7. 	globulin (calculated)
8. 	glucose (in fasted animals)
9. 	phosphorous
10. 	potassium
11. 	protein (total)
12. 	sodium
13. 	triglycerides (fasting)
14. 	urea nitrogen
1. 	However, when adequate volumes of blood cannot be obtained from test animals, the following
determinations should generally be given priority. FDA understands that the specific nature of the
test compound may warrant the consideration of alternative tests. Appropriate justification for
alternative tests should be presented in study reports.
1. 	alanine aminotransferase
2. 	alkaline phosphatase
3. 	chloride
4. 	creatinine
5. 	gamma-glutamyl transpeptidase (GG transferase)
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6. 	glucose (in fasted animals)
7. 	potassium
8. 	protein (total)
9. 	sodium
10. 	urea nitrogen
Additional clinical chemistry tests may be recommended to extend the search for toxic effects
attributable to a test substance. The selection of specific tests will be influenced by observations on the
mechanism of action of the test substance. Clinical chemistry determinations that may be recommended
to ensure adequate toxicological evaluation of the test substance include analyses of acid/base balance,
hormones, lipids, methemoglobin, and proteins.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe
considerable variation in the results of clinical chemistry analyses from day to day9 . Ideally, clinical
chemistry analyses for all dose groups should be completed during one day. If this is not possible,
analyses should be conducted in such a way as to minimize potential variability.
4. 	Urinalyses: A timed urine-volume collection should take place prior to dosing, at 3-month intervals, and
at the end of the study for all animals in the study. The volume of urine collected, specific gravity, pH,
glucose, and protein should be determined as well as conducting a microscopic evaluation of urine for
sediment and presence of blood/blood cells 10 .
5. 	Neurotoxicity Screening/Testing : Screening for neurotoxic effects should be routinely carried out in
dogs and other non-rodents (preferably miniature swine). The neurotoxicity screen should be age
appropriate and would typically include: (1) specific histopathological examination of tissue samples
representative of major areas of the brain, spinal cord, and peripheral nervous system (see organs and
tissues listed below under VI.C. Preparation of Tissues for Microscopic Examination) and (2) a functional
battery of quantifiable observations and manipulative tests selected to detect signs of neurological,
behavioral, and physiological dysfunctions. This functional battery is also referred to as an expanded set
of clinical evaluations and is described more fully in section V.A. Observations of Test Animals in this
chapter and in Chapter IV.C.10. Neurotoxicity Studies.
Reports of one-year toxicity studies should include an assessment of the potential for the test substance
to adversely affect the structural or functional integrity of the nervous system. This assessment should
evaluate data from the neurotoxicity screen and other toxicity data from the study, as appropriate.
Based on this assessment, the petitioner should make an explicit statement about whether or not the
test substance presents a potential neurotoxic hazard and if additional neurotoxicity testing is deemed
appropriate. FDA recommends that additional neurotoxicity testing not be undertaken without first
consulting with the Agency.
6. 	Immunotoxicity: Results from tests that are included in the list of primary indicators for immune
toxicity (see Chapter V.C. of the 1993 draft "Redbook II") should also be evaluated as part of an
immunotoxicity screen. Reports of one-year toxicity tests should include an assessment of the potential
for the test substance to adversely affect the immune system. This assessment should evaluate data
from the list of primary indicators included in the immunotoxicity screen and other toxicity data from the
study, as appropriate. Based on this assessment, the petitioner/notifier should make an explicit
statement about whether or not the test substance presents a potential immunotoxic hazard which
requires further immunotoxicity testing. Additional immunotoxicity tests are discussed in Chapter V.C. of
the 1993 draft "Redbook II" but should not be undertaken without first consulting with the Agency.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination (see below).
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
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thyroid/parathyroid, thymus, ovaries and uterus. Organs should be carefully dissected and trimmed to remove
fat and other contiguous tissue and then be weighed immediately to minimize the effects of drying on organ
weight.
Generally, the following tissues should be fixed in 10% buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
1. 	adrenals
2. 	aorta
3. 	bone (femur)
4. 	bone marrow (sternum)
5. 	brain (at least 3 different levels)
6. 	cecum
7. 	colon
8. 	corpus and cervix uteri
9. 	duodenum
10. 	epididymis
11. 	esophagus
12. 	eyes
13. 	gall bladder (if present)
14. 	heart
15. 	ileum
16. 	jejunum
17. 	kidneys
18. 	liver
19. 	lung (with main-stem bronchi)
20. 	lymph nodes (1 related to route of administration and 1 from a distant location)
21. 	mammary glands
22. 	nasal turbinates
23. 	ovaries and fallopian tubes
24. 	pancreas
25. 	pituitary
26. 	prostate
27. 	rectum
28. 	salivary gland
29. 	sciatic nerve
30. 	seminal vesicle (if present)
31. 	skeletal muscle
32. 	skin
33. 	spinal cord (3 locations: cervical, mid-thoracic, lumbar)
34. 	spleen
35. 	stomach
36. 	testes
37. 	thymus (or thymic region)
38. 	thyroid/parathyroid
39. 	trachea
40. 	urinary bladder
C. Preparation of Tissues for Microscopic Examination
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
41. 	vagina
42. 	all tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then the next lower dose
level tested of those specific tissues should be examined. Successive examination of the next lower dose level
continues until no effects are noted. In addition, all tissues from animals which died prematurely or were
sacrificed during the study should be examined microscopically to assess any potential toxic effects.
Histopathological evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V. C. of the 1993 draft "Redbook II") for all animals.
1. 	EPA Health Effects Test Guidelines OPPTS 870.4100, Chronic Toxicity, August 1998
2. 	Kurt Weingand et. al., Harmonization of Animal Clinical Pathology Testing in Toxicity and Safety Studies,
Fundamental and Applied Toxicology 29, pp 198-201, 1996
3. 	Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, Subcommittee on Laboratory
Animal Nutrition, Committee on Animal Nutrition, Board on Agriculture, National Research Council, 1995.
4. 	Nutrient Requirements of Dogs, Revised, Committee on Animal Nutrition, National Research Council,
1985.
5. 	Nutrient Requirements of Swine: 10th Revised Edition, Subcommittee on Swine Nutrition, Committee on
Animal Nutrition, National Research Council, 1998.
6. 	Nutrient Requirements of Rabbits, Second Revised Edition, Committee on Animal Nutrition, National
Research Council, 1977.
7. 	National Research Council Institute of Laboratory Animal Resources. 1996. Guide for the Care and Use
of Laboratory Animals. National Academy Press, Washington, DC.
8. 	The Application of the Principles of GLP to Computerised Systems, Organisation for Economic
Cooperation and Development (OECD), Environmental Monograph No. 116, Paris, 1995.
9. 	Gaylor, D.W., Suber, R.L., Wolff, G.L. and Crowell, J.A. (1987) Statistical variation of selected clinical
pathological and biochemical measurements in rodents (42555) Proc. Soc. Exp. Biol. Med. , 185:361-367
10. 	Ragan, H.A. and Weller, R.E., "Markers of Renal Function and Injury" in The Clinical Chemistry of
Laboratory Animals, Second Edition 1999, Taylor&Francis, Philadelphia, PA, pp. 520-533
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
Links on this page:
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January 2006
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic.
Scientifically justified changes to the 1993 "draft" Redbook version of this section have been made following
consultation with other authoritative guidelines and publications.
Carcinogenicity studies (bioassays) in two rodent species (usually rats and mice) are recommended for food
ingredients with the highest levels of concern (e.g.,Concern Level III direct food additives, food contact
substances with cumulative exposure at or greater than 1 ppm). The carcinogenicity studies (preferably in
rats) may be combined with chronic toxicity studies (see Chapter IV.C.7). The Agency recommends that in
utero exposure be included in carcinogenicity studies due to the fact that exposure to food ingredients occurs
during all stages of life (more information is included in Chapter IV.C.8). These studies are designed to
determine whether a food ingredient possesses carcinogenic activity when administered to rodents in regularly
repeated oral doses for the "lifetime" of the test animal.
Nonclinical laboratory studies discussed in this chapter should be conducted according to U.S. FDA good
laboratory practice (GLP) regulations, issued under Part 58 Title 21 Code of Federal Regulations. This
document may be obtained from the Superintendent of Documents, U.S. Government Printing Office,
Washington, D.C., 20402, (toll free 866-512-1800). Studies performed under other international/national
guidelines may be considered equivalent to those conducted under U.S. FDA GLP regulations. Specific area(s)
of non-compliance with FDA GLP regulations should be discussed and justified.
Redbook 2000: IV.C.6 Carcinogenicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.6. Carcinogenicity Studies with Rodents
I. Good Laboratory Practice
II. Test Animals
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.6 Carcinogenicity Studies with Rodents
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Recommendations about the care, maintenance, and housing of animals contained in the National Research
Council, Guide for the Care and Use of Laboratory Animals should be followed unless they conflict with specific
recommendations in this chapter.
Guidelines contained within this chapter are for studies with mice and rats; if other rodent species are used,
modifications may be necessary. Both male and female test animals, which are healthy and have not been
subjected to previous experimental procedures, should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies. The selection of inbred, out-bred, or hybrid rodent strains for toxicity tests should be based upon the
scientific questions to be answered. Additionally, it is important that test animals come from well-
characterized and healthy colonies. Because recent information suggests survivability problems exist for some
strains of rats, test animals should be selected that are likely to survive for the recommended duration of the
study (see discussions under sections II.D: Number and Sex and IV.A: Duration of Testing). The Agency
encourages petitioners/notifiers to consult with Agency scientists before toxicity testing has begun if they have
questions about the appropriateness of a particular species, strain, or substrain.
Another Center within the Agency (Center for Drug Evaluation and Research), as part of a pilot program,
accepts safety data from six month studies employing genetically modified mice (i.e., transgenic mice) as a
replacement for one of the rodent carcinogenicity studies5 . The Office of Food Additive Safety will consider
this type of information only as supplemental data but does not consider such studies to be substitutes for the
two (2-year) rodent carcinogenicity bioassays. Data from transgenic rodent carcinogenesis or mutagenesis
assays may be useful in evaluating compound-specific questions relating to mechanism of action or tissue
distribution. For the determination of carcinogenic risk of certain kinds of food ingredients (i.e., constituents
and/or contaminants), the transgenic mouse model is inappropriate in that it does not provide quantitative
dose-response data. It also has not, as of this date, been fully validated or accepted by most national and
international validation organizations (e.g., Scientific Advisory Committee on Alternative Toxicological Method
of the Interagency Coordinating Committee on the Validation of Alternative Methods 12 ) or testing laboratories.
At this time, there is no large repository of historical control data to establish baseline parameters. Given the
nature of consumption patterns of food ingredients (i.e., chronic, lifetime exposures), it is necessary to require
the chronic safety testing of food ingredients that would be representative of lifetime exposure in humans, in
addition to requiring that only quantitative data derived from fully validated test systems be used in their
safety assessment.
Dosing of rodents should begin after weaning, and following a suitable acclimation period of at least 5 days,
and before they are approximately 6-8 weeks old.
Experimental and control groups should have a sufficient number of animals at the beginning of the study to
ensure that at least 25 rodents per sex per group survive to the end of the study. Having sufficient animals
survive to the end of the study allows for objective assessment of test substance-related tumor development.
Survival can be improved by reducing non-compound related animal pathology, which may occur as a result of
excessive weight gain (e.g., obesity-related pituitary changes), or as sequelae to other stressors (e.g.,
parasitic infection).
The Agency recommends that petitioners/notifiers carefully consider their choice of rat strains for
carcinogenicity bioassays, since some strains have more serious problems with survivorship than other
strains. It is recommended that carcinogenicity studies begin with at least 50 animals per sex per group.
Petitioners/notifiers are encouraged to begin bioassays with more than 50 animals per sex per group if
survivorship is expected to be a problem with the rat strain used in the study. If fewer than 25 animals per
sex per group are expected to survive to the end of the study (24 months, see section IV.A: Duration of
Testing), petitioners/notifiers should take particular care to ensure and document early detection of dead
animals through attentive and frequent cage-side observations, thus minimizing the loss of tissues from
autolysis. In addition, they should consult with the Agency as soon as a problem with survivorship in a
carcinogenicity study becomes apparent.
A. Care, Maintenance and Housing:
B. Selection of Species and Strains:
C. Age (start of dosing):
D. Number and Sex:
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If interim necropsies are planned, the total number of rodents of each sex per group should be increased by
the number scheduled to be sacrificed before completion of the study. A minimum of 10 rodents per sex per
group should be available for each interim necropsy.
Generally, it is not possible to treat animals for infection during the course of a study without the possibility of
interaction between the compound used for treatment and the test substance. This interaction may seriously
confound or complicate the interpretation of study results. 	However, if problems with infection do occur, the
sponsor for the study should use their best judgment in proceeding with the study and inform the Agency of
their decision. In addition, the Agency requests that they provide a full and detailed description of the
justification and possible implications of the infection, and if applicable, the justification and possible
implications for treatment of the infection.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal should be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tattoo).
Animals should be housed one per cage. This recommendation reflects three points of consideration:
z The amount of feed consumed by each animal in the study cannot be determined when more than one
animal is housed in each cage. This information is necessary in the determination of feed efficiency
(relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses in determining whether decreases in body weight gain
are due to decreased palatability or test substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost due to
cannibalism.
In general, feed and water should be provided ad libitum, and the diets should meet the nutritional
requirements for the species13 for normal growth and longevity. Unless special circumstances apply which
justify otherwise, care should be taken to ensure that the diets of the test substance treated groups of
animals contain the same levels of calories and nutrients (e.g., fiber, micronutrients) as the diets of the
control group. Inadequately controlled dietary variables may result in nutritional imbalances or caloric
deprivation that could confound interpretation of the toxicity study results (e.g., lifespan, background rates of
tumor incidences) and alter the outcome and reproducibility of the studies. However, the Agency is also aware
of some beneficial effects on the survivability of certain animal species that have been on calorie-
restricted 14,24 , or low-protein diets 15,16 . The Agency may accept such study results if the sponsor provides
sufficient historical control data on the diet, and the study is well-conducted.
The following issues are important to consider when establishing diets for animals in carcinogenicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test substance doses than
expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed groups
to compensate for the differences in energy and nutrient content of the high dose diets. Such circumstances
make it especially important that feed consumption of these animals be as accurately and closely monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, other feeding regimens or experimental designs may be necessary. Consultation
E. Infected Animals:
F. Animal Identification:
G. Caging:
H. Diet:
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with the Agency is recommended when alternatives are being considered.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
Appropriate levels of nutrient fortification should be determined experimentally.
Other related issues (e.g., advantages and disadvantages of using natural ingredient versus purified diets) are
discussed in the National Research Council publication on nutrient requirements of laboratory animals13 .
Animals should be assigned to control and compound treated groups in a stratified random manner. This will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups. In general, mean body weights and/or body weight ranges are used as a basis of randomization. If
other characteristics are used as the basis for randomization, they should be described and justified.
Animals in all groups should be placed on study on the same day. If this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. When the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be a cause to repeat the study.
Adequate animal husbandry practices should result in considerably less than 10 % loss of animals and tissues
or organs in a study because of autolysis. Autolysis in excess of this standard may be a cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis (i.e., between 4o
C and 8 o
C), but not so low as to cause
cell damage. If histopathological examination is to be conducted, tissue specimens should be taken from the
animals and placed in appropriate fixatives when the necropsy is performed.
The test substance used in carcinogenicity studies should be the same substance that the petitioner/notifier
intends to market or, when appropriate, the test substance may be a constituent chemical or an impurity. A
single lot of test substance should be used throughout the study. When this is not possible, lots that are as
similar as possible in purity and composition should be used. It is the responsibility of the petitioner/notifier
to notify the animal test facility of the purity of the test substance, as well as the identity and concentration of
any impurities that might be present.
The identity of the test substance or mixture of substances to be tested should be known. We urge the
petitioners/notifiers to consult with the Agency regarding the determination of the test compound, and to
provide all relevant Chemical Abstract Service (CAS) Registry numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test samples should be stored under conditions that maintain their stability and purity until the studies
are complete.
I. Assignment of Control and Compound Treated Animals:
J. Mortality:
K. Autolysis:
L. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
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The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
The test animal should be exposed to the test substance 7 days per week for 104 consecutive weeks (two
years), or for the life span of the animal. In general, the Agency does not recommend early termination of
carcinogenicity studies due to decreased survivorship (see section II.D: Number and Sex). Carcinogenicity
bioassays should be conducted for a major portion of the test animal's lifetime. While it is desirable to have
an optimum number of animals survive to the end of the study, the Agency believes there is more benefit, as
well as added sensitivity, to be gained by conducting carcinogenicity bioassays for as long as possible, or for
the full 24 months that is recommended in these guidelines.
The route of administration of the test substance should approximate that of normal human exposure, and if
possible, the oral route should be used. A justification should be provided when using other routes. The same
method of administration should be used for all test animals throughout the study. The test substance should
be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid foods
or a combination of solid and liquid foods. If the test substance is added to the diet, animals should not
be able to selectively consume either basal diet or test substance in the diet on the basis of color, smell,
or particle size. If the compound is mixed with ground feed and pelleted, nothing in the pelleting process
should affect the test substance (for example, heat-labile substances may be destroyed during pellet
production by a steam process). When the test substance is administered in the diet, dietary levels
should be expressed as mg of the test substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form by humans
(for example, in soft drinks or beer), or if administration in the diet of rodents is inappropriate. The
amount of test substance administered in drinking water should be expressed as mg of test substance
per ml of water.
z By encapsulation or oral intubation (gavage), if the two previous methods are unsatisfactory or if
human exposure is expected to be through daily ingestion of a single, large bolus dose instead of
continual ingestion of small doses. If the test substance is administered by gavage, it should be given at
approximately the same time each day. The maximum volume of solution that can be given by gavage in
one dose depends on the test animal's size; for rodents, the volume ordinarily should not exceed 1
ml/100 g body weight. If the gavage vehicle is oil, then the volume should be no more than 0.4 ml/100
g of body weight, and the use of a low-fat diet should be considered. If the test substance should be
given in divided doses, all doses should be administered within a 6 hour period. Doses of test substance
administered by gavage should be expressed as mg of test substance per ml of gavage vehicle. Finally,
the petitioner/notifier should provide information that can allow the Agency to conclude that
administration of the test compound by encapsulation or gavage is equivalent in toxicologically important
respects to administration in the diet or drinking water. Alternatively, metabolic information on both
modes of administration should be provided so that appropriate interpretation of data can be
accomplished.
Dose selection for long-term toxicity studies should be based on results from subchronic studies and other
related test substance information.
Three to five dose levels of the test substance and a concurrent control group should be used in
carcinogenicity bioassays. When designing and conducting carcinogenicity bioassays the following should be
considered: 1) the high dose (maximum tolerated dose) should be sufficiently high to induce toxic responses
in test animals, and should not cause fatalities high enough to prevent meaningful evaluation of the data from
the study; 2) the low dose should not induce toxic responses in test animals; and 3) the intermediate dose(s)
should be sufficiently high to elicit minimal toxic effects in test animals (such as alterations in enzyme levels
D. Expiration Date:
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
C. Dose groups:
1. Selection of Treatment Doses:
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or slight decreases in body weight gains. Administration of the test substance to all dose groups should be
done concurrently (see Section II.I: Assignment of Control and Compound Treated Animals).
High Dose: The high dose should be the maximum tolerated dose (MTD).
It is not acceptable to select doses for carcinogenicity bioassays based on information unrelated to the toxicity
of the test substance. For example, the highest dose in a carcinogenicity study should not be selected so as
to provide a pre-determined margin of safety over the maximum expected human exposure to the test
substance, assuming that the results of testing at that dose will be negative.
These guidelines recommend that the highest dose in carcinogenicity bioassays should be the MTD. In
evaluating the results of carcinogenicity bioassays of a substance in food, Agency scientists will consider the
question of whether the substance was tested at the MTD as one of several factors that may affect
interpretation of the results of the bioassay. The bioassay should include a description of the process used to
select the MTD for the study.
The MTD is defined by the National Toxicology Program (NTP) as "that dose which, when given for the
duration of the chronic study as the highest dose, will not shorten the treated animals' longevity from any
toxic effects other than the induction of neoplasms"17 The Office of Science and Technology Policy provides
the following advice, "The highest dose should be selected after an adequate prechronic study and after
evaluating other relevant information, as necessary, to determine the highest dose consistent with predicted
minimal target organ toxicity and normal life span, except as a consequence for the possible induction of
cancer."18 	In addition, the NTP cautions that the MTD should not cause morphologic evidence of toxicity of a
severity that would interfere with the interpretation of the study results.17
In general, the MTD is estimated following a careful analysis of data from appropriate subchronic toxicity
tests. As the scientific community's experience with toxicity testing has accumulated, the need to consider a
broad range of biological information when selecting the MTD has become increasingly clear. For example,
data concerning changes in body and organ weight and clinically significant alterations in hematological,
urinary and clinical chemistry measurements, in combination with more definitive toxic, gross or
histopathologic endpoints, can be used to estimate the MTD.
Although the high dose in a carcinogenicity study should be selected to achieve the MTD, the Agency
recognizes that this goal may not always be met. There are uncertainties in predicting the MTD for long-term
bioassays from the results of shorter-term studies. Because working definitions of the MTD require the use of
scientific judgment, it is sometimes possible for competent investigators looking at the same set of data to
arrive at significantly different estimates of the MTD. Such disagreement may be based on different
interpretations of the results of metabolic studies or different conclusions about whether an organ alteration is
adaptive or toxicological. In situations such as these, when it is unclear what dose of the test substance is the
MTD, the petitioner/notifier should consult with the Agency to determine an appropriate high dose (MTD) for
the carcinogenicity bioassay.
The Agency recognizes that use of the MTD in carcinogenicity bioassays has several advantages; these
include:
z Compensating for the inherent lack of sensitivity of the bioassay, including the relatively small number of
rodents used in the study;
z Providing consistency with other models used in toxicology (e.g., high enough doses should be used in
order to elicit evidence of the presumed toxicity or increase probability of detecting rare tumors and
identifying weak carcinogens); and
z Permitting comparison of carcinogenic potencies of substances tested at the MTD, even when the data
are collected from different studies 19 .
The Agency acknowledges that its recommendation to conduct carcinogenicity studies at the MTD may result
in the use of doses that are so high as to be unrepresentative of the toxicity of the test substance at lower
doses in animals or humans. For example, excessively high doses of a test substance can saturate enzyme
systems involved in detoxification of the test substance. Given the above, after thorough internal assessment
and in an agreement with other authoritative bodies 9,10 , the Agency concludes that the MTD is still the best
choice for selecting the high dose for carcinogenicity studies. It should be noted that this is also in line with
the conclusions of the International Conference on Harmonization which recommends the use of the MTD in
choosing the high dose for drug safety testing 7,8 .
Low Dose:
The low dose level should not interfere with the normal growth, development, and lifespan of test animals, nor
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should it produce any signs of toxicity.
Intermediate Dose:
The intermediate dose should produce minimal signs of toxicity. The exact dose selected as the intermediate
dose may depend on the pharmacokinetic properties of the test substance.
Optional Fourth Dose Level:
If significant differences exist in the pharmacokinetic or metabolic profiles of the test substance administered
at high and low doses, an optional (fourth) dose level may be included in the study. This dose level should be
the highest dose that produces a pharmacokinetic or metabolic profile similar to profiles obtained at lower
doses. The number of test animals in the optional group should be selected to provide approximately the
same sensitivity for the detection of the carcinogenic effects of the test substance as the higher dose group
provides.
A concurrent control group of test animals fed the basal diet is required. A carrier or vehicle for the test
substance should be given to control animals at a volume equal to the maximum volume of carrier or vehicle
given to any dosed group of animals. Sufficient toxicology information should be available on the carrier or
vehicle to ensure that its use will not compromise the results of the study. If there is insufficient information
about the toxic properties of the vehicle used to administer the test substance, an additional control group
that is not exposed to the carrier or vehicle should be included. In all other respects, animals in the control
group should be treated the same as animals in dosed groups. (See also section II.H: Diet.)
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are consistent with the intention of the Good
Laboratory Practice principles 20 . The FDA has endorsed the use of the Standard for Exchange of Nonclinical
Data (SEND) format for electronic transmission of animal study data. Contact the Agency for more information
on this electronic protocol.
Routine cage-side observations should be made on all animals inside the cage once or twice a day throughout
the study for signs of departure from normal activity, morbidity and mortality. The usual interval between
multiple periods of observations should be at least 6 hours. Individual records should be maintained for each
animal and, as possible, the onset and progression of any effects should be recorded, preferably using a
scoring system. If grossly visible tumors develop, the following parameters should be recorded; time of
onset, location, dimensions, appearance and progression.
Accurate individual body weight, feed, and water consumption measurements are critical in the objective
evaluation of the effect of a compound on test animals, since changes in these variables are often the first
signs of toxicity. Complete records for these parameters are essential in assessing the time-related
occurrence of toxicity-induced changes. When these data are not carefully recorded the evaluation of the
overall cancer-inducing potential for a test substance may be compromised. A discussion of some of the
variables that affect feed consumption and weight gain/loss can be found under sections II.H: Diet and IV.B:
Route of Administration.
Body weights for all test animals should be recorded weekly for the first 13 weeks, and monthly thereafter for
the duration of the study. Feed consumption (or water consumption if the test substance is administered in
the drinking water) should be measured at the same interval as body weights; petitioners/notifiers should also
attempt to quantify spillage of feed by test animals. When it is suspected that test compound administration
may be affected by any of the following conditions; 1) feed palatability issues, 2) marked changes in body
weight, or 3) increased numbers of animal deaths, the petitioners/notifiers should measure weights and feed
(water) consumption more frequently after the initial 13 week period (e.g., every two weeks).
Petitioners/notifiers should also use this accumulated information to calculate intake of the test substance.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
2. Controls:
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Test Animals:
B. Body Weight and Feed Intake Data:
C. Clinical Testing:
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performed as described in the following sections:
This examination should be performed by a qualified individual on all animals before the study begins and on
control and high-dose animals at the end of the study. If the results of examinations at termination indicate
that changes in the eyes may be associated with administration of the test substance, ophthalmological
examinations should be performed on all animals in the study.
Hematological tests should be performed on at least 10 animals per sex in each group should be made during
the first 2 weeks of study, and at 3, 6 and 12 months during the study. The time of the first sampling may be
based on test results from short-term studies. If data trends or significant parameter changes (biological or
statistical) that are of concern are observed at the 12-month measurement, then an 18-month measurement
should be included. Additional hematology testing should be conducted at the end of the study if data trends
or significant parameter changes are observed at 18 months to be consistent with other clinical testing.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be analyzed
individually, and not pooled. If, due to the large number of animals, it becomes necessary to draw blood
samples on more than one consecutive day at each sampling point, the samples should be obtained at
approximately the same time each day.
The following determinations are recommended: hematocrit, hemoglobin concentration, erythrocyte count,
total and differential leukocyte counts, mean corpuscular hemoglobin, mean corpuscular volume, mean
corpuscular hemoglobin concentration, platelet count, and a measure of clotting potential (e.g., clotting time,
prothrombin time, activated partial thromboplastin time).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures should
be employed so that evaluations of reticulocyte counts and bone marrow cytology may be performed if
warranted. Reticulocyte counts should be obtained for each animal using automated reticulocyte counting
capabilities, or from air-dried blood smears. Bone marrow slides for cytological evaluation should be prepared
from each animal. These slides only need to be microscopically examined when effects on the hematopoietic
system are noted.
Clinical chemistry tests should be performed on at least 10 animals per sex per group during the first 2 weeks
of study, and at 3, 6 and 12 months during the study. The time of the first sampling may be based on test
results from short-term studies. If data trends or significant parameter changes (biological or statistical) that
are of concern are observed at the 12-month measurement, then an 18-month measurement should be
included. Additional clinical chemistry testing should be conducted at the end of the study if data trends or
significant parameter changes are observed at 18 months.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be drawn at
the end of the fasting time and before feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Blood samples should be analyzed individually, and not pooled. If animals are
sampled on more than one day during a study, blood should he drawn at approximately the same time each
sampling day.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, nutrients metabolism, and liver and kidney function. Specific determinations should include:
Hepatocellular evaluation (at least 3 of the following 5)
z Alanine aminotransferase (SGPT, ALT)
z Aspartate aminotransferase (SGOT, AST)
z Sorbitol dehydrogenase
z Glutamate dehydrogenase
z Total bile acids
Hepatobiliary evaluation (at least 3 of the following 5)
z Alkaline phosphatase
z Bilirubin (total)
1. Opthalmological Examination:
2. Hematology:
3. Clinical Chemistry:
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z Gamma-glutamyl transpeptidase (GG transferase)
z 5' nucleotidase
z Total bile acids
Other markers of cell changes or cellular function
z Albumin
z Calcium
z Chloride
z Cholesterol (total)
z Cholinesterase
z Creatinine
z Globulin (calculated)
z Glucose (in fasted animals)
z Phosphorous
z Potassium
z Protein (total)
z Sodium
z Triglycerides (fasting)
z Urea nitrogen
z The Agency understands that the specific nature of the test substance may warrant the consideration of
alternative tests. Appropriate justification for alternative tests should be presented in study reports.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe considerable
variation in the results of clinical chemistry analyses from day to day21 . Ideally, clinical chemistry analyses
for all dose groups should be completed during one day. If this is not possible, analyses should be conducted
in such a way as to minimize potential variability.
The determination of volume of urine collected, urine specific gravity, pH, glucose, and protein, as well as
microscopic analysis of urine for sediment and presence of blood and/or blood cells, are recommended before
dosing, and at 3, 6 and 12 months during the study22 . If data trends or significant parameter changes
(biological or statistical) that are of concern are observed at the 12-month measurement, then an 18-month
measurement should be included. Additional urinalysis testing should be conducted at the end of the study if
data trends or significant parameter changes are observed at 18 months. These tests should be performed on
at least 10 animals per sex per group.
All test animals should be subjected to complete gross necropsy, including examination of external surfaces,
orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should be
performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination.
Organs that should be weighed include the adrenals, brain, epididymides, heart, kidneys, liver, spleen, testes,
thyroid/parathyroid, thymus if present, ovaries and uterus. Before being weighed, organs should be carefully
dissected and trimmed to remove fat and other contiguous tissue. Organs should be weighed immediately
after dissection to minimize the effects of drying on organ weight.
Generally, the following tissues should be fixed in 10 % buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
4. Urinalyses:
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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z Adrenals
z Aorta
z Bone (femur)
z Bone marrow (sternum)
z Brain (at least 3 different levels)
z Cecum
z Colon
z Corpus and cervix uteri
z Duodenum
z Epididymides
z Esophagus
z Eyes
z Gall bladder (if present)
z Harderian gland
z Heart
z Ileum
z Jejunum
z Kidneys
z Liver
z Lung (with main-stem bronchi)
z Lymph nodes (1 related to route of administration and 1 from a distant location)
z Mammary glands
z Nasal turbinates
z Ovaries and fallopian tubes
z Pancreas
z Pituitary
z Prostate
z Rectum
z Salivary gland
z Sciatic nerve
z Seminal vesicle (if present)
z Skeletal muscle
z Skin
z Spinal cord (3 locations: cervical, mid-thoracic, and lumbar)
z Spleen
z Stomach
z Testes
z Thymus (if present)
z Thyroid/parathyroid
z Trachea
z Urinary bladder
z Vagina
z Zymbal's gland
z All tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the animals in the control and high dose
groups should be examined. If treatment related effects are noted in certain tissues, then those specific
D. Microscopic Evaluation
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tissues in the next lower dose level tested should be examined. Successive examination of the next lower dose
level continues until no effects are noted. In addition, all tissues from animals that died prematurely or were
sacrificed during the study should be examined microscopically. If there are questions related to the review
and interpretation of pathological lesions and statistical results, additional discussion may be found in
Chapters IV.B.3 and IV.B.4 of the Redbook 2000.
Histopathology evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V.C. of the 1993 draft Redbook II). A recent publication provides further
discussion on this subject 23
.
1 Organization for Economic Cooperation and Development (OECD), Environment, Health and Safety
Publications, Series on Testing and Assessment No. 35 and Series on Pesticides No. 14, Guidance Notes for
Analysis and Evaluation of Chronic Toxicity and Carcinogenicity Studies, Paris, 2002.
2 OECD, Guideline for Testing of Chemicals, No. 451, Carcinogenicity Studies, Adopted in 1981.
3 National Toxicology Program (NTP)/Department of Health and Human Services (DHHS), Descriptions of NTP
Study Types, 2-Year Study Protocol, 2004.
4 Office of Prevention, Pesticides and Toxic Substances (OPPTS)/United States Environmental Protection
Agency (EPA), Health Effects Test Guidelines, OPPTS 870.4200: Carcinogenicity, 1998.
5 Center for Drug Evaluation Research/Food and Drug Administration (FDA)/DHHS, Guidance for Industry, S1B
Testing for Carcinogenicity of Pharmaceuticals, 1997.
6 International Conference on Harmonization (ICH), Technical Requirements for Registration of
Pharmaceuticals for Human Use, ICH Harmonized Tripartite Guideline, S1B: Testing for Carcinogenicity of
Pharmaceuticals, 1997.
7 ICH, Technical Requirements for Registration of Pharmaceuticals for Human Use, ICH Harmonized Tripartite
Guideline, S1C(R): Addendum: Addition of a Limit Dose and Related Notes, 1997.
8 ICH, Technical Requirements for Registration of Pharmaceuticals for Human Use, ICH Harmonized Tripartite
Guideline, S1C: Dose Selection for Carcinogenicity Studies of Pharmaceuticals, 1994.
9 National Research Council (NRC)/National Academy of Sciences (NAS), Issues in Risk Assessment, National
Academy Press, pp.15-19&43-96, 1993.
10 International Life Sciences Institute (ILSI)/Health and Environmental Sciences Institute (HESI)), Committee
on Carcinogenicity of Chemicals in Food, Consumer Products and Environment, Statement on ILSI/ HESI
Research Programme on Alternative Cancer Models (Letter to the Editor), Toxicologic Pathology, 31(2):254-
257, 2003.
11 NRC/NAS, Institute of Laboratory Animal Resources, Guide for the Care and Use of Laboratory Animals,
National Academy Press, Washington, D.C., 1996.
12 Scientific Advisory Committee on Alternative Toxicological Methods (SACATM) of the Interagency
Coordinating Committee on the Validation of Alternative Methods, Summary Minutes for March 10 - 11
Meeting, Bethesda, Maryland, 2004.
13 NRC/NAS, Subcommittee on Laboratory Animal Nutrition, Committee on Animal Nutrition, Board on
Agriculture, Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, National Academy Press,
Washington, D.C., 1995.
14 Keenan K.P., J.B. Coleman, C.L. McCoy, C.M. Hoe, K.A. Soper and P. Laroque, Chronic Nephropathy in ad
libitum Overfed Sprague-Dawley Rats and its Early Attenuation by Increasing Degrees of Dietary (Caloric)
Restriction to Control Growth, Toxicologic Pathology, 26(6):788-798, 2000.
15 Rao G.N. and P.W. Crockett, Effect of Diet and Housing on Growth, Body Weight, Survival and Tumor
Incidences of B6C3F1 Mice in Chronic Studies, Toxicologic Pathology, 31(2):243-250, 2003.
16 Clinton S.K., A.L. Mulloy, S.P. Li, H.J. Mangian and W.J. Visek, Dietary Fat and Protein Intake Differ in
Modulation of Prostate Tumor Growth, Prolactin Secretion and Metabolism, and Prostate Gland Prolactin
Binding Capacity in Rats, The Journal of Nutrition, 127:225-237, 1997.
17 NTP/DHHS, Board of Scientific Counselors, Report of the NTP Ad Hoc Panel on Chemical Carcinogenesis
E. Histopathology of Lymphoid Organs
VII. References
Redbook 2000: IV.C.6 Carcinogenicity Studies with Rodents
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
Testing and Evaluation, 1984.
18 Office of Science and Technology Policy/Executive Office of the President, Chemical Carcinogens; A Review
of the Science and its Associated Principles. The Federal Register 15(50):10372-10442, March 14, 1985.
19 McConnell, E.E., The Maximum Tolerated Dose: the Debate. Journal of the American College of Toxicology,
8(6):1115-1120, 1989.
20 FDA/DHHS, Draft Guidance for Industry on Computerized Systems Used in Clinical Trials; Availability, The
Federal Register, 69(191):59239-59240, October 4, 2004.
21 Gaylor D.W., R.L. Suber, G.L. Wolff and J.A Crowell, Statistical Variation of Selected Clinical Pathological
and Biochemical Measurements in Rodents, Proceedings of the Society for Experimental Biology and Medicine,
185:361-367, 1987.
22 Ragan H.A. and R.E. Weller, Markers of Renal Function and Injury, In: The Clinical Chemistry of Laboratory
Animals, Second Edition, Taylor&Francis, Philadelphia, PA, pp. 520-533, 1999.
23 Society of Toxicologic Pathology (STP) Immunotoxicology Working Group (P. HALEY et al.), STP Position
Paper: Best Practice Guideline for the Routine Pathology Evaluation of the Immune System, Toxicologic
Pathology, 33:404-407, 2005.
24 Keenan K.P., C.M. Hoe, L Mixson, C.L. McCoy, J.B. Coleman, B.A. Mattson, G.A. Ballam, L.A. Gumprecht,
and K.A. Soper, Diabesity: A Polygenic Model of Dietary-Induced Obesity from ad libitum Overfeeding of
Sprague-Dawley Rats and its Modulation by Moderate and Marked Dietary Restriction, Toxicologic Pathology,
33:650-674, 2005.
Links on this page:
Redbook 2000: IV.C.6 Carcinogenicity Studies with Rodents
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078349.htm
3. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078388.htm
July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
This section of Redbook 2000 supersedes the 1993 "draft" Redbook Chapter IV.C.7. The FDA acknowledges
that it is complicated and difficult to conduct a combined chronic toxicity/carcinogenicity rodent study
particularly with an in-utero exposure phase. This is often due to difficulty in setting and administering
appropriate dose levels for both types of studies concurrently. Additionally, the general objectives of these two
types of studies are different. Nevertheless, when pre-chronic studies provide reasonable estimates of toxicity
to predict the information (i.e., treatment doses) to be used in a single bioassay, a chronic toxicity study may
be combined with a carcinogenicity study and reveal information about an ingredient's potential to be a
carcinogen as well as the maximum dose that produces no adverse effects.
The FDA recommends that the petitioner/notifier consult with the FDA before conducting a combined study.
Sponsors/submitters of petitions/notifications are also encouraged to become familiar with the Guidance for
Chronic Toxicity Studies with Rodents (Chapter IV.C.5.a. 2
), Carcinogenicity Studies with Rodents (Chapter
IV.C.6. 3 ), In-Utero Exposure Phase for Addition to Carcinogenicity Studies or Chronic Toxicity Studies with
Rodents (Chapter IV.C.8. 4 ), Reporting Results of Toxicity Studies (Chapter IV.B.2. 5
), Pathology
Considerations in Toxicity Studies (Chapter IV.B.3. 6
), and Statistical Considerations in Toxicity Studies
(Chapter IV.B.4. 7 ) during the development of study design.
Redbook 2000: IV.C.7 Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.7. Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
Links on this page:
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.7 Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
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4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078394.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078409.htm
6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078318.htm
7. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
Redbook 2000: IV.C.7 Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
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July 2007
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration’s (FDA’s) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
I. 	Good Laboratory Practice
II. 	Test Animals
III. 	Test Substance
IV. 	Experimental Design
V. 	Observations and Clinical Tests
VI. 	Necropsy and Microscopic Examination
VII. 	References
Scientifically justified changes to 1993 "draft" Redbook version of this section have been made after consulting
with other authoritative guidelines [3] [4] [5] [10] [11] [12] [19] [20] [22] [23] and publications (see the relevant
sections below).
The FDA recommends including an in-utero exposure phase in a carcinogenicity or a chronic toxicity study
conducted with rodents for the safety assessment of potential food ingredients with the highest levels of
concern (e.g., Concern Level III direct food additives 2
, food contact substances 3 with cumulative exposure at
or greater than 1 ppm). The animal toxicity studies recommended in this chapter are designed to determine
whether a test food ingredient has early developmental effects that may increase the incidence of cancers
and/or chronic disease outcomes (e.g., altered glucose tolerance, diabetes mellitus, cardiovascular disorders)
when administered in regularly repeated oral doses for the duration of the study in the test animals.
An in-utero exposure phase should be added to one of the two recommended rodent carcinogenicity studies
(or bioassays; see Chapter IV.C.6 4
.). In general, the in-utero phase should be added to a bioassay study with
rats since the rat is the recommended species for reproduction studies (see Chapter IV.C.9.a 5
.) and the FDA
has a larger database on carcinogenicity bioassays with in-utero exposure in rats than in mice. When chronic
toxicity studies are the only long-term studies in support of the safety of a food ingredient, the FDA
recommends on a case-by-case basis that an in-utero exposure phase be added to at least one of the studies.
The purpose of this chapter is to provide specific guidance for the design and conduct of an in-utero exposure
phase addition to bioassay or chronic toxicity studies of food ingredients. However, these general procedures
Redbook 2000: IV.C.8 In-Utero Exposure Phase for Addition to Carcinogenicity Studies
or Chronic Toxicity Studies with Rodents
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.8. In-Utero Exposure Phase for Addition to Carcinogenicity Studies or
Chronic Toxicity Studies with Rodents
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
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may also be applied to a combined chronic toxicity/carcinogenicity study or shorter-term toxicity studies with
modifications (e.g., duration, dose, etc). The FDA encourages petitioners and/or notifiers to consult with the
appropriate FDA scientists before toxicity testing has begun if they have questions about the appropriateness
of adding an in-utero exposure phase to any of these studies. Sponsors/submitters of petitions/notifications
are encouraged to also become familiar with the Guidelines for Reporting Results of Toxicity Studies (Chapter
IV.B.2 6
.), Pathology Considerations in Toxicity Studies (Chapter IV.B.3 7 .), Statistical Considerations in
Toxicity Studies (Chapter IV.B.4 8 .), during the development of study design.
Nonclinical laboratory studies discussed in this chapter should be conducted according to U.S. FDA good
laboratory practice (GLP) regulations, issued under Part 58 of Title 21 9 of the Code of Federal Regulations.
This document may be obtained from the Superintendent of Documents, U.S. Government Printing Office,
Washington, D.C., 20402, (toll free 866-512-1800 or DC area 202-512-1800). Studies performed under other
international/national guidelines may be considered equivalent to those conducted under U.S. FDA GLP
regulations. Specific area(s) of non-compliance with FDA GLP regulations should be discussed and justified.
Recommendations about the care, maintenance, and housing of animals contained in the National Research
Council, Guide for the Care and Use of Laboratory Animals [24] should be followed unless they conflict with
specific recommendations in this chapter.
Guidance contained within this chapter is for studies with mice and rats; if other rodent species are used,
modifications may be necessary. Both male and female test animals, which are healthy and have not been
subjected to previous experimental procedures, should be used.
It is important to consider the test animals' general sensitivity and the responsiveness of particular organs and
tissues of test animals to toxic chemicals when selecting rodent species, strains, and substrains for toxicity
studies. The selection of inbred, out-bred, or hybrid rodent strains for toxicity tests should be based upon the
scientific questions to be answered. Strains selected should not have low fecundity and should be sensitive to
teratogens and embryotoxins. Additionally, it is important that test animals come from well-characterized and
healthy colonies. Because recent information suggests survivability problems exist for some strains of rats,
test animals should be selected that are likely to survive for the recommended duration of the study (see
discussions under sections II.D: Number and Sex and IV.A: Duration of Testing). The FDA encourages
petitioners/notifiers to consult with the appropriate FDA scientists before toxicity testing has begun if they
have questions about the appropriateness of a particular species, strain, or substrain.
Another Center within the FDA (Center for Drug Evaluation and Research), as part of a pilot program, accepts
safety data from six month studies employing genetically modified mice (i.e., transgenic mice) as a
replacement for one of the rodent carcinogenicity studies.[20] The Office of Food Additive Safety will consider
this type of information only as supplemental data but does not consider such studies to be substitutes for the
two (2-year) rodent carcinogenicity bioassays. Data from transgenic rodent carcinogenesis or mutagenesis
assays may be useful in evaluating compound-specific questions relating to mechanism of action or tissue
distribution. For the determination of carcinogenic risk of certain kinds of test substances (i.e., constituents
and/or contaminants in food ingredients), the transgenic mouse model is inappropriate in that it does not
provide quantitative dose-response data. It also has not, as of this date, been fully validated or accepted by
most national and international validation organizations (e.g., Scientific Advisory Committee on Alternative
Toxicological Method of the Interagency Coordinating Committee on the Validation of Alternative Methods [16] )
or testing laboratories. At this time, there is no large repository of historical control data to establish baseline
parameters. Given the nature of consumption patterns of food ingredients (i.e., chronic, lifetime exposures),
it is important to provide the chronic safety testing of food ingredients that would be representative of lifetime
exposure in humans, in addition to also providing that only quantitative data derived from fully validated test
systems be used in their safety assessment.
Following a suitable acclimation period of at least 5 days, parental animals should receive the test substance.
Females should receive the test substance for a minimum of four weeks prior to mating and males should
receive the test substance for at least ten weeks prior to exposure to cover the full spermatogenic cycle.
I. Good Laboratory Practice
II. Test Animals
A. Care, Maintenance and Housing:
B. Selection of Species and Strains:
C. Age (start of dosing):
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Dosing of all test and control pups (F1) should begin at weaning (see also section IV.A: Duration of testing).
Experimental and control groups should have a sufficient number of animals at the beginning of the study to
ensure that at least 25 rodents per sex per group survive to the end of the study. Having sufficient animals
survive to the end of the study allows for objective assessment of test substance-related effects including
tumor development. Survival can be improved by reducing non-compound related animal pathology, which
may occur as a result of excessive weight gain (e.g., obesity-related pituitary changes), or as sequelae to
other stressors (e.g., parasitic infection).
The FDA recommends that petitioners/notifiers carefully consider their choice of rat strains for bioassays or
chronic toxicity studies, since some strains have more serious problems with survivorship than other strains.
It is recommended that these studies begin with at least 70 animals per sex per group. Petitioners and/or
notifiers should begin bioassays with more than 70 animals per sex per group if survivorship is expected to be
a problem with the rat strain used in the study. If fewer than 25 animals per sex per group are expected to
survive to the end of the study (e.g., 1-year or longer in chronic study and 2-years in bioassay, see section
IV.A: Duration of Testing), petitioners/notifiers should take particular care to ensure and document early
detection of dead animals through attentive and frequent cage-side observations, thus minimizing the loss of
tissues from autolysis. In addition, they should consult with the FDA as soon as a problem with survivorship
in a carcinogenicity or chronic study becomes apparent.
One male and one female per litter are preferred; no more than two males and two females per litter should
be included in any group. For example, if the petitioner decides that each group should contain 70 animals
per sex, at least 70 litters/group should be produced in the in-utero phase. Thus, for this example the
number of parental animals per sex for the in-utero phase should be sufficient to ensure at least 70 litters per
group.
If interim necropsies are planned, the total number of rodents of each sex per group should be increased by
the number scheduled to be sacrificed before completion of the study. A minimum of 10 rodents per sex per
group should be available for each interim necropsy.
For each mating, a female should be placed with a single randomly selected male from the same dose group
until pregnancy occurs or two to three weeks have elapsed. Animals should be separated as soon as possible
after evidence of copulation has been observed. If mating has not occurred after two to three weeks, the
animals should be separated without further opportunity for mating. Mating pairs should be clearly identified
in the data. Sibling matings should be avoided. 	Each morning, all females should be examined for the
presence of sperm in the vaginal lavage or the presence of a vaginal plug; if sperm and/or a vaginal plug are
found, this is considered day zero of gestation. Near parturition, pregnant females should be caged separately
in delivery or maternity cages that contain nesting materials. Pregnant females in test and control groups
should be allowed to litter naturally.
Standardization of the number of pups per litter through culling is optional. Litters may be standardized to 10
or 8 based on historical litter size for the strain. It is recommended that standardization be performed on
postnatal day 4 by reducing all litters of more than 10 to 10 (or more than 8 to 8) in a random manner. If
possible, the retained litter-mates should consist of equal numbers of males and females; excess males or
females should be randomly selected out. Random selection is important to guard against the human
tendency to keep the fit animals in the study.
One animal per sex per litter, or up to two animals for single sex litters, should be randomly selected.
Generally, it is not possible to treat animals for infection during the course of a study without the possibility of
interaction between the therapeutic agent used for treatment and the test substance. This interaction may
seriously confound or complicate the interpretation of study results. However, if problems with infection do
occur, the sponsor for the study should use their best judgment in proceeding with the study and inform the
FDA of their decision. In addition, the FDA requests that they provide a full and detailed description of the
D. Number and Sex:
E. Mating Procedures:
F. Standardizing the Number of Pups per Litter:
G. Selection of Pups (F1):
H. Infected Animals:
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justification for study continuation and possible implications of the infection, and if applicable, the justification
and possible implications for treatment of the infection.
Test animals should be characterized by reference to their species, strain (and substrain), sex, age, and
weight. Each animal should be assigned a unique identification number (e.g., ear tag, implanted identification
chip, tattoo).
Animals should be single-caged during the study, except during mating and lactation. This recommendation
reflects three points of consideration:
z The amount of feed consumed by each animal in the study cannot be determined with sufficient
accuracy when more than one animal is housed in each cage. This information is necessary in
the determination of feed efficiency (relationship of feed consumed to body weight gained).
z Minimizing the possibility of confounding analyses in determining whether decreases in body
weight gain are due to decreased palatability or test substance mediated toxicity.
z Organs and tissues from moribund and dead animals which are single-caged would not be lost
due to cannibalism.
In general, feed and water should be provided ad libitum, and the diets should meet the nutritional
requirements to support pregnancy in the test species as well as of the species for normal growth and
longevity. [25] Unless special circumstances apply which justify otherwise, care should be taken to ensure that
the diets of the test substance treated groups of animals contain the same levels of calories and nutrients
(e.g., fiber, micronutrients) as the diets of the control group. Inadequately controlled dietary variables may
result in nutritional imbalances or caloric deprivation that could confound interpretation of the toxicity study
results (e.g., lifespan, background rates of tumor incidences) and alter the outcome and reproducibility of the
studies. However, the FDA is also aware of some beneficial effects on the survivability of certain animal
species that have been on calorie-restricted, [7] [8] or low-protein diets. [1] [15] The FDA may accept such
study results if the sponsor provides sufficient historical control data on the diet, and the study is well-
conducted.
The following issues are important to consider when establishing diets for animals in toxicity studies:
When the test substance has no caloric value and constitutes a substantial amount of the diet (e.g., more
than 5%), both caloric and nutrient densities of the high dose diet would be diluted in comparison to the diets
of the other groups. As a consequence, some high dose animals may receive higher test substance doses than
expected because animals fed such diluted diets ad libitum may eat more than animals in other dosed groups
to compensate for the differences in energy and nutrient content of the high dose diets. Such circumstances
make it especially important that feed consumption of these animals be as accurately and closely monitored
as possible in order to determine whether changes observed could be due to overt toxicity of the test
substance or to a dietary imbalance. To further aid in this assessment, two control groups can be used; one
group would be fed the undiluted control diet and a second group would be fed the control diet supplemented
with an inert filler (e.g., methylcellulose) at a percentage equal to the highest percentage of the test
substance in the diet.
When the vehicle for the test substance is expected to have caloric and/or nutritional values, which are
greater than that of the control ration, an adjustment in the caloric and/or nutritional components may be
necessary.
When administration of the test substance is expected to have an effect on feed intake because of its
unpleasant taste or texture, other feeding regimens or experimental designs may be necessary. Consultation
with the FDA is recommended when alternatives are being considered.
When the test substance interferes with the absorption of nutrients, leading to nutritional deficiencies or
changes in nutrient ratios, this can confound assessment of the toxicological endpoints under consideration.
For example, fat soluble vitamins may preferentially partition with a mineral oil or fat substitute which is
largely unabsorbed, such that a potential deficiency in these vitamins may result. This potential may be
eliminated by additional nutrient fortification of the feed for those groups receiving the test substance.
I. Animal Identification:
J. Caging:
K. Diet:
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Appropriate levels of nutrient fortification should be determined experimentally.
Other related issues (e.g., advantages and disadvantages of using natural ingredient versus purified diets) are
discussed in the National Research Council publication on nutrient requirements of laboratory animals.[25]
Animals should be assigned to control and compound treated groups in a stratified random manner. This will
help minimize bias and assure comparability of pertinent variables across compound treated and control
groups. In general, mean body weights and/or body weight ranges are used as a basis of randomization. If
other characteristics are used as the basis for randomization, they should be described and justified.
Animals in all groups should be placed on study on the same day. If this is not possible because of the large
number of animals in a study, animals may be placed on study over several days. When the latter
recommendation is followed, a preselected portion of the control and experimental animals should be placed
on the study each day in order to maintain concurrence.
Excessive mortality due to poor animal management is unacceptable and may be a cause to repeat the study.
Adequate animal husbandry practices should result in considerably less than 10 % loss of animals and tissues
or organs in a study because of autolysis. Autolysis in excess of this standard may be a cause to repeat the
study.
Necropsy should be performed soon after an animal is sacrificed or found dead, so that loss of tissues due to
autolysis is minimized. When necropsy cannot be performed immediately, the animal should be refrigerated at
a temperature that is low enough to prevent autolysis (i.e., between 4o
C and 8 o
C), but not so low as to cause
cell damage. If histopathological examination is to be conducted, tissue specimens should be taken from the
animals and placed in appropriate fixatives when the necropsy is performed.
The test substance used in carcinogenicity or chronic toxicity studies with an in-utero exposure phase should
be the same substance that the petitioner/notifier intends to market or, when appropriate, the test substance
may be a constituent chemical or an impurity. A single lot of test substance should be used throughout the
study. When this is not possible, lots that are as similar as possible in purity and composition should be used.
It is the responsibility of the petitioner/notifier to notify the animal test facility of the purity of the test
substance, as well as the identity and concentration of any impurities that might be present.
The identity of the test substance (e.g., either a single component or a mixture of components) should be
known. The petitioners/notifiers are encouraged to consult with the FDA regarding the method(s) of
determination of the test compound, and should provide all relevant Chemical Abstract Service (CAS) Registry
numbers.
The composition of the test substance should be known including the name and quantities of all major
components, known contaminants and impurities, and the percentage of unidentifiable materials.
The test samples should be stored under conditions that maintain their stability and purity until the studies
are complete.
The expiration date of the test material should be known and easily available. Test materials should not be
used past their expiration date.
L. Assignment of Control and Compound Treated Animals:
M. Mortality:
N. Autolysis:
O. Necropsy:
III. Test Substance
A. Identity:
B. Composition/Purity:
C. Conditions of Storage:
D. Expiration Date:
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The parental animals should receive the test substance starting at a minimum four weeks (or ten weeks
exposure is preferable for males to cover full spermatogenic cycle) prior to mating. Exposure should be
continued throughout pre-mating, mating, gestation, and lactation until the F1 animals have been weaned.
Dosing of all test and control F1 animals should begin at weaning, and continue for 7 days per week for the
duration of the study (e.g., 1-year or longer in chronic study and 2-years in bioassay).
In general, the FDA does not recommend early termination of carcinogenicity studies due to decreased
survivorship (see discussions under section II.D: Number and Sex). Carcinogenicity bioassays should be
conducted for a major portion of the test animal's lifetime. While it is desirable to have an optimum number
of animals survive to the end of the study, the FDA believes there is more benefit, as well as added sensitivity,
to be gained by conducting carcinogenicity bioassays for as long as possible, or for no longer than the full 24
months that is recommended in this guidance.
The route of administration of the test substance should approximate that of normal human exposure, and if
possible, the oral route should be used. A justification should be provided when using other routes. The same
method of administration should be used for all test animals throughout the study. The test substance should
be administered in one of the following ways:
z In the diet, if human exposure to the test substance is likely to be through consumption of solid
foods or a combination of solid and liquid foods. If the test substance is added to the diet,
animals should not be able to selectively consume either basal diet or test substance in the diet
on the basis of color, smell, or particle size. If the test substance is mixed with ground feed and
pelleted, nothing in the pelleting process should affect the test substance (for example, heat-
labile substances may be destroyed during pellet production by a steam process). When the test
substance is administered in the diet, dietary levels should be expressed as mg of the test
substance per kg of feed.
z Dissolved in the drinking water, if the test substance is likely to be ingested in liquid form by
humans (for example, in soft drinks or beer), or if administration in the diet of rodents is
inappropriate. The amount of test substance administered in drinking water should be expressed
as mg of test substance per ml of water.
z By encapsulation or oral intubation (gavage) , if the two previous methods are
unsatisfactory or if human exposure is expected to be through daily ingestion of a single, large
bolus dose instead of continual ingestion of small doses. If the test substance is administered by
gavage, it should be given at approximately the same time each day. The maximum volume of
solution that can be given by gavage in one dose depends on the test animal's size; for rodents,
the volume ordinarily should not exceed 1 ml/100 g body-weight. If the gavage vehicle is oil,
then the volume should be no more than 0.4 ml/100 g of body weight, and the use of a low-fat
diet should be considered. It is best to adjust the volume every 1-3 days based on the animal’s
body weight response. If the test substance should be given in divided doses, all doses should be
administered within a 6 hour period. Doses of test substance administered by gavage should be
expressed as mg of test substance per ml of gavage vehicle. Finally, the petitioner/notifier
should provide information that can allow the FDA to conclude that administration of the test
substance by encapsulation or gavage is equivalent in toxicologically important respects to
administration in the diet or drinking water. Alternatively, metabolic information on both modes
of administration should be provided so that appropriate interpretation of data can be
accomplished.
A concurrent control group of test animals fed the basal diet is necessary for all studies. A carrier or vehicle
for the test substance should be given to control animals at a volume equal to the maximum volume of carrier
IV. Experimental Design
A. Duration of Testing:
B. Route of Administration:
C. Dose Groups:
1. Controls:
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or vehicle given to any dosed group of animals. Sufficient toxicological information should be available on the
carrier or vehicle to ensure that its use will not compromise the results of the study. If there is insufficient
information about the toxic properties of the carrier or vehicle used to administer the test substance, an
additional control group that is not exposed to the carrier or vehicle should be included. In all other respects,
animals in the control group should be treated the same as animals in dosed groups. (See also section II.K:
Diet.)
It is recommended that a minimum of three dose levels of the test substance be used in carcinogenicity
bioassays with an in-utero exposure phase. As a result of maternal or fetal toxicity, it may be necessary to
use lower doses during the in-utero phase of the studies in order to produce sufficient offspring for the post-
weaning phase. Data justifying this protocol modification should be provided; it is recommended that pilot
studies be performed to select doses. Results from metabolism and pharmacokinetic studies should also
provide guidance in selecting an appropriate dosage regimen.
When designing and conducting carcinogenicity bioassays with an in-utero exposure phase the following
should be considered: 1) the high dose (maximum tolerated dose) should be sufficiently high to induce toxic
responses in test animals, and should not cause fatalities high enough to prevent meaningful evaluation of the
data from the study; 2) the low dose should not induce toxic responses in test animals; and 3) the
intermediate dose(s) should be sufficiently high to elicit minimal toxic effects in test animals (such as
alterations in enzyme levels or slight decreases in body weight gains. Administration of the test substance to
all dose groups should be done concurrently (see discussions under section II.L: Assignment of Control and
Compound Treated Animals).
High Dose: The high dose should be the maximum tolerated dose (MTD).
It is not acceptable to select doses for carcinogenicity bioassays with an in-utero exposure phase based on
information unrelated to the toxicity of the test substance. For example, the highest dose should not be
selected so as to provide a pre-determined margin of safety over the maximum expected human exposure to
the test substance, assuming that the results of testing at that dose will be negative.
This guidance recommends that the highest dose in carcinogenicity bioassays with an in-utero exposure phase
should be the MTD. FDA scientists will consider the question of whether the substance was tested at the MTD
as one of several factors that may affect interpretation of the results of the bioassays. The bioassays should
include a description of the process used to select the MTD for the study.
The MTD is defined by the National Toxicology Program (NTP) as "that dose which, when given for the
duration of the chronic study as the highest dose, will not shorten the treated animals' longevity from any
toxic effects other than the induction of neoplasms".[21] The Office of Science and Technology Policy provides
the following advice, "The highest dose should be selected after an adequate prechronic study and after
evaluating other relevant information, as necessary, to determine the highest dose consistent with predicted
minimal target organ toxicity and normal life span, except as a consequence for the possible induction of
cancer.". [13] In addition, the NTP cautions that the MTD should not cause morphologic evidence of toxicity of
a severity that would interfere with the interpretation of the study results. [21]
In general, the MTD is estimated following a careful analysis of data from appropriate subchronic toxicity
tests. As the scientific community's experience with toxicity testing has accumulated, the need to consider a
broad range of biological information when selecting the MTD has become increasingly clear. For example,
data concerning changes in body and organ weight and clinically significant alterations in neurological,
hematological, urinary and clinical chemistry measurements, in combination with more definitive toxic, gross
or histopathologic endpoints, can be used to estimate the MTD.
Although the high dose in a carcinogenicity study with an in-utero exposure phase should be selected to
achieve the MTD, the FDA recognizes that this goal may not always be met. There are uncertainties in
predicting the MTD for long-term bioassays from the results of shorter-term studies. Because working
definitions of the MTD require the use of scientific judgment, it is sometimes possible for competent
investigators looking at the same set of data to arrive at significantly different estimates of the MTD. Such
disagreement may be based on different interpretations of the results of metabolic studies or different
conclusions about whether an organ alteration is adaptive or toxicological. In situations such as these, when
it is unclear what dose of the test substance is the MTD, the petitioner/notifier should consult with the FDA to
determine an appropriate high dose (MTD) for the carcinogenicity bioassay with an in-utero exposure phase.
The FDA recognizes that use of the MTD in carcinogenicity bioassays with an in-utero exposure phase has
several advantages; these include:
2. Selection of Treatment Doses for Carcinogenicity Studies with an in-utero exposure phase:
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z Compensating for the inherent lack of sensitivity of the bioassay, including the relatively small
number of rodents used in the study;
z Providing consistency with other models used in toxicology (e.g., high enough doses should be
used in order to elicit evidence of the presumed toxicity or increase probability of detecting rare
tumors and identifying weak carcinogens); and
z Permitting comparison of carcinogenic potencies of substances tested at the MTD, even when the
data are collected from different studies. [9]
The FDA acknowledges that its recommendation to conduct carcinogenicity studies with an in-utero exposure
phase at the MTD may result in the use of doses that are so high as to be unrepresentative of the toxicity of
the test substance at lower doses in animals or humans. For example, excessively high doses of a test
substance can saturate enzyme systems involved in detoxification of the test substance. Given the above,
after thorough internal assessment and in an agreement with other authoritative bodies,[6] [26] the FDA
concludes that the MTD is still the best choice for selecting the high dose for carcinogenicity studies even with
an in-utero exposure phase. It should be noted that this is also in line with the principles discussed by the
International Conference on Harmonization which recommends the use of the MTD in choosing the high dose
for drug safety testing.[4] [5]
Low Dose:
The low dose level should not interfere with the normal growth, development, and lifespan of test animals, nor
should it produce any signs of toxicity.
Intermediate Dose:
The intermediate dose should produce minimal signs of toxicity. The exact dose selected as the intermediate
dose may depend on the pharmacokinetic properties of the test substance.
Optional Fourth Dose Level:
If significant differences exist in the pharmacokinetic or metabolic profiles of the test substance administered
at high and low doses, an optional (fourth) dose level may be included in the study. This dose level should be
the highest dose that produces a pharmacokinetic or metabolic profile similar to profiles obtained at lower
doses. The number of test animals in the optional group should be selected to provide approximately the
same sensitivity for the detection of the carcinogenic effects of the test substance as the higher dose group
provides.
It is recommended that a minimum of three dose levels of the test substance be used in chronic toxicity
studies with an in-utero exposure phase. Dose selection should be based on results from subchronic studies
and other related test substance information (i.e., metabolism and pharmacokinetic studies). As a result of
maternal or fetal toxicity, it may be necessary to use lower doses during the in-utero phase of the chronic-
feeding studies in order to produce sufficient offspring for the post-weaning phase. Data justifying this
protocol modification should be provided.
The FDA acknowledges that it is complicated and difficult to conduct a combined chronic
toxicity/carcinogenicity rodent study with an in-utero exposure phase due to difficulty in setting and
administering appropriate dose levels for both types of studies concurrently. However, when pre-chronic
studies provide reasonable estimates of toxicity to predict the information on treatment doses to be used in a
single bioassay, a chronic toxicity study may be combined with a carcinogenicity study with an in-utero
exposure. It is recommended that the petitioner/notifier consult with the FDA before conducting a combined
study.
The following is a general consideration in selecting the treatment dose levels for chronic toxicity studies with
an in-utero exposure phase: 1) the high dose should be sufficiently high to induce toxic responses in test
animals, and should not cause fatalities high enough to prevent meaningful evaluation of the data from the
study; 2) the low dose should not induce biologically significant toxic responses in test animals; and 3) the
intermediate dose should be sufficiently high to elicit minimal toxic effects in test animals (such as alterations
in enzyme levels or slight decreases in body weight gains).
High Dose:
The high dose in a chronic toxicity study should produce toxicity so that a toxicological profile of the test
substance can be obtained. We do not recommend that petitioner/notifiers use information unrelated to the
toxicity of the test substance as a basis for dose selection. For example, the highest dose should not be
3. Selection of Treatment Doses for Chronic Toxicity Studies with an in-utero exposure phase:
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selected so as to provide a pre-determined margin of safety over the maximum expected human exposure to
the test substance, assuming that the results of testing at that dose will be negative. When no toxicity is
observed in other studies, however, the high dose could be subject to some preset limits such as the highest
percent of the test substance in the diet that could be fed without compromising nutritional balance with other
nutrients (e.g., about 5%, see also ‘section II.H: Diet’ for other important dietary issues).
In general, the high dose tested is estimated following a careful analysis of data from appropriate subchronic
toxicity tests. As the scientific community's experience with toxicity testing has accumulated, the need to
consider a broad range of biological information when selecting the high dose has become increasingly clear.
For example, data from a subchronic (90-day) study concerning changes in body and organ weight and
clinically significant alterations in neurological, hematological, urinary and clinical chemistry measurements, in
combination with more definitive exposure-related toxic, gross or histopathologic endpoints, can be used to
estimate the high dose in a chronic toxicity study.
Although the high dose in a chronic toxicity study should be selected to achieve toxic responses in test
animals, and should not cause fatalities high enough to prevent meaningful evaluation of the data from the
study, the Agency recognizes that this goal may not always be met. In situations such as these, when it is
unclear what dose of the test substance is the high dose, the petitioner/notifier should consult with the Agency
to determine an appropriate high dose for the chronic toxicity study.
Low Dose:
The low dose level should not interfere with the normal growth, development, and lifespan of test animals, nor
should it produce any other biologically significant signs of toxicity (e.g., NOEL or NOAEL).
Intermediate Dose:
The intermediate dose should produce minimal signs of toxicity. The exact dose selected as the intermediate
dose may depend on the pharmacokinetic properties of the test substance.
Computerized systems that are used in the generation, measurement, or assessment of data should be
developed, validated, operated, and maintained in ways that are consistent with the intention of the Good
Laboratory Practice principles. [18] The FDA has endorsed the use of the Standard for Exchange of Nonclinical
Data (SEND) format for electronic transmission of animal study data. You are encouraged to contact the FDA
for more information on this electronic protocol.
Routine cage-side observations of all parental animals should be made for general signs of departure from
normal activity, morbidity and mortality once or twice a day until F1 animals are weaned. The usual interval
between multiple periods of observations should be at least 6 hours. Individual records should be maintained
for each animal and, as possible, the onset and progression of any effects should be recorded, preferably
using a scoring system. If grossly visible or palpable tumors develop, the following parameters should be
recorded; time of onset, location, dimensions, appearance and progression.
In a chronic toxicity (or combined chronic/carcinogenicity) study with an in-utero exposure phase, an
expanded set of clinical evaluations should be carried out on animals inside and outside of the cage to enable
detection not only of general signs of departure from normal activity, morbidity and mortality but also of
neurologic disorders, behavioral changes, autonomic dysfunctions, and other signs of nervous system
toxicity. This expanded set of clinical examinations, conducted on animals inside and outside the cage, should
be performed on all animals at least once prior to initiation of treatment, and periodically during treatment.
Specific information on this type of evaluation is contained in Chapter IV.C.10 10 . (see also the section
below).
If reproductive parameters (e.g., fertility index, gestation length, gestation index, live-born index, etc) are
collected, they should be included in the study report.
These animals should be observed carefully for signs of departure from normal activity, morbidity and
mortality at least twice daily throughout the study period. The usual interval between multiple periods of
observations should be at least 6 hours. Observations of general appearance and the presence of dead pups
should be recorded. The total number of pups per litter and the number of pups per sex should be recorded.
D. Computerized systems
V. Observations and Clinical Tests
A. Observations of Parental Animals:
B. Observations of F1 Animals:
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Individual records should be maintained for each animal and, as possible, the onset and progression of any
effects should be recorded, preferably using a scoring system. If grossly visible or palpable tumors develop,
the following parameters should be recorded; time of onset, location, dimensions, appearance and
progression.
In a chronic toxicity (or combined chronic/carcinogenicity) study with an in-utero exposure phase, an
expanded set of clinical evaluations should be carried out on animals inside and outside of the cage to enable
detection not only of general signs of departure from normal activity, morbidity and mortality but also of
neurologic disorders, behavioral changes, autonomic dysfunctions, and other signs of nervous system
toxicity. Specific information about the systematic clinical tests/observations is contained in Chapter
IV.C.10 11 . This expanded set of clinical examinations, conducted on animals inside and outside the cage,
should be age appropriate and performed on all animals periodically during treatment. Signs noted should
include, but not be limited to, changes in skin, fur, eyes, mucous membranes, occurrence of secretions and
excretions or other evidence of autonomic activity (e.g., lacrimation, piloerection, pupil size, unusual
respiratory pattern). Additionally, changes in gait, posture and response to handling, as well as the presence
of clonic or tonic seizures, stereotypic (e.g., excessive grooming, repetitive circling) or bizarre behavior (e.g.,
self-mutilating, walking backwards) should be recorded. During the course of a study, toxic and
pharmacologic signs may suggest the need for additional clinical tests or expanded post-mortem
examinations.
Accurate individual body weight, feed, and water consumption measurements are critical in the objective
evaluation of the effect of a test substance on experimental animals, since changes in these variables are
often the first signs of toxicity. Complete records for these parameters are essential in assessing the time-
related occurrence of toxicity-induced changes. When these data are not carefully recorded the evaluation of
the overall cancer-inducing potential for a test substance may be compromised. A discussion of some of the
variables that affect feed consumption and weight gain/loss can be found under sections II.K: Diet and IV.B:
Route of Administration.
Parental animals should be weighed immediately before the first dose of the test substance is administered,
and weekly throughout gestation and lactation. If the substance is given by gavage, animals should be
weighed every 1-3 days. Feed consumption should be measured weekly. Water consumption should be
measured weekly if the test substance is administered in the water.
Body weights for all F1 animals should be recorded weekly for the first 13 weeks after weaning, and monthly
thereafter for the duration of the study. Feed consumption (or water consumption if the test substance is
administered in the drinking water) should be measured at the same interval as body weights.
Petitioners/notifiers should also attempt to quantify spillage of feed by experimental animals. When it is
suspected that test compound administration may be affected by any of the following conditions; 1) feed
palatability issues, 2) marked changes in body weight, or 3) increased numbers of animal deaths, the
petitioners/notifiers should measure weights and feed (water) consumption more frequently after the initial 13
week period (e.g., every two weeks). Petitioners/notifiers should also use this accumulated information to
calculate intake of the test substance as mg/kg body weight/day.
Ophthalmological examination, hematology profiles, clinical chemistry tests, and urinalyses should be
performed in all F1 animals as described in the following sections:
This examination should be performed by a qualified individual on all F1 animals during the first 2 weeks of
study and on control and high-dose animals at the end of the study. If the results of examinations at
termination indicate that changes in the eyes may be associated with administration of the test substance,
ophthalmological examinations should be performed on all F1 animals in the study.
Hematological tests should be performed on at least ten F1 animals per sex per group during the first 2 weeks
of study, and at 3, 6 and 12 months during the study. If data trends or significant parameter changes
(biological or statistical) are observed that are of concern at the 12-month measurement and the study lasts
longer than one-year, an 18-month measurement should be included.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be analyzed
C. Body Weight and Feed Intake Data:
D. Clinical Testing:
1. Ophthalmological Examination:
2. Hematology:
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individually, and not pooled. If, due to the large number of animals, it becomes necessary to draw blood
samples on more than one consecutive day at each sampling point, the samples should be obtained at
approximately the same time each day.
The following determinations are recommended: hematocrit, hemoglobin concentration, erythrocyte count,
total and differential leukocyte counts, mean corpuscular hemoglobin, mean corpuscular volume, mean
corpuscular hemoglobin concentration, platelet count, and a measure of clotting potential (e.g., clotting time,
prothrombin time, activated partial thromboplastin time).
Test compounds may have an effect on the hematopoietic system and therefore appropriate measures should
be employed so that evaluations of reticulocyte counts and bone marrow cytology may be performed if
warranted. Reticulocyte counts should be obtained for each animal using automated reticulocyte counting
capabilities, or from air-dried blood smears. Bone marrow slides for cytological evaluation should be prepared
from each animal. These slides only need to be microscopically examined when effects on the hematopoietic
system are noted.
Clinical chemistry tests should be performed on at least ten F1 animals per sex per group during the first 2
weeks of study, and at 3, 6 and 12 months during the study. If data trends or significant parameter changes
(biological or statistical) are observed that are of concern at the 12-month measurement and the study lasts
longer than one-year, an 18-month measurement should be included.
Ideally, the same rodents should be sampled at each collection time point. Blood samples should be drawn at
the end of the fasting time and before feeding. Fasting duration should be appropriate for the species and the
analytical tests to be performed. Blood samples should be analyzed individually, and not pooled. If animals are
sampled on more than one day during a study, blood should be drawn at approximately the same time each
sampling day.
Clinical chemistry tests that are appropriate for all test substances include measurements of electrolyte
balance, nutrients metabolism, and liver and kidney function. Specific determinations should include:
Hepatocellular evaluation (at least 3 of the following 5)
z Alanine aminotransferase (SGPT, ALT)
z Aspartate aminotransferase (SGOT, AST)
z Sorbitol dehydrogenase
z Glutamate dehydrogenase
z Total bile acids
Hepatobiliary evaluation (at least 3 of the following 5)
z Alkaline phosphatase
z Bilirubin (total)
z Gamma-glutamyl transpeptidase (GG transferase)
z 5' nucleotidase
z Total bile acids
Other markers of cell changes or cellular function
z Albumin
z Calcium
z Chloride
z Cholesterol (total)
z Cholinesterase
z Creatinine
z Globulin (calculated)
z Glucose
z Phosphorous
z Potassium
z Protein (total)
3. Clinical Chemistry:
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z Sodium
z Triglycerides
z Urea nitrogen
z The FDA understands that the specific nature of the test substance may warrant the
consideration of alternative tests. Appropriate justification for alternative tests should be
presented in study reports.
In spite of standard operating procedures and equipment calibration, it is not unusual to observe considerable
variation in the results of clinical chemistry analyses from day to day. [2] Ideally, clinical chemistry analyses
for all dose groups should be completed during one day. If this is not possible, analyses should be conducted
in such a way as to minimize potential variability.
The determination of volume of urine collected, urine specific gravity, pH, glucose, and protein, as well as
microscopic analysis of urine for sediment and presence of blood and/or blood cells, are recommended[14]
during the first 2 weeks of study, and at 3, 6 and 12 months during the study. If data trends or significant
parameter changes (biological or statistical) are observed that are of concern at the 12-month measurement
and the study lasts longer than one-year, an 18-month measurement should be included. These tests should
be performed on at least ten F1 animals per sex per group.
These animals should be killed after selection of the F1 animals to be continued on studying. If toxic signs or
reproductive toxicity are observed, these animals should be subject to a complete gross necropsy.
All of these F1 animals should be subjected to complete gross necropsy, including examination of external
surfaces, orifices, cranial, thoracic and abdominal cavities, carcass, and all organs. The gross necropsy should
be performed by, or under the direct supervision of, a qualified pathologist, preferably the pathologist who will
later perform the microscopic examination.
Organs that should be weighed at minimum include the adrenals, brain, epididymides, heart, kidneys, liver,
spleen, testes, prostate, thyroid/parathyroid, thymus if present, ovaries and uterus. Before being weighed,
organs should be carefully dissected and trimmed to remove fat and other contiguous tissue. Organs should
be weighed immediately after dissection to minimize the effects of drying on organ weight.
Generally, the following tissues should be fixed in 10 % buffered formalin (or another generally recognized
fixative) and sections prepared and stained with hematoxylin and eosin (or another appropriate stain) in
preparation for microscopic examination. Lungs should be inflated with fixative prior to immersion in fixative.
z Adrenals
z Aorta
z Bone (femur)
z Bone marrow (sternum)
z Brain (at least 3 different levels)
z Cecum
z Colon
z Corpus and cervix uteri
z Duodenum
z Epididymides
z Esophagus
4. Urinalyses:
VI. Necropsy and Microscopic Examination
A. Gross Necropsy
Termination of Parental and F1 Animals not Selected for the Post-Weaning Phase
Termination of F1 Animals Selected for the Post-Weaning Phase
B. Organ Weight
C. Preparation of Tissues for Microscopic Examination
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z Eyes
z Gall bladder (if present)
z Harderian gland
z Heart
z Ileum
z Jejunum
z Kidneys
z Liver
z Lung (with main-stem bronchi)
z Lymph nodes (1 related to route of administration and 1 from a distant location)
z Mammary glands
z Nasal turbinates
z Ovaries and fallopian tubes
z Pancreas
z Pituitary
z Prostate
z Rectum
z Salivary gland
z Sciatic nerve
z Seminal vesicle (if present)
z Skeletal muscle
z Skin
z Spinal cord (3 locations: cervical, mid-thoracic, and lumbar)
z Spleen
z Stomach
z Testes
z Thymus (if present)
z Thyroid/parathyroid
z Trachea
z Urinary bladder
z Vagina
z Zymbal's gland
z All tissues showing abnormality
All gross lesions should be examined microscopically. All tissues from the F1 animals in the control and high
dose groups should be examined. If treatment related effects are noted in certain tissues, then those specific
tissues in the next lower dose level tested should be examined. Successive examination of the next lower dose
level continues until no effects are noted. In addition, all tissues from both parental and F1 animals that died
prematurely or were sacrificed during the study should be examined microscopically. If there are questions
related to the review and interpretation of pathological lesions and statistical results, additional discussion
may be found in Chapters IV.B.3. 12 and IV.B.4. 13 of the Redbook 2000.
Histopathology evaluation of the lymphoid organs should be performed as described in the section on
immunotoxicity testing (see Chapter V.D. of the 1993 draft Redbook II). A recent publication provides further
discussion on this subject. [17]
1 Clinton S.K., A.L. Mulloy, S.P. Li, H.J. Mangian and W.J. Visek, Dietary Fat and Protein Intake Differ in
D. Microscopic Evaluation
E. Histopathology of Lymphoid Organs
VII. References
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Modulation of Prostate Tumor Growth, Prolactin Secretion and Metabolism, and Prostate Gland Prolactin
Binding Capacity in Rats, The Journal of Nutrition, 127:225-237, 1997.
2 Gaylor D.W., R.L. Suber, G.L. Wolff and J.A Crowell, Statistical Variation of Selected Clinical Pathological and
Biochemical Measurements in Rodents, Proceedings of the Society for Experimental Biology and Medicine,
185:361-367, 1987.
3 International Conference on Harmonization (ICH), Technical Requirements for Registration of
Pharmaceuticals for Human Use, ICH Harmonized Tripartite Guideline, S1B: Testing for Carcinogenicity of
Pharmaceuticals, 1997.
4 ICH, Technical Requirements for Registration of Pharmaceuticals for Human Use, ICH Harmonized Tripartite
Guideline, S1C(R): Addendum: Addition of a Limit Dose and Related Notes, 1997.
5 ICH, Technical Requirements for Registration of Pharmaceuticals for Human Use, ICH Harmonized Tripartite
Guideline, S1C: Dose Selection for Carcinogenicity Studies of Pharmaceuticals, 1994.
6 International Life Sciences Institute (ILSI)/Health and Environmental Sciences Institute (HESI)), Committee
on Carcinogenicity of Chemicals in Food, Consumer Products and Environment, Statement on ILSI/ HESI
Research Programme on Alternative Cancer Models (Letter to the Editor), Toxicologic Pathology, 31(2):254-
257, 2003.
7 Keenan K.P., C.M. Hoe, L Mixson, C.L. McCoy, J.B. Coleman, B.A. Mattson, G.A. Ballam, L.A. Gumprecht,
and K.A. Soper, Diabesity: A Polygenic Model of Dietary-Induced Obesity from ad libitum Overfeeding of
Sprague-Dawley Rats and its Modulation by Moderate and Marked Dietary Restriction, Toxicologic Pathology,
33:650-674, 2005.
8 Keenan K.P., J.B. Coleman, C.L. McCoy, C.M. Hoe, K.A. Soper and P. Laroque, Chronic Nephropathy in ad
libitum Overfed Sprague-Dawley Rats and its Early Attenuation by Increasing Degrees of Dietary (Caloric)
Restriction to Control Growth, Toxicologic Pathology, 26(6):788-798, 2000.
9 McConnell, E.E., The Maximum Tolerated Dose: the Debate. Journal of the American College of Toxicology, 8
(6):1115-1120, 1989.
10 Organization for Economic Cooperation and Development (OECD), Environment, Health and Safety
Publications, Series on Testing and Assessment No. 35 and Series on Pesticides No. 14, Guidance Notes for
Analysis and Evaluation of Chronic Toxicity and Carcinogenicity Studies, Paris, 2002.
11 OECD, Guideline for Testing of Chemicals, No. 451, Carcinogenicity Studies, Adopted in 1981.
12 OECD, Guideline for Testing of Chemicals, No. 452, Chronic Toxicity Studies, Adopted in 1981.
13 Office of Science and Technology Policy/Executive Office of the President, Chemical Carcinogens; A Review
of the Science and its Associated Principles. The Federal Register 15(50):10372-10442, March 14, 1985.
14 Ragan H.A. and R.E. Weller, Markers of Renal Function and Injury, In: The Clinical Chemistry of Laboratory
Animals, Second Edition, Taylor & Francis, Philadelphia, PA, pp. 520-533, 1999.
15 Rao G.N. and P.W. Crockett, Effect of Diet and Housing on Growth, Body Weight, Survival and Tumor
Incidences of B6C3F1 Mice in Chronic Studies, Toxicologic Pathology, 31(2):243-250, 2003.
16 Scientific Advisory Committee on Alternative Toxicological Methods (SACATM) of the Interagency
Coordinating Committee on the Validation of Alternative Methods, Summary Minutes for March 10 - 11
Meeting, Bethesda, Maryland, 2004.
17 Society of Toxicologic Pathology (STP) Immunotoxicology Working Group (P. HALEY et al.), STP Position
Paper: Best Practice Guideline for the Routine Pathology Evaluation of the Immune System, Toxicologic
Pathology, 33:404-407, 2005.
18 U.S. Department of Health and Human Services (DHHS), Food and Drug Administration (FDA), Center for
Drug Evaluation Research (CDER), Draft Guidance for Industry on Computerized Systems Used in Clinical
Trials; Availability, The Federal Register, 69(191):59239-59240, October 4, 2004.
19 U.S. DHHS, National Toxicology Program (NTP), Descriptions of NTP Study Types, 2-Year Study Protocol,
2004.
20 U.S. DHHS, FDA, CDER, Guidance for Industry, S1B Testing for Carcinogenicity of Pharmaceuticals, 1997.
21 U.S. DHHS, NTP, Board of Scientific Counselors, Report of the NTP Ad Hoc Panel on Chemical
Carcinogenesis Testing and Evaluation, 1984.
22 U.S. Environmental Protection FDA (EPA), Office of Prevention, Pesticides and Toxic Substances (OPPTS),
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4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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7. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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11. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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12. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
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13. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078320.htm
Health Effects Test Guidelines, OPPTS 870.4200: Carcinogenicity, 1998.
23 U.S. EPA, OPPTS, Health Effects Test Guidelines, OPPTS 870.4100: Chronic Toxicity, 1998.
24 U.S. National Academy of Sciences (NAS), National Research Council (NRC), Institute of Laboratory Animal
Resources, Guide for the Care and Use of Laboratory Animals, National Academy Press, Washington, D.C.,
1996.
25 U.S. NAS, NRC, Subcommittee on Laboratory Animal Nutrition, Committee on Animal Nutrition, Board on
Agriculture, Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, National Academy Press,
Washington, D.C., 1995.
26 U.S. NAS, NRC, Issues in Risk Assessment, National Academy Press, pp.15-19 & 43-96, 1993.
Links on this page:
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July 2000
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
In the U. S., the Food and Drug Administration (FDA) is the agency responsible for ensuring that the are safe
for all consumers. In order to determine the safety of these food ingredients for consumption, appropriate
information and results from a series of tests must be made available to the agency. In 1982, in an effort to
provide guidance to the food industry concerning the appropriate tests for the determination of safety, the
FDA issued the Toxicological Principles for the Safety Assessment of Direct Food Additives and Color Additives
Used in Foods, commonly referred to as the Redbook.(23) In 1993, based on the expansion of technology and
the use of food ingredients, as well as the refinement of the scientific criteria for establishing safety, the FDA
updated its guidelines and issued the draft Redbook II.(24) Since the draft Redbook II was issued, additional
refinements have been made in the procedures for the multigeneration reproduction study and for the
assessment of effects on male reproduction. The latest proposed guidelines for multigeneration studies are
provided here, in Redbook 2000.
During the past several decades, the technology of food processing has changed dramatically and the use and
variety of food ingredients have increased. In the U. S., the Food and Drug Administration (FDA) is the agency
responsible for ensuring that food ingredients are safe for all consumers. Safety, as it pertains to food
ingredients , is defined in the Code of Federal Regulations as a "reasonable certainty ... that the substance is
not harmful under the intended conditions of use".(25) In order to obtain a "reasonable certainty" of meeting
the regulation, appropriate information and results from a series of tests must be made available to the
agency. Just as the technology and use of food ingredients have expanded, so the scientific criteria for
establishing safety have also been refined.
In an effort to provide guidance to industry concerning the appropriate tests for the determination of safety,
the FDA issued the Toxicological Principles for the Safety Assessment of Direct Food Additives and Color
Additives Used in Foods.(23) The book is commonly referred to as the Redbook. In 1993, based on increased
knowledge of toxicological processes and procedures as well as changes in the food industry, the FDA updated
its guidelines and issued the draft Redbook II. (24)
In 1982, a three-generation reproduction study in rats was recommended, with a teratology phase as part of
the battery of tests for substances in concern levels two and three. In 1993, a multigeneration reproduction
study with a teratology phase for concern levels two and three was still required, but the multigeneration
Redbook 2000: IV.C.9.a Guidelines for Reproduction Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.9.a. Guidelines for Reproduction Studies
I. Abstract
II. Introduction
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
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study was streamlined to two generations with a single litter per generation.
Concern levels, as determined by the agency, are "relative measures of the degree to which the use of an
additive may present a hazard to human health".(24) The concern level is based on the extent of human
exposure (dose) and the toxicological effects on biological systems. There are three broad bands of concern
levels. Concern level three represents the highest probable risk to human health. Concern level one represents
the lowest probable risk. Concern level two is intermediate between high and low risk.
Draft Redbook II also included general guidelines for assessing effects on male reproductive function and
optional neurotoxicity and immunotoxicity screens. Since Draft Redbook II was released, additional
refinements have been made in the procedures for the multigeneration reproduction study and for the
assessment of effects on male reproduction. The latest proposed guidelines for multigeneration studies are
provided here.
In a multigeneration reproduction study, the test substance is administered to parental (F 0
) males and
females prior to and during mating, gestation, and through the weaning of F1 offspring. The test substance is
then given to selected F1 generation offspring during their growth and development to adulthood, and through
the mating period. Pregnant F 1 generation females continue to receive the test substance throughout
gestation and until the F 2 generation offspring until the offspring are weaned.
The guideline for reproduction studies detailed below pertains to substances given orally to rodents. It is
designed to evaluate the effects of a test substance on the reproductive systems of both males and females,
the postnatal maturation and reproductive capacity of offspring, and possible cumulative effects through
several generations. A study can provide information concerning the effects of a substance on gonadal
function, estrous cycles, mating behavior, conception, parturition, neonatal morbidity, mortality, lactation,
weaning, growth and development of the offspring, and target organs in the offspring. The study may also
serve as a guide for subsequent tests. The end points evaluated and the indices calculated must provide
sufficient information and statistical power to permit the FDA to determine whether the chemical is associated
with changes in reproduction and fertility. Additional and historical information is found in Collins,(4) Francis
and Kimmel, (6) and U.S. Environmental Protection Agency.(21)
The minimal reproduction study recommended consists of two generations, with one litter per generation (see
Figure 1). If results of developmental and other toxicity tests indicate that a test substance may be associated
with developmental toxicity, the minimal reproduction study should be expanded. This guideline contains
optional procedures for inclusion of additional litters per generation, additional generations, a test for
teratogenic and developmental toxicity effects, optional neurotoxicity screening, and optional immunotoxicity
screening.
Figure 1. 2-Generation Reproduction and Teratology Study
The following recommendations are applicable to all FDA toxicity studies:
1. 	Studies should be conducted according to Good Laboratory Practice Regulations (GLPs). (22)
2. 	Animals should be cared for, maintained, and housed according to the recommendations contained in the
Guide for the Care and Use of Laboratory Animals.(10)
3. 	Healthy animals that have not been subjected to previous experimental procedures should be used.
Generally, it is not possible to treat animals for infection during the course of a study without the risk of
interaction between the treatment drug and the test substance. The females should not be pregnant and
should be nulliparous.
4. 	Test animals should be characterized by reference to their species, strain, sex, and weight or age.
5. 	Animals should be assigned to control and experimental groups in a stratified random manner to
minimize bias and ensure compatibility across experimental and control groups for statistical purposes.
Each animal must be assigned a unique number.
A dose range-finding study is recommended to determine the most appropriate doses, unless suitable
III. Guideline for Reproduction Studies
A. General Recommendations
B. Dose Range-Finding Study
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pharmacokinetic and metabolic data concerning the test substance are available prior to the start of the study.
The dose range-finding study should preferably, but not necessarily, be done in pregnant animals. Comparison
of the results from a trial study in non-pregnant animals and a main study in pregnant animals should
establish whether the test substance is more or less toxic in pregnant animals than in non-pregnant animals.
Because of the expense and length of time needed for multigeneration studies, the species selected should be
one that will yield the greatest amount of information per unit cost. Rodents such as rats and mice are usually
selected for use in multigeneration studies. The rat is the preferred species because of the small size of the
animals, ease of breeding in the laboratory, gestation length of approximately three weeks, high fertility rate,
and spontaneous ovulation. The litters are large enough to allow for inter- and intra-litter comparisons, and
the animals are less susceptible to stress effects than are mice. Strains with low fecundity should not be used.
Single housing of the animals is recommended, except during mating. The animals' diet should meet all
nutritional requirements to support pregnancy and lactation in the test species.
Exposure to the test substance typically begins when the rats are five to nine weeks of age. All test and
control animals should be acclimated to the study conditions before treatment begins. The acclimation period
is usually one week except under unusual conditions. Each test and control group should consist of animals of
uniform weight and age and should start with a number of animals sufficient to contain approximately 20
males and 20 pregnant females near term. In order to achieve this number, it is usually necessary to start
with 30 animals per sex per group in the first parental group (F 0
) and 25 animals per sex per group (at least
one male and one female from each litter, with a maximum of two of each sex per litter) in the parents of
each consecutive generation.
Animals should be assigned to test and control groups in a stratified random manner to minimize intergroup
weight differences. Each animal should be uniquely identified and the litter of origin for each F1 animal should
be identified.
A minimum of three doses of the test substance (high, intermediate, and low doses) should be used to
facilitate the separation of dose-related responses from experimental variation. The high dose should produce
some parental toxicity (such as reduced body weight or weight gain) but not more than 10% parental
mortality. The dose should not exceed 5% of the diet for non-nutritive additives. In dietary studies for
macronutrient additives, high doses should be based on nutritional effects rather than toxicological end points.
The lowest dose should not induce observable adverse parental effects and should be set at a level which is
expected to provide a minimal margin of safety. The intermediate dose(s) should be spaced to allow an
arithmetic or geometric progression between the high and low doses. The addition of one or more extra
groups is preferable to large intervals between doses.
A concurrent control group is required. Control animals should be fed and handled the same as dosed animals
and should be caged in such a way as to preclude airborne or other contamination by the test substance. For
dietary studies, the control group should be fed the basal diet. When a carrier vehicle for the test substance is
used, the volume of vehicle given to control rats should be equal to the maximal amount of vehicle given to
any dosed group. If there are insufficient data on the toxic properties of the vehicle used in administering the
test substance, a sham control group could be included. An additional control group that is not exposed to the
vehicle should be included in the study. If a test substance causes reduced dietary intake, a pair-fed control
group should be considered.
Animals should be exposed to the test substance during the entire study. Males of the first parental group (F 0
)
should be dosed for the duration of spermatogenesis and epididymal transit (at least ten weeks) before
mating and throughout the mating period, in order to detect adverse effects on spermatogenesis by the test
C. Main Study
1. Experimental Animals, Species and Strain Selection and Housing
2. Number, Sex, and Age
3. Assignment to Dose Groups
4. Dose Selection
5. Control Group(s)
6. Duration of Testing
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substance. The first parental females (F0
) should be exposed before mating for the same length of time (at
least ten weeks) as the males and then through mating and pregnancy, to the weaning of the F1a litter. Litters
(usually F1a and F 2a
) should be exposed from the prenatal period throughout their entire postnatal lives. If a
third generation is planned, these litters also should be exposed from the prenatal period and throughout their
entire lives.
The test substance may be administered to rodents in the diet, in drinking water, or by gavage (stomach tube
intubation). The same route of administration should be used for all animals throughout the study. If the test
substance is given by gavage it is best to adjust the volume daily or every three days based on the animal's
body weight.
For each mating, a female should be placed with a single randomly selected male (one:one mating) from the
same dose group until pregnancy occurs or two to three weeks have elapsed. Mating of one male with two
female rats is permitted in the event that a male dies.
Animals should be separated as soon as possible after evidence of copulation has been observed. If mating
has not occurred after two to three weeks, the animals should be separated without further opportunity for
mating. Mating pairs should be clearly identified in the data. Each morning, all females should be examined for
the presence of sperm in the vaginal lavage or the presence of a vaginal plug; if sperm and/or a vaginal plug
are found, this is considered day zero of gestation. Near parturition, pregnant females should be caged
separately in delivery or maternity cages and may be provided with nesting materials. Pregnant females in
test and control groups should be allowed to litter normally.
Standardization of the number of pups per litter through culling is optional. Litters may be standardized to ten
(or eight) based on historical litter size for the strain. It is recommended that standardization be performed on
postnatal day four by reducing all litters of more than ten (or eight) to ten (or eight) in a random manner. If
possible, the retained litter-mates should consist of equal numbers of males and females. Random selection is
important to guard against the human tendency to keep the most fit animals in the study.
At least one male and one female should be randomly selected from each litter for mating with another pup of
the same dose level but different litter to produce the next generation. If there are insufficient litters from
which to make a selection, then no more than two males and two females per litter should be included in the
group. As many litters as possible should be represented. The mating procedures for the F1 males and females
should be carried out in the same manner as the F0 parental animals. Care should be taken that siblings are
not mated on a study. F 1 males and females not selected for mating should be terminated after weaning.
If overt reproductive, morphologic, and/or toxic effects of a test substance are observed in offspring during
the two-generation reproduction study, the study may be extended to a third generation to determine
cumulative effects of the substance. Selection of animals for mating and mating for an additional generation
should be carried out by the same procedures as for the first generation. Randomly mated animals from the
F2a litter should be mated to produce the third generation. F 3a animals should be weaned and either
necropsied or used for a longer-term toxicity study.
If production of a second litter is necessary, the dams should be mated again approximately one to two weeks
after weaning of the F1a or F 2a litter.
The teratology phase should be incorporated into the multigeneration reproduction study unless justification
can be provided for conducting a separate developmental study. In a reproduction study, either the F2b or the
F3b litter can be used to determine fetotoxic effects of the test substance. If a teratology phase is to be
performed, pregnancy should be timed by the presence of sperm in the vaginal lavage or by the presence of a
vaginal plug, and this considered as day zero of gestation. Approximately one day before expected parturition,
the dams should be euthanized and Cesarean sections performed. The uterus should be opened and examined
7. Substance Administration
8. Mating Procedures
9. Standardizing the Number of Pups per Litter
10. Selection of Parental Animals for Next Generation
11. Optional Third Generation
12. Optional Second Mating
13. Optional Teratology Phase
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for the presence of early and late deaths, and corpora lutea should be counted. Each live fetus should be
removed from the uterus. The weight and sex of each live fetus should be determined. Each live fetus should
be examined for gross malformations and then for skeletal or soft-tissue abnormalities. Additional, detailed
procedures are found in the Food and Drug Administration Proposed Testing Guidelines for Developmental
Toxicity Studies.(13)
Each animal should be observed at least twice each day. The first observation should be a thorough clinical
examination. The second may involve the observation of the animals through their cages. Observation of the
animals through their cages is satisfactory for pregnant animals near term and for animals nursing their
litters. Observation times should be selected to permit detection of the onset and progression of all toxic and
pharmacologic effects of the test substance and to minimize the loss of animals and organs/tissues. Relevant
behavioral changes and all signs of toxicity, including mortality, should be recorded. Estrous cycle length and
normality should be evaluated daily by vaginal smears for all F0 and F 1 females during a minimum of three
weeks prior to mating and during cohabitation. The duration of gestation should be calculated from day zero
of pregnancy. Care should be taken to prevent the induction of pseudopregnancy.
Individual records should be maintained for all adult animals and offspring selected for the next generation.
Toxicological and pharmacological symptoms and signs, including behavioral abnormalities, should be
recorded daily; records should include the date of onset, duration, and intensity of symptoms and signs.
Animals should be weighed immediately before the test substance is first administered, once weekly
thereafter, and at necropsy. Feed consumption also should be recorded weekly at a minimum. If the
substance is given in the diet, weekly body weights are acceptable. If the substance is given by gavage it is
best to adjust the volume daily or every three days on the basis of the animal's body weight. Water
consumption should be measured if the test substance is administered in the water and may also be measured
if it is thought that the substance might influence fluid consumption.
Each litter should be examined as soon as possible after delivery for the number of pups, stillbirths, live
births, and the presence of gross anomalies. Dead pups should be necropsied and observed for possible gross
defects and the cause of death unless excessive autolysis renders specimens useless.
The neonates should be carefully observed, and their sex and weight should be noted on postnatal days zero
(day of birth), four, seven, fourteen, and 21. Other appropriate days are acceptable to monitor postnatal
growth and other developmental indices.
Anogenital distance should be measured at day zero for all F2 pups that show treatment-related effects in F1
sex ratio or sexual maturation. The age and weight of each animal on the day of vaginal opening or balano-
preputial separation should be recorded for F1 weanlings selected for mating.
Multigeneration reproduction studies provide an excellent vehicle to screen for potential developmental
neurotoxicity. Periodic examination of the developing offspring provides information to help detect treatment-
related changes in development, the appearance of neurological disorders, and other signs of nervous system
toxicity. The examination of the offspring should be as brief as possible to minimize the period of separation
from the dam. During the examination, any abnormalities in the animal's appearance or behavior should be
noted as well as markers to gauge age-appropriate physical development (such as eye opening, genital
development, and incisor eruption) and functional development (such as righting reflex, startle response, and
motility). As an alternative option, satellite groups of litters (using suitable numbers for adequate statistical
analysis) may be used to screen for developmental neurotoxicity. The inclusion of other endpoints should be
encouraged, such as the assessment of cognitive function development. All data derived from the examination
of the experimental offspring, including positive and negative findings, should be documented, statistically
analyzed as appropriate, using the litter as the statistical unit, and reported. Additional information is available
in Sobotka et al.(19)
Multigeneration reproduction studies can screen the effects of a test substance on a developing immune
system and evaluate the potential for immunotoxicity by the use of non-invasive (Type I) tests and invasive
(Type II) tests. (24) Since the effects of in-utero exposure are not normally assessed in chronic, acute, and
subchronic studies, Type I immunotoxicity testing should be conducted on exposed dams and F1 male and
14. Clinical Observations
15. Growth of Offspring
16. Optional Neurotoxicity Screening
17. Optional Immunotoxicity Screening
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female offspring. By careful planning, animals used or produced in the reproduction study may be evaluated
for Type I indicators, and possibly Type II. For example, when F0 parental males have completed the mating
cycle, representative animals could be sacrificed or fed longer if data from chronic, acute, and subchronic
studies are not available. After weaning, F 0 parental females that are no longer needed are an excellent
source of animals for evaluating potential immunotoxicity effects. For evaluating the effects of in-utero
exposure, neonatal specimens from culled litters could be used for histologic evaluation of the neonatal
lymphoid organs. Only a small number of weanlings of each sex are selected for further use in the
reproduction study; the remaining animals could be sacrificed and evaluated at three weeks or allowed to
mature to six or eight weeks of age. At this time, Type I testing and/or functional Type II testing could be
performed. Similar opportunities exist in the F2 generation. Additional information is available in Hinton et al.
(9)
All adult males and females should be terminated when they are no longer needed for the assessment of
reproductive findings. Any dam that shows signs of imminent abortion, premature delivery, or moribund
condition should be necropsied on the day such signs are observed. Dead pups (pups that die spontaneously
during the postpartum phase) should be necropsied and observed for possible gross defects and the cause of
death unless they are excessively autolyzed.
At the time of termination, all parental animals should be examined macroscopically for any structural
abnormalities or structural changes. This should include examination of external surfaces, orifices, cranial
cavity, carcass, and all organs. Special attention should be paid to the organs of the reproduction system. The
uterus should be examined for the presence of implantation sites and resorptions. The uterus may be stained
with sodium or ammonium sulfide (16) or other appropriate chemical to help visualize the implantation sites.
a. 	Necropsy of Weanlings
At the time of termination, at least two pups per sex per litter from unselected F1 and F 2 weanlings
should be examined macroscopically for any structural abnormalities or structural changes. Special
attention should be paid to the organs of the reproduction system.
Brain, thymus, and spleen should be weighed from the F1 and F 2 weanlings that are examined
macroscopically for structural abnormalities or structural changes. At necropsy, grossly abnormal organs
and tissues from pups from all dose groups should be preserved and then examined histopathologically.
b. 	Necropsy of Parental Animals
At necropsy, the following organs of all F 0 and F 1 control and treated parental animals should be
observed and weighed: brain, pituitary, liver, kidneys, adrenal glands, spleen, known target organs, and
reproductive organs. Uterus and ovaries of females should be weighed. For males, both testes, seminal
vesicles with coagulating glands, and the prostate should be weighed. In addition, the total epididymal
weight should be determined for one epididymis that will be fixed for histopathology, and both total
epididymal and cauda epididymal weight should be determined for the epididymides that will be used for
observing sperm morphology, numbers, and motility. Seminal vesicles and prostates should be weighed
separately. The source of the prostate weight should be identified (e.g., as ventral and/or dorsal and/or
dorsolateral prostate). At necropsy, the contralateral testis and epididymis (the non-fixed testis and
epididymis) should be utilized for the determination of homogenization resistant spermatid numbers and
cauda epididymal sperm reserves, respectively. Additionally, sperm from the cauda epididymis (or
proximal vas deferens) should be collected for the evaluation of sperm motility and sperm morphology.
Since testis weight varies only slightly within a given species, a change in testis weight may indicate that
a test substance has had an adverse effect on the testis. Seminal vesicles and prostates are androgen-
dependent organs and changes in their weights may indicate a change in the endocrine status of the
animal or the ability of the testis to produce androgen.
Organ weight should be reported as absolute weight and as a relative weight (e.g., organ-to-body or
organ-to-brain weight).
i. 	Fixation of Tissues and Organs
At necropsy, the following organs and tissues, or representative samples thereof, from all parental
animals, should be fixed and stored in a medium suitable for histopathological examination. For
parental females, the vagina, uterus with cervix, ovaries with oviducts, adrenal and pituitary
glands, target organs, and grossly abnormal tissue should be preserved. For parental males, one
testis, one epididymis, seminal vesicles, coagulating glands, prostate, and adrenal and pituitary
18. Gross Necropsy and Microscopic Examination
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glands, target organs, and grossly abnormal tissue should be preserved. Testicular tissues should
be fixed in Bouin's or a comparable fixative and stored in a suitable medium for histopathological
examination. Several articles and books have been written recently to describe methods that can
be used to preserve testicular tissue and evaluate histopathology. (8),(15) If an immunotoxicity
screen is being included in the study, the appropriate procedures and organs mentioned in
Redbook II(24) should be followed.
ii. 	General Histopathology
Full histopathological examination of the organs should be performed for ten randomly selected
control and high-dose F 0 and F 1 animals per sex. If the high-dose group reveals a treatment-
related effect, ten animals from each intermediate dose group should be randomly selected and
examined. Tissues and organs preserved from the additional animals in each group may be
examined to provide additional data.
In addition, a full histopathological examination should be performed on the reproductive organs of
animals suspected of reduced fertility from intermediate dose groups. Signs of reduced fertility
include failure to mate, conceive, sire, or deliver healthy offspring; effects on estrous cycle;
reduced reproductive organ weight; and reduced testicular spermatid counts or cauda epididymal
sperm counts.
iii. 	Histopathology of Female Reproductive Organs
The post-lactational ovary should contain primordial and growing follicles as well as the large
corpora lutea of lactation. Histopathological examination should detect qualitative depletion of the
primordial follicle population. A quantitative evaluation of primordial follicles should also be
conducted. If the high-dose animals reveal a treatment-related effect, all groups should be
examined. The following evaluation technique may be used, but others may be used if the number
of animals, ovarian section selection, and section sample size are statistically appropriate.
Substance-induced depletion of primordial follicles can be identified by removing five sections from
the inner third of each ovary. The sections should be at least 0.1 mm (100 μm) thick. Examination
should include enumeration of the total number of primordial follicles from these ten sections for
comparison with control ovaries. Examination should also confirm the presence or absence of
growing follicles and corpora lutea in comparison with control ovaries. Additional information can
be found in Bolon et al.,(1) Bucci et al.(2) and Heindel. (7)
iv. 	Histopathology of Male Reproductive Organs
Histopathological assessment of the epididymis should include an evaluation of the corpus, cauda
and caput epididymis. This can be accomplished by examining a longitudinal section through all
three regions of the epididymis in order to identify such lesions as sperm granulomas, leukocyte
infiltration, aberrant cell types within the lumen, or the absence of clear cells in the cauda
epididymal epithelium.(5)
Careful histopathological examination of the testis is recognized as a sensitive method to identify
effects on spermatogenesis. Testicular tissue should be examined with a knowledge of testis
structure, the process of spermatogenesis, and the classification of spermatogenesis. If an effect is
observed, it should be described in detail. (15) If testicular effects are quantitated, the methods
used should be described in detail.
A thorough histological evaluation of the testis should include an examination of the interstitial
compartment and the seminiferous tubule compartment. A histopathological evaluation of the
intertubular cell compartment of the testis should include a general assessment of the Leydig cells,
the blood vessels, and the cell types other than the Leydig cells typically found in the intratubular
space. The general appearance of the seminiferous tubules should be noted This should be followed
by an examination of the seminiferous tubule compartment to detect any disruption in the normal
sequence of the events that occurs during the normal process of spermatogenesis. The
seminiferous epithelium should then be carefully observed to detect any of the following: presence
of multinucleated cells, missing germ cell layers, increased germ-cell degeneration, abnormal
development in germ cells, sperm release delay or failure, presence of germ cells in the
seminiferous tubule lumen, and any changes in the Sertoli cells (vacuolization, sloughing, or
nuclear changes). The general condition of the boundary layer should be noted.
D. End Points of Female Reproductive Toxicity
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End points of reproductive toxicity are usually expressed as indices that encompass the animals' responses to
the test substance from conception to weaning. The following indices should be calculated for each
reproduction study: female fertility, gestation, and live-born indices; weaning index or lactation index; sex
ratio; and viability indices at postnatal days four, seven, fourteen, and 21.
The female fertility index represents the percent of matings that result in pregnancies. It is calculated as
follows: (number of pregnancies/number of matings) X 100. This index reflects the total number of dams that
have achieved pregnancy, including those that deliver at term, abort, or have fully resorbed litters. This index
depends on male libido and fertility as well as female cyclicity and receptiveness.
The gestation index evaluates the efficiency of pregnancy that results in at least one live offspring. In this
index, the litter with one live offspring is counted the same as one with more than one live offspring. The
index is calculated as follows: (number of litters with live pups/number of pregnancies) X 100.
Related to the gestation index, the live-born index (number of pups born alive/total number of pups born) X
100 is a measure of the total number of offspring lost, regardless of litter.
The weaning index represents the ability of pups to survive from day four to day 21. It is calculated as
follows: (number of pups alive at day 21/number of pups alive and kept on day four) X 100. This index
corrects for the reduction of pups on day four. If the pups are not reduced, a related index, the lactation
index, is calculated: (number of pups alive on day 21/number of pups alive on day four) X 100. Regardless of
the etiology, a decrease in the weaning index indicates adverse reproductive effects.
Determining the sex of pups at birth and verifying their sex at each weighing permits the relative fitness of
each sex to be calculated as the offspring mature. The sex ratio is useful in detecting if the test substance is
preferentially affecting one sex. This parameter is usually calculated as follows: (number of males/number of
females). The related calculation (number of females or males/total number of animals) X 100 yields the
percentage of total animals that are male or female.
The viability indices are measures of the offsprings' ability to survive during specific brief intervals of their
lives, from birth (day zero) to day four, day four to day seven, day seven to day fourteen, day fourteen to day
21, or they may reflect longer intervals, such as day zero to day seven, day zero to day 21, etc. For example,
the day seven viability index is calculated as follows: (number of pups alive on day seven/number of pups
alive and kept on day four) X 100. The pups' ability to survive may reflect the adequacy of postnatal
nourishment, maternal neglect, and postnatal absorption of a toxic substance that is excreted in the mother's
milk. Regardless of etiology, decreases in viability indices indicate adverse reproductive effects. Other
appropriate days are acceptable to monitor postnatal growth and other developmental indices.
The following end points of male reproductive toxicity should also be assessed if there is evidence of male-
mediated effects on developing offspring. End points should be measured in all animals in each of the control
and high dose groups. If treatment-related effects are observed, then animals from each intermediate dose
group should be evaluated.
Testicular spermatid enumeration is a measure of sperm production from the stem cells and their survival
through all phases of spermatogenesis. The enumeration of spermatid numbers should primarily be used in
chronic studies where spermatid numbers have stabilized; in short-term studies treatment may not have
impacted the late spermatid population. From the number of spermatids per testis, the efficiency of sperm
production and daily sperm production rate can be calculated.(14)
The second testis (first testis was used for histopathology) from all F0 and F 1 generation males used for
1. Female Fertility Index
2. Gestation Index
3. Live-born Index
4. Weaning Index
5. Sex Ratio and Percentage by Sex
6. Viability Indices
E. End Points of Male Reproductive Toxicity
1. Evaluation of Testicular Spermatid Numbers
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mating should be collected and stored frozen until testicular spermatid numbers are enumerated.
Homogenization-resistant spermatid numbers may be determined by enumerating elongated spermatid nuclei
after the testis has been homogenized in a medium containing detergent.(14)
Motility is influenced by abstinence, the time between obtaining and evaluating the sample, pH of the medium,
sample chamber depth, and temperature. Sperm samples obtained from the cauda epididymis (or proximal
vas deferens) should be collected and evaluated for the percent of progressively motile sperm. (17) Care
should be taken to avoid artifactual cell death during sample preparation so that the percentage of
progressively motile sperm from control animals is consistently high (>70%).(11)
Sperm motility can be assessed by microscopic techniques or with a computer-assisted sperm analysis (CASA)
system. (17) For microscopic evaluation, an acceptable counting chamber of sufficient depth is used to combine
the assessment of motility with sperm numbers and sperm morphology. When the CASA system is utilized, (3),
(18),(20) the derivation of progressive motility relies on user-defined thresholds for average path velocity and
straightness or linear index. All samples should be videotaped or otherwise recorded. The video may be
retained as raw data. In the event that sperm motility is not videotaped, then a sperm motility assessment
from all animals in all dose levels should be performed.
Inasmuch as sperm morphology in rodents is generally stable, characteristic of the animal strain, and exhibits
little variability, an increase in the number of morphologically abnormal sperm indicates that the test
substance has gained access to the germ cells. This should be considered an adverse reproductive effect.
Sperm should be collected from all F0 and F 1 generation males selected for mating from the control and all
dose levels for sperm morphology analysis.
Sperm (minimum 200 per sample) from the cauda epididymis or proximal vas deferens should be examined
as a fixed wet preparation (12),(17) and classified as either normal (both head and midpiece appear normal) or
abnormal (i.e., fusion, isolated heads, misshapen heads and/or tails). (26)
The total number of sperm in the cauda epididymis should be enumerated.(14) Cauda sperm reserves can be
derived from the concentration and volume of sperm in the suspension used to complete the qualitative
evaluations, and the number of sperm recovered by subsequent mixing and/or homogenizing the remaining
cauda tissue. Sperm in the concentrated suspension can be frozen for subsequent evaluation of cauda
epididymal sperm numbers. If sperm counts are reported in relation to the weight of the epididymis, the
absolute counts should be reported in order to clarify declines in sperm number.
Values from control and test groups of animals should be compared statistically. The following techniques may
be used, but others may be substituted if they are appropriate. The fertility and gestation indices may be
analyzed by a one-tailed Fisher exact test. For the sex ratio index, a two-tailed Fisher exact test may be used.
Data for the viability and weaning indices may be transformed by the Freeman-Tukey arc-sine transformation
for binomial proportions. The transformed data may then be analyzed by an analysis of variance (ANOVA)
followed by a one-tailed protected least significant difference (LSD) test to compare the control with the
treated groups if the ANOVA p<0.10. The average litter size and the number of viable pups throughout the
reproduction phase may be analyzed by ANOVA followed by a protected LSD test (one-tailed). For the growth
(weight gain) and organ weight analyses, an analysis of covariance may be used followed by a protected LSD
test (two-tailed) to compare the control and treated groups.
Reports of all reproduction studies should contain the information required by the Good Laboratory Practice
Regulations, including a copy of the study protocol and all amendments, absolute values for all parameters,
complete data (individual pups) and tables of data summarized and analyzed by litter. Because the maternal
animal and not the developing organism is the individual treated during gestation, data generally should be
calculated as incidence per litter or as number and percent of litters with particular end points. All major
indices and end points discussed in the previous section should be calculated. The dosage rate of test
substance (doses) should be reported as mg/kg/day (milligrams of test substance per kilogram of body weight
per day).
Problems commonly encountered in the review of multigeneration reproduction studies include: insufficient
numbers of pregnant animals per control or treatment group, non-random selection procedures, and statistical
analyses of data on a per-pup basis instead of a per-litter basis. Careful consideration of recommended
guidelines and the submission of protocols for review by FDA before conducting the studies should help
2. Sperm Evaluation for Motility, Morphology and Numbers
F. Analysis of Data
G. Reporting the Results of Reproduction Studies
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eliminate such problems.
In addition to the various indices in reproduction studies, data on the average number of pups that survived
during a specific interval (e.g., average number of pups that survived from birth to day four, or the average
number of pups that were weaned) should be examined. This analysis considers the total effect of the test
substance at all stages to that point and is a more sensitive indicator than each index separately.
Relevant historical control data may be used to increase the understanding of the study results. When used,
historical data should be compiled and presented with appropriate additional information, such as dates of
study, strain of animals, vehicle, and route of administration.
1. 	Bolon, B., Bucci, T.J., Warbritton, A.R., Chen, J.J., Mattison, D.R., and Heindel, J.J. (1997). Differential
Follicle Counts as a Screen for Chemically Induced Ovarian Toxicity in Mice: Results from Continuous
Breeding Bioassays. Fundament. Appl. Toxicol. 39:1-10.
2. 	Bucci, T.J., Bolon, B., Warbritton, A.R., Chen, J.J., and Heindel, J.J. (1997). The Effect of Sampling
Procedure on Differential Ovarian Follicle Counts. Repro. Toxicol. 11:689-696.
3. 	Chapin, R.E., Filler, R.S., Gulati, D., Heindel, J.J., Katz, D.F., Mebus, C., Obasaju, F., Perreault, S.D.,
Russell, S., Schrader, S., Slott, V., Sokol, R.Z. and Toth, G. (1992). Methods for Assessing Rat Sperm
Motility. Repro. Toxicol. 6:267-273.
4. 	Collins, T.F.X. (1978). Multigeneration Reproduction Studies. In Handbook of Teratology. Vol 4. (T.G.
Wilson and F.C. Fraser, Eds.), pp. 191-214. Plenum Publishing Co, New York.
5. 	Fawcett, D.W. and Bloom, W. (1986). A Textbook of Histology. W.B. Saunders Publishing, Philadelphia,
PA.
6. 	Francis, E.Z. and Kimmel, G.L. (1988). Proceedings of the Workshop on One- vs Two- Generation
Reproductive Effects Studies. J. Amer. Coll. Toxicol. 7:911-925.
7. 	Heindel, J.J. (1998). Oocyte Quantitation and Ovarian Histology. In An Evaluation and Interpretation of
Reproductive Endpoints for Human Health Risk Assessment. (G. Daston and C. Kimmel, Eds.), pp. 57-74.
International Life Sciences Institute, Health and Environmental Sciences Institute, Developmental and
Reproductive Toxicology Committee, Washington, D. C.
8. 	Hess, R.A. and Moore, B.J. (1993). Histological Methods for Evaluation of the Testis. In Male
Reproductive Toxicology. (R.E. Chapin and J. Heindel, Eds.), pp. 52-85. Academic Press, San Diego, CA.
9. 	Hinton, D.M. (1995). Immunotoxicity Testing Applied to Direct Food and Colour Additives: U.S. FDA
Redbook 2000 Guidelines. Hum. Exper. Toxicol. 14:143-145.
10. 	Institute of Laboratory Animal Resources. (1996). Guidelines for the Care and Use of Laboratory
Animals. National Academy Press, Washington, D. C.
11. 	Klinefelter, G.R., Grey, L.E. and Suarez, J.D. (1991). The Method of Sperm Collection Significantly
Influences Sperm Motion Parameters Following Ethane Dimethanesulfonate Administration in the Rat.
IV. References
Redbook 2000: IV.C.9.a Guidelines for Reproduction Studies
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Repro. Toxicol. 5:39-44.
12. 	Linder, R.E., Strader, L., Slott, V. and Suarez, J.D. (1989). Endpoints of Spermatotoxicity in the Rat
After Short Duration Exposures to Fourteen Reproductive Toxicants. In Reproductive Toxicology. (A.W.
Hayes, Ed.). Raven Press, New York, NY.
13. 	Revision Committee, FDA Guidelines for Developmental Toxicity and Reproduction, Food and Drug
Administration. (1999). Food and Drug Administration proposed testing guidelines for developmental
toxicity studies. Regulat. Toxicol. Pharmacol. 30:39-44.
14. 	Robb, G.W., Amann, R.P. and Killian, G.J. (1978). Daily Sperm Production and Epididymal Sperm
Reserved of Pubertal and Adult Rats. J. Repro. Fertil. 54:103-107.
15. 	Russell, L.D., Ettlin, R.A., Sinha Hakim, A.P., and Clegg, E.D. (1990). Histological and Histopathological
Evaluation of the Testis. Cache River Press, Clearwater, FL.
16. 	Salewski (Koeln), V.E. (1964). Faerbermethode zum Makroskopischen Nachweis von Implantations
Stellen am Uterus der Ratte. Naunyn-Schmeidebergs Archiv Pharmakol. Exper. Pathol. 247:367.
17. 	Seed, J., Chapin, R.E., Clegg, E.D., Darney, S.P., Dostal, L., Foote, R.H., Hurtt, M.E., Klinefilter, G.R.,
Makris, S., Schrader, S., Seyler, D., Sprando, R.L., Treinen, K.A., and Veeranachaneni, R. (1996).
Consensus report: Methods for Assessing Sperm Motility, Morphology, and Counts in the Rat, Rabbit and
Dog. Repro. Toxicol. 10:237-244.
18. 	Slott, V.L., Suarez, J.D. and Perreault, S.D. (1991). Rat Sperm Motility Analysis: Methodologic
Consideration. Repro. Toxicol. 5:449-458.
19. 	Sobotka, T.J., Ekelman, K.B., Slikker, W., Jr., Raffaele, K. and Hattan, D.G. (1996). Food and Drug
Administration Proposed Guidelines for Neurotoxicological Testing of Food Chemicals. NeuroToxicol.
17:825-836.
20. 	Toth, G.P., Stober, J.A., Read, E.J., Zenick, H. and Smith, M.K. (1989). The Automated Analysis of Rat
Sperm Motility Following Subchronic Epichlorohydrin Administration: Methodologic and Statistical
Considerations. J. Androl. 10:401-415.
21. 	U.S. Environmental Protection Agency. (1998). EPA Health Effects Test Guidelines OPPTS 870.3800,
Reproduction and Fertility Effects. 12 pp.
22. 	U.S. Food and Drug Administration. (1978). Good Laboratory Practice Regulations for Nonclinical
Laboratory Studies. U.S. Code of Federal Regulations Title 21 Part 8.
23. 	U.S. Food and Drug Administration. (1982). Toxicological Principles for the Safety Assessment of Direct
Food Additives and Color Additives Used in Food. U.S. Food and Drug Administration, Bureau of Foods,
Washington, DC.
24. 	U.S. Food and Drug Administration. (1993). Toxicological Principles for the Safety Assessment of Direct
Redbook 2000: IV.C.9.a Guidelines for Reproduction Studies
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
Food Additives and Color Additives Used in Food, Redbook II (Draft). U.S. Food and Drug Administration,
Center for Food Safety and Applied Nutrition, Washington, D C.
25. 	U.S. Food and Drug Administration. (1998). General Provisions, Definitions. U.S. Code of Federal
Regulations 21 CFR §170.3, pp. 5-6.
26. 	Zenick, H. and Clegg, E.D. (1986). Issues in Risk Assessment in Male Reproductive Toxicology. J. Amer.
Coll. Toxicol. 5:249-259.
Links on this page:
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July 2000
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
The Food and Drug Administration (FDA) is the agency responsible for ensuring that food ingredients used in
the U.S. are safe for all consumers. In 1982, in an effort to provide guidance concerning appropriate tests, the
FDA issued Toxicological Principles for the Safety Assessment of Direct Food Additives and Color Additives
Used in Food, commonly known as the Redbook.(7) The Redbook included detailed guidelines for testing the
effects of food ingredients on mothers and their developing fetuses. Based on refinements in safety
assessment and risk evaluation as well as expansion of knowledge concerning the metabolism and
pharmacokinetics of food ingredients, the need to revise and update the 1982 document became apparent. In
1993, Redbook II in draft form (8) was made available for public comment. Since then, test end points and
developmental landmarks have been refined. The latest proposed guidelines for developmental toxicity studies
are provided here.
The Food and Drug Administration (FDA) is the agency responsible for ensuring that food ingredients used in
the U.S. are safe for all consumers. In 1982, the FDA issued Toxicological Principles for the Safety Assessment
of Direct Food Additives and Color Additives Used in Food.(7) Based on the color of its cover, the book quickly
became known as the Redbook. The Redbook included detailed guidelines for testing the effects of food
ingredients on mothers and their developing fetuses. The tests included a chapter on
teratology/developmental toxicity studies as well as reproduction studies that spanned several generations.
Guidelines for teratology/developmental toxicity studies are discussed here; guidelines for multigeneration
studies are discussed in Chapter IVC9a 2
.
Based on refinements in safety assessment and risk evaluation as well as expansion of knowledge concerning
the metabolism and pharmacokinetics of food ingredients, the need to revise and update the 1982 document
became apparent. In 1993, Redbook II in draft form was made available for public comment.(8) Changes in
the chapter on reproduction and teratology/developmental toxicity guidelines were based on extensive
literature review and public comments. In late 1996, current drafts of this and several other chapters of
Redbook II were presented at a Redbook Update Symposium and the guidelines were compared with current
draft guidelines from other national and international regulatory groups.(2) Since then, test end points and
developmental landmarks have been refined. The latest proposed guidelines for developmental toxicity studies
are provided here in Redbook 2000.
Redbook 2000: IV.C.9.b Guidelines for Developmental Toxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.9.b. Guidelines for Developmental Toxicity Studies
I. Abstract
II. Introduction
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: IV.C.9.b Guidelines for Developmental Toxicity Studies
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In a developmental toxicity study, the test substance is administered to pregnant animals at least from the
day of implantation to the day prior to the day of expected parturition. A short time before the day of
expected parturition, the pregnant females are euthanized, the uterine contents are examined, and the
fetuses are removed. The fetuses are observed, preserved, and examined for skeletal and soft-tissue
abnormalities.
The purpose of developmental toxicity studies is to evaluate the effects of test substances on developing
fetuses that result from exposure of either parent prior to conception or to mothers during prenatal
development. The adverse effects are as end points that may be used to evaluate the toxic potential of a test
substance. The four major manifestations of an effect on the developing organism are: death, structural
anomaly, altered or retarded growth, and functional deficiency. For many substances, these manifestations
are related to dosage and to the developmental timing and duration of exposure. While high doses produce
death, low doses that permit survival may produce malformed, growth retarded, or functionally deficient
offspring.
The developmental toxicity test may be done as a stand-alone study, or may be part of a multigeneration
reproduction study. If it is combined with a reproduction study, assessment of teratological effects may be
performed on either the first or second generation, but it is usually performed on the last litter of the
generation to maximize exposure to the test agent. As part of a multigeneration study, the fetuses may be
exposed to the test substance from conception. In a stand-alone study, treatment must begin early enough to
include organogenesis for the species used and should continue to the day prior to the expected day of
parturition. This guideline may be used with substances given orally to the rat, mouse, hamster, and rabbit. If
the test substance is believed to have the capacity to alter the rate of its own metabolism through induction of
metabolizing enzymes or as a result of damage incurred by the liver, then consideration should be given to
evaluating the teratogenic potential of the compound by using a separate study.
The following recommendations are applicable to all FDA toxicity studies:
1. 	Studies should be conducted according to Good Laboratory Practice Regulations (GLPs). (6)
2. 	Animals should be cared for, maintained, and housed according to the recommendations contained in the
Guide for the Care and Use of Laboratory Animals.(3)
3. 	Healthy animals that have not been subjected to previous experimental procedures should be used.
Generally, it is not possible to treat animals for infection during the course of a study without the risk of
interaction between the treatment drug and the test substance. The females should not be pregnant and
should be nulliparous.
4. 	Test animals should be characterized by reference to their species, strain, sex, and weight or age.
5. 	Animals should be assigned to control and experimental groups in a stratified random manner to
minimize bias and ensure compatibility across experimental and control groups for statistical purposes.
Each animal must be assigned a unique number.
A dose range-finding study is recommended to determine the most appropriate doses, unless suitable
pharmacokinetic and metabolic data concerning the test substance are available prior to the start of the study.
The dose range-finding study should preferably, but not necessarily, be done in pregnant animals. Comparison
of the results from a trial study in non-pregnant animals and a main study in pregnant animals should
establish whether the test substance is more or less toxic in pregnant animals than in non-pregnant animals.
When pharmacokinetic and metabolic data or other information on the test substance suggest the most
appropriate species for developmental toxicity testing, that species should be used. In the absence of such
data, the preferred species are the rat and rabbit. These guidelines include information on the mouse and
hamster in addition to the rat and rabbit. These animals are small, easy to care for, and have historically
provided consistent results that can be extrapolated to human effects. The strains selected should have high
fecundity and should be sensitive to teratogens and embryotoxins. Scaling of doses between species should be
III. Guideline for Developmental Toxicity Studies
A. General Recommendations
B. Dose Range-Finding Study
C. Main Study
1. Experimental Animals, Species and Strain Selection
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based on pharmacokinetic differences between them, unless precluded by differences in overt toxicity.
Single housing of the animals is recommended, except during mating. Food and water should be provided ad
libitum. The animals' diet should meet all nutritional requirements to support pregnancy in the test species.
Special attention should be paid to diet composition when the test material itself is a nutrient, because such
material may have to be incorporated into the diet at levels which may interfere with normal nutrition. Under
these circumstances, an additional control group fed basal diet may be necessary.
All test and control animals should be young, mature, primiparous, pregnant females of uniform age and size.
A sufficient number of females should be used so that each test and control group consists of approximately
20 pregnant rats, mice, hamsters, or rabbits near term. These are the minimum numbers of pregnant animals
for developmental toxicity testing. The objective is to ensure that enough litters are produced to permit
effective evaluation of the teratogenic potential of the test substance.
The test substance should be administered daily throughout the treatment period. The minimum treatment
period recommended for developmental toxicity studies is from implantation to Cesarean section one day prior
to the expected day of parturition. In rats the approximate timing for this period includes days six through
twenty; in mice, days six through eighteen; in hamsters, days four through fifteen; and in rabbits, days six
through 29. Alternatively, treatment may be extended to include the entire period of gestation, from
fertilization to the day of Cesarean section. If the developmental toxicity test is being conducted as part of a
multigeneration reproduction study, the animals are dosed from before conception until they are necropsied.
The presence of sperm in the vaginal lavage or the presence of a vaginal plug is considered day zero of
gestation.
The test substance or vehicle should be administered by the route that most closely approximates the pattern
of human exposure (diet or drinking water). Oral intubation (gavage) may be appropriate in instances where
human exposure is via a bolus dose or when it is essential for the animal to receive a specified amount of the
test substance. Gavage may also be required when analysis of the agent in the diet is not possible, when the
agent is not stable in the diet, or when the agent is not palatable. The maximum volume of solution that can
be given by gavage in one dose depends on the test animal's size; for rodents, this should not exceed 1
ml/100 g body weight. If the test substance must be given in divided doses, all doses should be administered
within a six-hour period, unless there is justification for increasing the duration of dosing. If the test substance
is given by gavage, it should be given at approximately the same time each day, and the volume should be
adjusted on a daily basis or every three days based on the animal's body weight. In diet and drinking-water
studies, the amount consumed depends on each animal.
In-house mating of the animals is recommended. A sufficient number of males should be mated to ensure a
large gene pool. Siblings should not be mated. Each male may be mated to either one or two females. The
following morning, each female should be examined for the presence of sperm in the vaginal lavage or the
presence of a sperm plug. The presence of sperm in the vaginal lavage or the presence of a vaginal plug is
considered day zero of gestation (day zero of gestation in rabbits is the day insemination is performed or
observed).
Healthy animals should be assigned to test and control groups in a stratified random manner to minimize
inter-group weight differences and ensure statistical comparability of relevant variables. The animals may also
be assigned in a random procedure which results in comparable mean body weight values among all groups.
At least three test groups and one control group should be used in the developmental toxicity study. All
groups should be concurrent.
When the test substance is administered in a vehicle, the vehicle without the test substance should be
administered to the control group at a volume equal to the maximal amount of vehicle given to any dosed
group. If a vehicle or other additive is used to facilitate dosing, the effects on absorption, distribution,
metabolism, or retention of the test substance should be considered, as well as alterations of toxicity due to
2. Animal Husbandry
3. Number, Sex, and Age
4. Duration of Testing
5. Route of Administration
6. Mating Procedures
7. Control and Dosed Groups
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effects on the chemical properties of the test substance. Effects of the vehicle on food consumption, water
consumption, or nutritional status of the animals should also be considered.
If there are insufficient data on the toxic properties of the vehicle used in administering the test substance, a
sham control group should also be included. If no vehicle is used, then the controls should be sham treated.
In all other respects, the control group must be handled and maintained in a manner identical to that used
with the groups given the test substance.
Unless limited by the physical or chemical properties of the substance, the high dose should induce some
developmental and/or maternal toxicity but not more than approximately ten percent mortality. The high dose
should not exceed five percent of the diet for non-nutritive additives. In dietary studies for macronutrient
additives, the high dose should be based on nutritional effects rather than toxicological end points.
The low dose should not induce observable effects attributable to the test substance and should be set at a
level which is expected to provide a margin of safety. The intermediate doses should be spaced to allow an
arithmetic or geometric progression between the low and high doses. The addition of one or more groups is
preferable to the use of large intervals between doses.
End points which may serve as indicators of maternal toxicity include mortality, body weight, body weight
gain, organ weights, feed and water consumption, clinical signs of toxicity, and gross or microscopic lesions.
The calculation of a corrected mean maternal weight gain (difference between initial and terminal maternal
body weight less the gravid uterus weight) may also be used as an index of maternal toxicity.
Various test substances have selective toxic effects on the male, the female, or the offspring, while other
substances exhibit non-specific effects. When mother and offspring are adversely affected by a test substance,
it can be difficult to determine if the developmental toxicity is mediated by maternal toxicity or occurs
independently of it. Due to differences in metabolism, distribution, and elimination of the test substance, the
sensitivity of the maternal system can vary significantly from that of the fetus. The response of the fetus can
also differ markedly from that of the mother as a result of the developmental processes taking place that have
no counterpart in the adult.
Developmental effects without maternal toxicity are commonly regarded as the most serious manifestations of
toxicity, because their occurrence is thought to be the result of greater sensitivity of the developing organism.
When developmental effects are found in the presence of maternal toxicity, the primary cause is often left to
speculation. Without sufficient evidence to support the premise that developmental toxicity is always a
secondary toxic effect in the presence of maternal toxicity, a default is needed. Developmental effects that
occur in the presence of minimal maternal toxicity are thus considered to be evidence of developmental
toxicity, unless it can be established that the developmental effects are unquestionably secondary to the
maternal effects. In situations where developmental effects are observed only at doses where there is a
substantial amount of maternal toxicity, then the possible relationship between maternal toxicity and the
developmental effects should be evaluated in order to make a proper assessment regarding the toxicity of a
test substance.
Throughout the study, each animal should be observed at least twice daily. The first observation should be a
thorough clinical examination. The second may involve observing the animals through the cages. Observation
times should be selected to permit detection of the onset and progression of all toxic and pharmacologic
effects of the test substance and to minimize the loss of animals and organs/tissues. Relevant behavioral
changes and all signs of toxicity, morbidity, or mortality should be recorded.
Dams should be weighed immediately before the first dose of the test substance is administered (usually on
gestation day six for mice, rats, and rabbits; on gestation day four for hamsters), weekly until necropsy, and
at the time of necropsy. If the test substance is given in the diet, weekly body weight is acceptable. If the test
substance is given by gavage, body weights should be measured daily or at least every three days. At a
minimum, weekly measurements of feed consumption should be made. Fluid consumption should be
measured as appropriate. Any dam that shows signs of imminent abortion or premature delivery during the
study should be necropsied on the date such signs are observed.
The test should be terminated approximately one day before the expected day of parturition (day 20 or 21 for
rats, day 29 for rabbits, day eighteen for mice, and day fifteen for hamsters), when the dams should be
subjected to gross pathologic examination. Immediately after the dams are killed, fetuses should be delivered
by hysterotomy. Care should be taken to ensure that all fetuses (except those sacrificed before the end of the
study) are delivered at approximately the same stage of fetal development. The intact uterus should be
8. Maternal Toxicity and its Significance
9. Clinical Observation and Examination of Dams and Fetuses
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removed and weighed in order to calculate the adjusted body weight gain. The contents of the uterus should
then be examined for embryonic or fetal deaths and for the number of live fetuses. For dead fetuses, it is
usually possible to estimate and describe the approximate time of death in utero (early and late deaths). The
number of corpora lutea should be determined for all pregnant animals.
The uterus of each dam that does not appear to be pregnant should be stained in a solution of sodium or
ammonium sulfide(4) or other appropriate chemical to enhance the visibility of resorption sites. Evaluation of
the females during Cesarean sections and subsequent fetal analyses should be conducted blind in order to
minimize unconscious bias.
After removal from the uterus, the weight and sex of each fetus should be determined. The fetus should be
examined externally, and all deviations from normal should be noted. Additional end points may be measured,
such as the crown-to-rump distance of each fetus. The sex of rabbit fetuses should be determined by internal
examination. Each fetus should be weighed individually, and the mean fetal weight per sex per group should
be calculated.
Fetuses should be evaluated for skeletal and soft-tissue anomalies. For rodents, approximately one-half of the
rodent fetuses should be preserved in Bouin's solution and sectioned by the Wilson serial section technique to
evaluate alterations of the soft tissues. (9) The remaining fetuses should be prepared and stained for skeletal
anomalies (Alizarin red stain for bone and optional Alcian blue stain for cartilage). The assignment to soft-
tissue or skeletal examination should be done randomly or alternately. The alternation procedure is sometimes
not followed when an abnormality is found which would be better observed by a different technique. For
example, a specimen with an obvious skeletal defect would be prepared for skeletal examination. For
identification of rodent bones, the atlas of Yasuda and Yuki (10) may be consulted. Alternatively, all rodent
fetuses may be freshly dissected (1),(5) to discover soft-tissue abnormalities, then fixed and examined for
skeletal anomalies.
Each rabbit fetus should be examined for both soft-tissue and skeletal malformations and variations. The
bodies should be evaluated for soft-tissue anomalies by fresh dissection, followed by fixation and an
examination for skeletal anomalies. Internal head structures should be evaluated in at least one-half of the
fetal heads of rabbit fetuses. This evaluation should include at least the eyes, brain, nasal passages, and
tongue.
When a developmental toxicity study is performed as a stand-alone study, there is no need to perform
histopathology unless abnormalities are noted in the organs at the time of Cesarean section.
Because the maternal animal is treated during gestation rather than the developing organism, data should be
calculated as incidence per litter or as the number and percent of litters with particular end points. The degree
of maternal toxicity may be useful in assessing the relevance of any embryotoxicity or fetotoxicity observed in
the treated groups. Parameters used to measure maternal toxicity include body weight and adjusted body
weight, feed and fluid consumption, daily clinical observations, and necropsy data such as organ weights.
If treatment is given throughout gestation, implantation may be affected. If, however, treatment begins after
implantation, conception and implantation rates should be the same in control and treated groups. End points
to be measured per litter should include the number of implantations, corpora lutea, live fetuses (and with
separate sexes), dead fetuses, and resorbed fetuses. For litters with live fetuses, mean male and female body
weights and the incidence per litter of all divergences from normal fetal development (skeletal and visceral
analysis) should also be reported.
Values from control and test groups of animals should be compared statistically. The following techniques may
be used, but others may be substituted if they are appropriate. Maternal body weights may be compared by
analysis of co-variance after adjustment for initial body weight, and then analyzed by protected least
significant difference tests. Fetal body weights may be evaluated using nested analysis of variance. Anomalies
in litters may be compared by Fisher's exact test. Fetal survival and incidence of abnormalities per litter may
be compared by analysis of variance after the data have been transformed by use of the Freeman-Tukey arc-
sine transformation.
10. Histopathology
11. End Points Measured
12. Analysis of Data
D. Reporting the Results of Developmental Toxicity Studies
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/ucm078396.htm
Reports of all studies should contain the information required by the Good Laboratory Practice Regulations,
including a copy of the study protocol and all amendments, absolute values for all parameters, complete data
(individual pups) and tables of data summarized and analyzed by litter. Because the maternal animal is
treated during gestation rather than the developing organism, data should be calculated as incidence per litter
or as number and percent of litters with particular end points. The dosage rate of the test substance (doses)
should be reported as mg/kg/day (milligrams of test substance per kilogram of body weight per day).
Problems commonly encountered in the review of developmental toxicity studies include insufficient numbers
of pregnant animals per control or treatment group, non-random selection procedures, and statistical analyses
of data on a per-fetus basis instead of a per-litter basis. Careful consideration of recommended guidelines and
a review of protocols by the Agency before studies are conducted should help eliminate such problems.
Relevant historical control data may be used to increase the understanding of the study results. When used,
historical data should be compiled and presented in an appropriate manner with additional information, such
as dates of study, strain of animals, vehicle, and route of administration.
1. 	Barrow, M.V. and Taylor, W.J. (1969). A Rapid Method for Detecting Malformations in Rat Fetuses. J.
Morphol. 127:291-305.
2. 	Collins, T.F.X., Sprando, R.L., Hansen, D.L., Shackelford, M.E., and Welsh, J.J. (1998). Testing
Guidelines for Evaluation of Reproductive and Developmental Toxicity of Food Additives in Females. Int.
J. Toxicol. 17:299-325.
3. 	Institute of Laboratory Animal Resources. (1996). Guidelines for the Care and Use of Laboratory
Animals. National Academy Press, Washington, D. C.
4. 	Salewski (Koeln), V.E. (1964). Faerbermethode zum Makroskopischen Nachweis von Implantations
Stellen am Uterus der Ratte. Naunyn-Schmeidebergs Archiv Pharmakol. Exper. Pathol. 247:367.
5. 	Staples, R.E. (1977). Detection of Visceral Alterations in Mammalian Fetuses. Teratology 9:A37-A38.
6. 	U.S. Food and Drug Administration. (1978). Good Laboratory Practice Regulations for Nonclinical
Laboratory Studies. U.S. Code of Federal Regulations. Title 21 Part 8.
7. 	U.S. Food and Drug Administration. (1982). Toxicological Principles for the Safety Assessment of Direct
Food Additives and Color Additives Used in Food. U.S. Food and Drug Administration, Bureau of Foods,
Washington, DC.
8. 	U.S. Food and Drug Administration. (1993). Toxicological Principles for the Safety Assessment of Direct
Food Additives and Color Additives Used in Food, Redbook 2000 (Draft). U. S. Food and Drug
Administration, Center for Food Safety and Applied Nutrition, Washington, DC.
9. 	Wilson, J.G. (1965). Methods for Administering Agents and Detecting Malformations in Experimental
Animals. In Teratology Principles and Techniques (J.G. Wilson and J. Warkany, Eds.), pp. 262-277.
University of Chicago Press, Chicago.
10. 	Yasuda, M. and Yuki, T. (1996). Color Atlas of Fetal Skeleton of the Mouse, Rat, and Rabbit. Ace Art Co.,
Osaka, Japan.
IV. References
Links on this page:
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July 2000
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
1. 	Summary
2. 	Background
3. 	Evaluating Neurotoxicity
A. 	Screening
1. 	Elements of a Neurotoxicity Screen
2. 	Considerations in Protocol Design for Neurotoxicity Screening
B. 	Special Neurotoxicity Testing
1. 	Characterization of Effects
2. 	Dose-Response Relationships
4. 	References
This chapter defines neurotoxicity and the broad spectrum of adverse effects to the nervous system that may
occur in the adult and developing organism. Emphasis is placed on the need to effectively minimize the risk of
human neurotoxicity by assessing the neurotoxic potential of food ingredients. The chapter proceeds with
explicating the nature and extent of information needed for an assessment of neurotoxic potential and
suggests a strategy for obtaining this information as a routine part of the toxicological testing to evaluate the
safety of chemicals proposed for use as food ingredients. Consistent with the basic strategy advocated by FDA
for toxicological testing, the assessment of neurotoxic potential would be most effectively carried out through
a structured process of tiered testing in which chemicals are initially screened for signs of neurotoxicity as part
of those toxicity studies recommended for entrance-level testing of proposed food ingredients . Chemicals
identified as possible neurotoxicants become candidates for subsequent special neurotoxicity testing designed
to confirm and characterize the scope of nervous system involvement and to determine dose-response
characteristics, including a quantitative determination of the no-observed-adverse-effect level. The basic
elements of a neurotoxicity screen and of special neurotoxicity testing are presented and the principle points
Redbook 2000: IV.C.10 Neurotoxicity Studies
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter IV.C.10. Neurotoxicity Studies
I. Summary
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
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to consider in protocol design are discussed.
The nervous system regulates and maintains diverse biological processes that are essential not only for
survival but also for maintaining an acceptable quality of life. The proper functioning of the nervous system
enables an organism to receive information from its internal and external environments and to orchestrate
appropriate adaptive physiological and behavioral responses. An extensive body of data demonstrates that
diverse chemical substances can alter the structure and function of the nervous system in a variety of ways
with notable human health consequences(1) . Alterations that significantly compromise an organism's ability to
function appropriately in its environment are considered adverse. Neurotoxicity refers to any adverse effects
of exposure to chemical, biological or physical agents on the structure or functional integrity of the developing
or adult nervous system. Neurotoxic effects may involve a spectrum of biochemical, morphological,
behavioral, and physiological abnormalities whose onset can vary from immediate to delayed following
exposure to a toxic substance, and whose duration may be transient or persistent. Depending upon their
severity, some of these abnormalities may have life-threatening consequences; more commonly, they result
in diminished quality of life. Neurotoxicity may result from effects of the toxic substance acting directly on the
elements of the nervous system or acting on other biological systems which then adversely affect the nervous
system. From a safety standpoint neurotoxic effects resulting from either a direct or indirect action of a
chemical on the nervous system are important components of a chemical's toxicological profile. However, in
those instances where neurotoxicity occurs secondary to some non-nervous system toxicity, the latter would
typically represent the more sensitive endpoint.
In 1982, the FDA issued guidelines for toxicological testing of food ingredients (2) . Although neurotoxicity was
neither explicitly discussed nor defined in these guidelines, there were certain elements included in the
conventional toxicity studies which have traditionally been used to assess nervous system toxicity. In general,
these included a routine pathological evaluation of neuronal tissue and cage-side observations for clinical signs
of toxicity. In 1985, FDA commissioned the Federation of American Societies for Experimental Biology (FASEB)
to assess the utility of these current FDA guidelines for detecting neurotoxic hazards. (3) One conclusion of the
FASEB report was that the current guidelines are too broad and nonspecific with respect to the nature and
extent of information which needs to be provided to the FDA for an evaluation of a chemical's neurotoxic
potential. The limited information derived from conventional toxicity screening studies, as currently conducted
and reported, enables little more than the detection of clearly evident nervous system toxicity associated with
general neuropathology and overt neurological dysfunction. Little consistent or systematically documented
information is typically available about other possibly less severe, but equally important, types of neurotoxic
effects including, for example, behavioral and physiological dysfunction and developmental neurotoxicity.
Incomplete documentation about the range of adverse effects to the structural and functional integrity of the
nervous system limits the effective evaluation of the full spectrum of neurotoxic hazards. (4) The present FDA
guidelines are intended to explicate more clearly the nature and extent of information deemed necessary for
the assessment of neurotoxic potential and to suggest a strategy for obtaining this information as part of the
safety evaluation process.
Until recently, neurotoxicity was equated with neuropathy involving frank neuropathological lesions or overt
neurological dysfunctions, such as seizure, paralysis or tremor. Examples of chemically induced neuropathy in
humans (for example, from exposure to domoic acid, lead, organic mercury, hexane, carbon disulfide, and tri-
ortho-cresylphosphate) emphasize the need for assessing the neurotoxic potential of chemicals to which
humans may be exposed.(5) Although neuropathy is appropriately recognized as a manifestation of
neurotoxicity, it is now clear that there are numerous other endpoints which may signal nervous system
toxicity. (6) Ongoing research on nervous system toxicity continues to reveal the diversity of biochemical,
structural, and functional abnormalities that toxicants can elicit, both directly and indirectly.(7) Neurotoxic
chemicals invariably initiate their effects at the molecular level, altering cellular neurochemical processes. The
qualitative nature of these alterations or their magnitude may be such as to result in cytoarchitectural changes
and neuropathological effects accompanied by nervous system dysfunction expressed as physiological or
behavioral abnormalities. (8) Motor incoordination, sensory deficits, learning and memory impairment, changes
in emotion, and altered states of arousal in the adult and the developing organism are examples of deficits
recognized as functional indices of possible neurotoxicity. Notably, physiological or behavioral dysfunctions
may occur prior to, or even in the absence of, evident neuropathology or other signs of toxicity.(9) This is
exemplified by the behavioral dysfunctions associated with exposure to such neuroactive chemicals as
barbiturates, amphetamines, ethanol, lead, and carbon monoxide at exposure levels that elicit little or no
II. Background
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apparent signs of neuropathy.(10) This dissociation of neuropathology and functional changes may involve a
number of factors, including the intrinsic toxicity of a chemical and, particularly, the dose and regimen of
exposure. Continued reliance on neuropathy as the primary criterion of neurotoxicity is overly simplistic and
does not adequately reflect contemporary concerns about the broader spectrum of potential neurotoxic effects
on the adult and developing organism.
Among the various approaches that can be used for assessing neurotoxicity, behavioral testing in conjunction
with neuropathological evaluation represent a practical means of obtaining a relatively comprehensive
assessment of the functional development and integrity of the nervous system within the context of a
standard toxicity study. (11) Behavior is an adaptive response of an organism, orchestrated by the nervous
system, to some set of internal and external stimuli. A behavioral response represents the integrated end
product of multiple neuronal subsystems including sensory, motor, cognitive, attentional, and integrative
components, as well as an array of physiological functions.(12) As such, behavior can serve as a measurable
index of the status of multiple functional components of the nervous system. Since behavioral testing is non-
invasive, it can be applied repeatedly for longitudinal assessment of the neurotoxicity of a test compound,
including persistent or delayed treatment-related effects.(13) Furthermore, since neuronal function can be
influenced by the status of other organ systems in the body (e.g., cardiovascular, endocrine, and immunologic
systems), certain types of behavioral changes may indirectly reflect significant primary toxicity in other organ
systems. For this reason it is important to emphasize that the assessment of neurotoxicity necessitates an
integrated interpretation of all toxicologic data.
Behavioral testing has been established as a reliable toxicological index in safety assessment. Considerable
progress has been made in the standardization and validation of neurobehavioral and neurodevelopmental
testing procedures.(14) As a result, a variety of behavioral methodologies is available for use in determining
the potential of chemical substances to affect adversely the functional integrity of the nervous system in adult
and developing organisms. (15) Behavioral testing can be readily incorporated into toxicity testing protocols
and, together with neuropathological evaluation, can enhance the ability to assess neurotoxic hazard (16) .
Because of the impact that nervous system toxicity can have on human health, assessing the neurotoxic
potential of a chemical proposed for use as a food ingredient should be an essential element in that chemical's
toxicological profile. (17) Current scientific technology provides ample means of effectively assessing neurotoxic
potential of chemical substances (18) . To effectively minimize the risk of potential neurotoxicity in humans, it is
important that the best available science be used to develop the necessary information. It should be clear that
neurotoxic effects identified in experimental animal models may not always compare exactly with what may
occur in humans. Nonetheless, these effects are still interpreted as being indicative of treatment related
effects on the nervous system and predictive of possible adverse health effects in humans. As advances in the
neurosciences continue to evolve, our understanding of the processes underlying neurotoxicity will become
increasingly clear. This will enhance our ability to assess neurotoxicity in a manner that is more predictive of
potential human risk and to apply the available neurotoxicological information more reliably in support of
regulatory decisions. (19)
The reliability of assessing the full spectrum of neurotoxic potential for a test substance is directly related to
the extent to which the detection and evaluation of neurotoxicity is explicitly included as a specific, defined
objective of routine toxicity testing. (20) Consistent with the basic strategy advocated by the FDA for
toxicological testing and with the recommendations by expert committees, scientific panels and health-related
organizations, the assessment of neurotoxic potential is most efficiently carried out through a structured
process of tiered testing.(21) Each stage of testing would focus on different aspects of assessment. In the first
stage of testing chemicals would be initially screened across a range of dose levels for any clinical or
pathological signs of toxicity, including those involving the nervous system. Those chemicals showing evidence
of adversely affecting the nervous system may be presumptively identified as candidates for subsequent
specific neurotoxicity testing to confirm and further characterize the scope of nervous system involvement
(i.e., characterization of effects) and to determine dose-response kinetics (i.e., dose-response determination),
including a quantitative determination of the no-observed-adverse-effect level (NOAEL).
A tiered approach to neurotoxicity testing and evaluation allows for multiple decision points at which
scientifically based decisions can be made about the adequacy of available information and the need for
additional testing. To facilitate such decisions, specific summary statements regarding the neurotoxic potential
III. Evaluating Neurotoxicity
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of the test compound should be included in the evaluation of the results of each level of testing. Since the
nervous system interacts dynamically with certain other organ systems in the body, adverse effects to the
nervous system should be evaluated within the context of a comprehensive assessment of all significant toxic
effects for a test compound. In this regard, the neurotoxicity summary statements should reflect an integrated
assessment of all relevant toxicology data which are available. This would include information derived not only
from tests specifically focused on the detection of nervous system toxicity (e.g., neuropathology, behavioral
dysfunctions, neurochemical alterations or physiological changes), but also from more conventional
toxicological testing that focuses on other measures of toxicity, for example, general organ pathology and
adverse changes in growth, development, food or water intake, or endocrine status.
The neurobiological implications of some conventional endpoints of toxicity are certainly more evident than
others. For example, a compound that induces specific teratogenicity of the nervous system, even at high
dose levels, would be suspect for adversely affecting the development of nervous system function at lower
doses. The neurotoxicological significance of other types of toxicity, however, may be less obvious. For
instance, chemicals found to alter hormonal balance might also be suspected of affecting the structural or
functional integrity of the nervous system, since endocrine status and the nervous system are interrelated.
Altered growth, which is considered an index of general toxicity, may also signal the presence of neurotoxicity.
In the developing organism, abnormal growth may reflect a treatment related neurotoxicity of the mother
involving poor care of the nursing offspring. In the adult, altered growth stemming from changes in food or
water intake may reflect underlying nervous system dysfunction, since both eating and drinking are
consummatory behaviors with neuromuscular and physiological components under neuronal control. It should
be clear, however, that such generic toxicological endpoints, by themselves, are not to be taken as evidence
of neurotoxicity. Rather, when viewed in conjunction with other available data, such effects may serve to
indicate the possibility of treatment related effects on the nervous system. Again, it is important to emphasize
the need for integrated interpretation of all available toxicological data in the process of assessing neurotoxic
potential.
The first stage in assessing neurotoxicity involves a process of screening to identify those chemicals that
exhibit any potential for adversely affecting the nervous system. It should be clear that the primary objective
of screening is detection. Chemicals identified as exhibiting a significant potential for neurotoxicity would
typically be considered as a possible candidate for additional more specific neurotoxicity testing. Under such
conditions, the nature and extent of information which is typically developed by screening methods would not
provide a sufficient basis for determining the NOAEL for neurotoxicity. Rather, additional more specific
neurotoxicity information developed in subsequent stages of testing would be needed to accurately determine
the NOAEL. If significant neurotoxic potential is not identified in screening, then there would typically be
neither a basis nor a need to define a NOAEL for neurotoxicity.
There are basically three sources of neurotoxicity screening information. One involves the use of structure
activity relationships (SAR), the second relies on published literature and other sources of documentation, and
the third involves empirical testing. The usefulness and reliability of SAR for identifying potential
neurotoxicants is, at the present time, rather limited due to the fact that SAR databases for neurotoxicity are
still being developed. The use of published literature or other types of documented information, to the extent
that this type of information is available and appropriate for regulatory application, can be of significant value
in identifying chemicals that may affect the nervous system. However, this type of information is usually
scattered and typically not available for many food ingredients. At the present time, the primary means of
obtaining neurotoxicity screening data is through empirical testing. The experimental data needed to screen
chemicals for potential neurotoxicity should be routinely obtained as part of those toxicity studies
recommended for "entrance-level" testing of proposed food ingredients. Neurotoxicity screening information
could be developed most appropriately in short-term (e.g., 14 to 28-day rodent and non-rodent) studies to
screen adult animals exposed to the test chemical across a range of relatively high doses for brief periods of
time, in subchronic (e.g., 90-day rodent and non-rodent) and long-term (e.g., one-year non-rodent) studies
to screen adult animals following more prolonged exposure across a range of relatively lower doses, and
reproduction/developmental studies to screen for potential developmental neurotoxicity in perinatally exposed
offspring. The development of neurotoxicity screening information in other types of toxicity studies (e.g.,
chronic studies) would certainly be acceptable and encouraged.
Screening for neurotoxicity involves the use of valid, cost-effective procedures which can be carried out
rapidly and routinely on large numbers of chemicals to detect the presence or absence of immediate or
A. Screening
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delayed adverse effects on the nervous system.(22) Neurotoxicity can appear as a wide range of morphological
and functional abnormalities involving the nervous system at very specific or multiple levels of its
organization. (23) Under the previous guidelines for toxicity testing of proposed food ingredients the
identification of neurotoxic effects was based on information derived from a general pathological evaluation of
a few sections of neuronal tissue and an unstructured casual observation of test animals in their cages for
overt signs of toxicity.(24) This approach focused detection on the more severe forms of neurotoxicity. To
maximize the scope of detection, screening should be sufficiently comprehensive to enable the detection of a
representative variety of pathological changes and functional disorders of the peripheral, central and
autonomic segments of the nervous system.(25) In reproduction/developmental studies, age-appropriate
neurotoxicity screening should enable the detection of treatment-related effects on the physical and functional
development of the offspring.
The elements of a basic neurotoxicity screen should include a specific histopathological examination, in
conjunction with a systematic clinical evaluation.
z Specific histopathological examination
A specific histopathological examination should be made of tissue samples representative of all major
areas and elements of the brain, spinal cord and peripheral nervous system. Emphasis should be placed
more on the carefulness of the histopathological examination of the neuronal tissue and the
documentation of findings rather than on the numbers of sections used, provided that all major areas
and elements of the nervous system are included. For purposes of screening, either immersion fixation
or in situ perfusion of tissues is acceptable. Typically, the initial examination may be carried out on
tissues from the control and the highest dose group. Positive findings would then be followed by
examination of tissues from the other dose groups. The concept of age-appropriateness should also be
considered in the morphological evaluation of the immature nervous system.(26)
z Systematic clinical evaluation
A systematic clinical evaluation of experimental animals should be conducted inside and outside of their
cages using a clearly defined battery of clinical tests and observations selected to detect signs of
significant neurological disorders, behavioral abnormalities, physiological dysfunctions, and any other
signs of nervous system toxicity. Typically, in addition to the animal's physical appearance, body posture
and weight, the clinical screen should provide sufficient information to assess the incidence and severity
of such endpoints as seizure, tremor, paralysis or other signs of neurological disorder; the level of motor
activity and alertness; the animals' reactivity to handling or other stimuli; motor coordination and
strength; gait; sensorimotor response to primary sensory stimuli; excessive lacrimation or salivation;
piloerection; diarrhea; polyuria; ptosis; abnormal consummatory behavior; and any other signs of
abnormal behavior or nervous system toxicity. To accommodate age-appropriate testing, screening for
potential developmental neurotoxicity could include measures of postnatal development of
representative physical landmarks (for example, body weight and development of external genitalia) and
functional milestones (for example, righting reflex, startle response, and motor development) in the
experimental offspring. In carrying out the functional evaluation screen, animals should be initially
observed in their home cages and then removed to an open arena for the completion of the observations
and manipulative testing. As appropriate, more sensitive and objective indices of neurotoxicity, such as
tests of learning and memory, and quantitative measures of sensory function and motor behavior, could
be included as part of the screen. (27) Further, it is important that the neurotoxicity screening information
be supplemented with any other relevant toxicological findings.
There are a number of available publications to guide in the design and conduct of neurotoxicity screens
appropriate for the adult organism(28) and for the developing and adult offspring.(29) The process of protocol
design for deriving neurotoxicity screening information should include consideration of the following:
z Each testing laboratory should develop and maintain an historical database demonstrating its continuing
competence in the assessment of neurotoxicity. The neurotoxicity screen should consist of valid test
1. Elements of a Neurotoxicity Screen
2. Considerations in Protocol Design for Neurotoxicity Screening
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methodology administered by personnel who, in compliance with GLP requirements, are adequately
trained to conduct the procedures appropriately. The reliability and sensitivity of the proposed screening
to be used for detecting neurotoxic effects should be documented by the availability of historical or
concurrent positive control data.
z To help ensure the complete and consistent application of the neurotoxicity screen throughout a
particular study, each study protocol should include a detailed description of the particular screen to be
used in that study, including its composition, the test procedures to be followed, the time periods at
which the screen is to be carried out, the neuronal structures to be examined, the endpoints to be used,
and the methods for recording and analyzing the data. During the conduct of the studies, the detailed
clinical evaluation should be carried out systematically, using a prepared checklist of tests and
observations when appropriate. All experimental procedures should be documented.
z Since neurotoxicity screening is intended to be a routine part of both general and reproductive toxicity
studies, the specific composition of the screen and the endpoints to be recorded should be consistent
with the particular focus of the study and, specifically, be appropriate for the age (and species) of the
animals to be tested. For example, to screen for potential developmental neurotoxicity, it would be
appropriate for a systematic evaluation to be carried out on representative male and female offspring
from each experimental litter in reproduction studies and to include measures of the ontogenetic
development and maturation of representative physical landmarks (for example, body weight and
development of external genitalia) and functional milestones (for example, righting reflex, startle
response, and motor development) in those offspring. The evaluation of offspring during the preweaning
period should be planned so as to maintain the integrity of the primary reproductive study, for example
by minimizing the period of pup separation from the dams. The optional inclusion of other, more
sensitive, or more objective indices of neurotoxicity, such as tests of learning/memory and quantitative
measures of sensory and motor function, to supplement the basic screening of the developing and/or
mature offspring would be encouraged in separate or satellite litters. The concept of age-appropriateness
should also be considered in the morphological evaluation of the immature nervous system.(30) There
are a number of available publications to guide the design and conduct of clinical testing appropriate for
neurotoxicity screening of the adult organism(31) and for developing and adult offspring. (32)
z Testing should be carried out at representative intervals throughout the duration of the study (including,
when feasible, a pretreatment baseline) to provide information about the consistency of the neurotoxic
effect(s), and, as possible, about their onset, duration and reversibility.
z At the discretion of the sponsor or testing laboratory, satellite groups of animals could be used to carry
out the neurotoxicity screen testing.
z A sufficient number of male and female animals from each experimental and control group should be
used (as recommended in the guidelines for the primary toxicity protocols) to ensure valid statistical
analyses giving consideration to the variability of the endpoints being measured. As possible, the
selection of tests should afford the best level of detectability with use of the smallest number of animals.
In adult studies the individual animal is routinely used as the statistical unit, whereas in developmental
studies the litter is typically considered to be the appropriate statistical unit. For screening purposes, the
initial histochemical examination could involve tissues from control and high dose animals. If treatment-
related effects are found, the subsequent examination of tissues from the lower dose groups would be
warranted.
z The experimental design should include measures to minimize inadvertent bias, for example by using
random assignment to treatment groups and, as feasible, carrying out testing with the experimenters
blind to treatment conditions. Appropriate procedures should be followed to control for potentially
confounding variables, such as housing conditions, diet and nutritional status, circadian cycles, test to
test interactions, environmental conditions, and handling. For example, in the process of screening for
potential developmental neurotoxicity the direct clinical evaluation of the pregnant or lactating dams
should be limited to minimize influence of such handling on maternal behavior.
z To take full advantage of the neurotoxicity screening information routinely developed in toxicological
testing, experimental data should be accurately recorded, documented and reported to the FDA.
Summary tables of all positive effects should be presented. In addition, all data collected (positive and
negative) should be submitted to the FDA to enable review personnel the opportunity of examining the
actual study results. As appropriate, data should be analyzed using suitable and acceptable statistical
procedures. This information, together with any other pertinent toxicity data, should be incorporated into
an integrated assessment of the potential for the test chemical to adversely affect the structural or
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functional integrity of the nervous system. Based on this assessment, an explicit statement should be
made as to whether or not the test chemical represents a potential neurotoxic hazard which may require
special neurotoxicity testing. Study protocols for additional neurotoxicity testing should be developed
using valid state-of-the-art methodology.
z Throughout the process of protocol design and testing in the assessment of neurotoxic potential, the
opportunity for consultation with FDA is available and encouraged.
Increasing attention is being devoted to the development of in vitro systems for assessing the
neurotoxicological impact of chemical agents. (33) In vitro methods would have practical advantages, such as
minimizing the use of live animals, but validation studies remain to be done to correlate in vitro results with
neurotoxicological responses in whole animals. Such systems, once appropriately validated, may have
particularly useful application in screening for potential neurotoxicity and in helping to elucidate mode of
action or mechanistic information.
The information collected during screening is used to determine whether or not the test chemical represents a
potential neurotoxic hazard and whether additional tests to confirm and characterize the neurotoxicity, to
define NOAELs, and to develop other necessary information should be recommended. A number of
considerations enter into the scientific interpretation of the neurotoxicity screening information when making
this evaluation. These include the adequacy and completeness of the screening assessment; the nature and
severity of the effects detected; consistency of effects across dose; consistency of effects across testing
intervals within a study; replicability of effects across different types of toxicity studies; presence of other
toxic effects; and the margin of difference between the doses producing neurotoxicity and those producing
other toxic effects. The extent to which screening provides the information to address these issues adds to the
level of confidence in identifying a potential neurotoxic hazard and aids in determining the need to proceed
from screening to the development of more comprehensive neurotoxicity information. The decision to proceed
with such specialized neurotoxicity testing should be made in consultation with the FDA.
When a chemical is presumptively identified by SAR, empirical screening, or other sources of information as
producing neurotoxicity, that chemical becomes a candidate for additional neurotoxicity testing. Chemicals not
identified as having neurotoxic effects during screening will generally not be recommended for subsequent
neurotoxicity testing, although exceptions may occur. Special neurotoxicity testing focuses on the
characterization of the neurotoxic effects and the determination of dose-response relationships:
Following the presumptive identification of chemicals that adversely affect the nervous system, the next level
of testing focuses attention on determining the nature and extent to which the nervous system is affected by
that chemical (characterization). At this level the neurotoxic effects found during screening are further
characterized and studies are conducted to determine whether the test chemical has any other, possibly more
subtle, effects on the structural and functional integrity of the nervous system in mature and developing
organisms. The in-depth assessment of neurotoxicity at this stage of testing should include information about
the nature and severity of effects, the temporal pattern of onset of effects (particularly when delayed
neurotoxicity occurs), and the duration of effects. To enhance detection of subtle neuropathological findings,
tissues should be perfusion-fixed in situ and a detailed histopathological examination (more thorough than the
histopathology examination performed during screening) should be carried out involving the use of special
stains to highlight relevant neural structures.(34)
The neurofunctional assessment at this level should routinely include a core battery of behavioral and
physiological tests designed to detect adverse changes to the primary subfunctions (e.g., cognitive, sensory,
motor, and autonomic) of the nervous system in the mature and developing nervous system.(35) The need for
additional special tests may logically follow from information obtained during screening; for example, if a
chemical is observed to induce convulsions during screening, the seizure potential and pro-convulsant
properties of that chemical should be more specifically characterized during the second level of testing.
B. Special Neurotoxicity Testing
1. Characterization of Effects
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A critical element used in defining a chemical's neurotoxic hazard is the no-observed-adverse-effect level
(NOAEL), typically using the most relevant and sensitive endpoint identified in previous testing. To enable a
more quantitative determination of the NOAEL, ample data should be obtained to thoroughly characterize the
dose-response and dose-time relationships in repeated exposure studies, e.g., intermittent and continuous
exposure regimes, typically using the most relevant and sensitive endpoint.
The protocols for special neurotoxicity testing, which should be designed in consultation with FDA, should take
into consideration elements similar to those involved in the development of protocols for neurotoxicity
screening, including the appropriateness and reliability of the test procedures, the suitability of the control
measures, and the adequacy of the experimental design and schedule of testing (frequency and duration).
Consistent with the guidelines for the primary toxicity testing protocols, special neurotoxicity testing would
initially be carried out using rodents as the principal species of choice. However, as appropriate and in
consultation with FDA, neurotoxicity studies using non-rodent species may be recommended, on a case-by-
case basis, to develop information needed for more reliable cross-species extrapolation of data.(36)
At the stage of special neurotoxicity testing, efforts to develop additional relevant information for a more
comprehensive assessment of neurotoxic hazard are certainly encouraged. For example, information regarding
the occurrence of treatment-related neurochemical changes, the pharmacokinetic properties of the test
compound, or the factors that may modulate the sensitivity of the organism to the test compound could
contribute to a better understanding of the neurobiological processes underlying the chemically induced
neurotoxicity. This mechanistic type of information would enable a more reliable interpretation of the available
animal data for predicting neurotoxic risk in humans.
1. 	U.S. Congress, Office of Technology Assessment (1990) (42) 	(Return to text)
2. 	U.S. Food and Drug Administration (1982)(47) 	(Return to text)
3. 	Federation of American Societies for Experimental Biology Report (1986) (8) ; Leukroth (1987)(16)
(Return to text)
4. 	McMillan (1987) (19) ; U.S. Office of Technology Assessment (1990) (42) ; Vorhees (1987) (49) 	(Return to
text)
5. 	Spencer and Schaumburg (1980)(37) ; U.S. Office of Technology Assessment Report (1990) (42) ; World
Health Organization Report (1986) (54) 	(Return to text)
6. 	Tilson (1987)(38) 	(Return to text)
7. 	Buelke-Sam et al. (1985) (3) ; Federation of American Societies for Experimental Biology Report (1986)
(8) ; Leukroth (1987) (16) ; Reiter (1987) (30) ; Spencer and Schaumburg (1980) (37) ; World Health
Organization Report (1986)(54) 	(Return to text)
8. 	Anger and Johnson (1985) (1) ; Federation of American Societies for Experimental Biology Report (1986)
(8) ; Leukroth (1987) (16) ; Reiter (1987) (30) ; Spencer and Schaumburg (1980) (37) 	(Return to text)
9. 	Federation of American Societies for Experimental Biology Report (1986) (8) ; Reiter (1987) (30) ; Riley
and Vorhees (1986)(31) ; World Health Organization Report (1986)(54) 	(Return to text)
10. 	Hutchings et al. (1987)(14) 	(Return to text)
11. 	Federation of American Societies of Experimental Biology Report (1986) (8) ; Vorhees et al. (1984) (50)
(Return to text)
12. 	Mitchell and Tilson (1982) (20) 	(Return to text)
13. 	Leukroth (1987) (16) 	(Return to text)
14. 	Buelke-Sam et al. (1985) (3) ; Federation of American Societies of Experimental Biology report (1986) (8) ;
Leukroth (1987) (16) ; Moser (1997) (21) ; Rees et al. (1990)(29) ; U.S. EPA report (1985) (43) ; U.S. EPA
report (1991)(45) ; Weiss and O'Donoghue (1994)(52) ; World Health Organization report (1986) (54)
(Return to text)
15. 	Leukroth (1987) (16) 	(Return to text)
16. 	Eisenbrandt et al. (1994)(7) ; Mattsson et al. (1990)(18) 	(Return to text)
17. 	Leukroth (1987) (16) ; National Academy of Sciences report (1982) (24) ; Reiter (1987) (30) ; Sobotka
2. Dose-Response Relationships
Endnotes
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(1986) (35) ; U.S. Office of Technology Assessment report (1990)(42) 	(Return to text)
18. 	Chang (1994)(4) ; Chang and Slikker (1995) (5) ; Moser (1997) (21) ; Tilson and Mitchell (1992) (39) ; U.S.
EPA report (1994) (46) ; WHO (1986) (54) 	(Return to text)
19. 	Reiter (1987)(30) ; U.S. Committee on Science and Technology report (1986)(48) 	(Return to text)
20. 	Federation of American Societies of Experimental Biology report (1986)(8) ; Sobotka (1986) (35)
(Return to text)
21. 	Federation of American Societies of Experimental Biology report (1986)(8) ; National Academy of
Sciences report (1975)(23) ; National Academy of Sciences report (1982) (24) ; U.S. FDA report (1982)(47) ;
World Health Organization report (1986) (54) 	(Return to text)
22. 	Mitchell and Tilson (1982) (20) ; Moser (1997)(21) 	(Return to text)
23. 	Anger and Johnson (1985) (1) ; Leukroth (1987)(16) ; Reiter (1987) (30) ; Spencer and Schaumburg (1980)
(37) ; Tilson and Mitchell (1992) (39) 	(Return to text)
24. 	U.S. FDA report (1982)(47) 	(Return to text)
25. 	Federation of the American Societies of Experimental Biology report (1986)(8) ; Nelson (1991) (25)
(Return to text)
26. 	Rodier (1990)(32) 	(Return to text)
27. 	National Academy of Sciences report (1982) (24) ; U.S. EPA report (1985)(43) ; U.S. FDA report (1982)
(47) ; World Health Organization report (1986) (54) 	(Return to text)
28. 	Broxup (1991)(2) ; Buelke-Sam et al. (1985)(3) ; Chang (1994) (4) ; Chang and Slikker (1995) (5) ; Deuel
(1977) (6) ; Fox (1968)(9) ; Gad (1982) (10) ; Gad (1989) (11) ; Krinke (1989) (15) ; Leukroth (1987) (16) ;
Marshall et al. (1971)(17) ; Moser et al. (1988) (22) ; Moser (1997)(21) ; National Academy of Sciences
report (1982)(24) ; Nelson (1991) (25) ; O'Donoghue (1989) (26) ; Paule (1990)(27) ; Paule et al. (1988)(28) ;
Schultz and Boysen (1991)(33) ; Spencer et al. (1980)(36) ; Tilson and Mitchell (1992) (39) ; Tilson and
Moser (1992)(40) ; Tupper and Wallace (1980)(41) ; U.S. EPA report (1985) (43) ; U.S. EPA (1988)(44) ; U.S.
EPA report (1991) (45) ; U.S. EPA report (1994) (46) ; U.S. Office of Technology Assessment report (1990)
(42) ; Vorhees (1987) (49) ; Wier et al. (1989)(53) ; World Health Organization report (1986) (54) 	(Return
to text)
29. 	Buelke-Sam et al. (1985) (3) ; National Academy of Sciences report (1982)(24) ; Nelson (1991) (25) ; Rees
et al. (1990)(29) ; Rodier (1990)(32) ; Slikker and Chang (1998) (34) ; U.S. EPA report (1985) (43) ; U.S. EPA
report (1988)(44) ; U.S.EPA report (1991)(45) ; U.S. FDA report (1982)(47) ; Vorhees (1987)(49) ; Vorhees
et al. (1979)(51) ; Vorhees et al. (1984)(50) ; World Health Organization report (1986) (54) 	(Return to
text)
30. 	Rodier (1990)(32) 	(Return to text)
31. 	Broxup (1991)(2) ; Buelke-Sam et al. (1985)(3) ; Chang (1994) (4) ; Chang and Slikker (1995) (5) ; Deuel
(1977) (6) ; Fox (1968)(9) ; Gad (1982) (10) ; Gad (1989) (11) ; Krinke (1989) (15) ; Leukroth (1987) (16) ;
Marshall et al. (1971)(17) ; Moser (1997)(21) ; Moser (1988) et al. (22) ; National Academy of Sciences
report (1982)(24) ; Nelson (1991) (25) ; O'Donoghue (1989) (26) ; Paule (1990)(27) ; Paule et al. (1988)(28) ;
Schultz and Boysen (1991)(33) ; Spencer et al. (1980)(36) ; Tilson and Mitchell (1992) (39) ; Tilson and
Moser (1992)(40) ; Tupper and Wallace (1980)(41) ; U.S. EPA report (1985) (43) ; U.S. EPA (1988)(44) ; U.S.
EPA report (1991) (45) ; U.S. EPA report (1994) (46) ; U.S. Office of Technology Assessment report (1990)
(42) ; Vorhees (1987) (49) ; Wier et al. (1989)(53) ; World Health Organization report (1986) (54) 	(Return
to text)
32. 	Buelke-Sam et al. (1985) (3) ; National Academy of Sciences report (1982)(24) ; Nelson (1991) (25) ; Rees
et al. (1990)(29) ; Rodier (1990)(32) ; Slikker and Chang (1998) (34) ; U.S. EPA report (1985) (43) ; U.S. EPA
report (1988)(44) ; U.S. EPA report (1991) (45) ; U.S. FDA report (1982) (47) ; Vorhees (1987) (49) ; Vorhees
et al. (1979)(51) ; Vorhees et al. (1984)(50) ; World Health Organization report (1986) (54) 	(Return to
text)
33. 	Harry et al. (1998)(13) ; U.S. Congress, Office of Technology Assessment (1990)(42) ; U.S. EPA report
(1994) (46) 	(Return to text)
34. 	Chang and Slikker (1995)(5) ; Spencer et al. (1980) (36) ; U.S. EPA report (1985) (43) ; U.S. EPA report
(1991) (45) ; World Health Organization report (1986) (54) 	(Return to text)
35. 	Geller et al. (1980)(12) ; Leukroth (1987) (16) ; U.S. EPA report (1985) (43) ; U.S. EPA report (1991) (45) ;
U.S. Office of Technology Assessment report (1990)(42) ; Vorhees et al. (1979)(51) ; Wier et al. (1989)
(53) ; World Health Organization report (1986) (54) 	(Return to text)
36. 	Fox (1968)(9) ; Paule (1990)(27) ; Paule et al. (1988) (28) 	(Return to text)
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1. 	Anger, W.K. and Johnson, B.L. (1985) Chemicals affecting behavior. In, Neurotoxicity of Industrial and
Commercial Chemicals. (J.L. O'Donoghue ed.) CRC Press. Boca Raton, FL. Vol. 1:51-148.
2. 	Broxup, B. (1991) Neuropathology as a screen for neurotoxicity assessment. Journal of the American
College of Toxicology, 10:689-695.
3. 	Buelke-Sam, J., Kimmel, C.A. and Adams, J. eds. (1985) Design considerations in screening for
behavioral teratogens: Results of the collaborative behavioral teratology study. In, Neurobehavioral
Toxicology and Teratology. Conference Proceedings 7(6):537-789.
4. 	Chang, L.W. (ed.) (1994) Principles of Neurotoxicology. Marcel Dekker, Inc.: New York.
5. 	Chang, L.W. and Slikker, W. Jr. (eds) (1995) Neurotoxicology: Approaches and Methods. Academic
Press Inc.: San Diego.
6. 	Deuel, R.K. (1977) Determining sensory deficits in animals. In, Methods in psychobiology. (R. Myers,
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7. 	Eisenbrandt, D.L., Allen, S.L., Berry, P.H., Classen, W., Bury, D., Mellert, W., Millischer, R.J., Schuh, W.
and Bontinck, W.J. (1994) Evaluation of the neurotoxic potential of chemicals in animals. Food Chemical
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9:691-704.
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neurotoxicology. J. Am. College Toxicol. 8:21-27.
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substances on behavior and neuromotor function: Conference Proceedings. NTIS Report No. ISBN-O-
916086-02-2.
13. 	Harry, G.J., Billingsley, M., Ruinink, A., Campbell, I.L., Classen, W., Dorman, D.C., Galli, C., Ray, D.,
Smith, R.A. and Tilson, H.A. (1998) In Vitro techniques for the assessment of neurotoxicity.
Environmental Health Perspectives, 106(Suppl 1):131-158.
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dysfunction from preclinical toxicologic data, Symposium Introduction. Neurotoxicology and Teratology,
9:397-401.
15. 	Krinke, G. (1989) Neuropathological screening in rodent and other species. Journal of the American
College of Toxicology, 8:141-146.
16. 	Leukroth, R.W. (1987) Predicting neurotoxicity and behavioral dysfunction from preclinical toxicologic
data. Neurotoxicology and Teratology 9:395-471.
17. 	Marshall, J.F., Turner, B.H. and Teitelbaum, P. (1971) Sensory neglect produced by lateral hypothalamic
damage. Science 174:523-525.
18. 	Mattsson, J.L., Eisenbrandt, D.L. and Albee, R. (1990) Screening for neurotoxicity: complimentarity of
functional and morphological techniques. Toxicologic Pathology 18:115-127.
19. 	McMillan, D.E. (1987) Risk assessment for neurobehavioral toxicity. Environ, Health Perspect. 76:155-
161.
20. 	Mitchell, C.L. and Tilson, H.A. (1982) Behavioral toxicology in risk assessment: Problems and research
needs. CRC Crit. Rev. Toxicol. 10:265-274.
21. 	Moser, V.C. (ed.) (1997) Neurobehavioral screening methods: A report of the International Programme
on Chemical Safety's collaborative study on neurobehavioral screening methods. NeuroToxicology 18
(#4:Special Issue):925-1083.
22. 	Moser, V.C., McCormick, J.P., Creason, J.P., and MacPhail, R.C. (1988) Comparison of chlordimeform
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and carbaryl using a functional observational battery. Fund. Appl. Toxicol. 11:189-206.
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needs and priorities for toxicity testing. Vol. 2. National Academy of Sciences Press. Washington, D.C.
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Neurotoxicology and Teratology 13:569-573.
26. 	O'Donoghue, J.L. (1989) Screening for neurotoxicity using a neurologically based examination and
neuropathology. J. Am. College Toxicol. 8:97-115.
27. 	Paule, M.G. (1990) Use of the NCTR operant test battery in nonhuman primates. Neurotoxicology and
Teratology 12(5):413-418.
28. 	Paule, M.G., Schulze, G.E. and Slikker, W. Jr. (1988) Complex brain function in monkeys as a baseline
for studying the effects of exogenous compounds. NeuroToxicology 9(3):463-470.
29. 	Rees, D.C., Francis, E.Z. and Kimmel, C.A. (1990) Qualitative and quantitative comparability of human
and animal developmental neurotoxicity. Neurotoxicology and Teratology 12(3):171-292.
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10:354-368.
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N.Y.
32. 	Rodier, P.M. (1990) Developmental neurotoxicology. Toxicologic Pathology 18:89-95
33. 	Schulze, G.E. and Boysen, B.G. (1991) A neurotoxicity screening battery for use in safety evaluation:
Effects of acrylamide and 3,3-iminodipropionitrile. Fund. Appl. Toxicol. 16:602-615.
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Press Inc.: San Diego.
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detection of neurotoxic disease. In, Experimental and clinical neurotoxicology. (P.S. Spencer and H.H.
Schaumberg, eds.) Williams and Wilkins Press. Baltimore, MD. pp.743-757.
37. 	Spencer, P.S. and Schaumburg, H.H., eds. (1980) Experimental and clinical neurotoxicology. Williams
and Wilkins Press. Baltimore, MD.
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Teratology 9:427-443.
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40. 	Tilson, H.A. and Moser, V.C. (1992) Comparison of screening approaches. Neurotoxicology 13:1-13.
41. 	Tupper, D.E. and Wallace, R.B. (1980) Utility of the neurological examination in rats. Acta
Neurobiol.Exp. 40:999-1003.
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Poisons of the Nervous System. U.S. Government Printing Office: Washington, D.C. OTA-BA-436.
43. 	U.S. Environmental Protection Agency (EPA) (1985) Toxic Substances Control Act Test Guidelines Final
Rule, 40 CFR Part 798, Health effects guidelines, Subpart G - Neurotoxicity. Fed. Reg. 50:39458-39470.
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requirements final rule. 40 CFR Parts 79 and 799. Fed. Register 53:5931-5953.
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Links on this page:
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Chapter V
Additional Recommended Studies
A. Introduction
The Age ncy recognizes that information about metabolism and pharmacokinetics, neurotoxicity, and
immunotoxicity are significant endpoints in assessing the safety of direct food additives and color additives used
in food. Recom mended strategies for improving the ability to determine m etabolism and pharm acokinetics and
the neurotoxic and imm unotoxic potentials of test substances are described in Chapters V B, C, and D,
respectively. Because this chapter addresses toxicity studies that are recommended for the first time by FD A for
assessing the safety of direct food additives and color additives used in food (see Figure 4, Chapter III C 1), they
are discussed in greater detail than other recomm ended toxicity studies (see Chapter IV C).
1. Metabolism and Pharmacokinetics
FD A be lieves tha t data from studies on the adso rption, distribution, m etabolism , and exc retion of a
chem ical can provide in sight into m echa nism s of toxicity an d are ess ential in the design a nd eva luation of res ults
from other toxic ity studies. Su ch data should b e provide d for all direct food additive s and c olor additive s used in
food that are assigned to Co ncern L evels II or III. Recomm endations for obtaining data on the metabolism and
pharmacokinetics of these substances are presented in this document. In general, the Agency recomm ends that
this information be obtained before subchronic and chronic toxicity tests are begun.
2. Neurotoxicity
It is recomm ended that the assessment of neurotoxic potential be carried out according to a process of
tiered testing progressing from the identification of chemicals associated w ith neurotoxic effects (screening),
through a chara cterization of the scop e of nervo us system involve me nt (characterization of effects), to the
determination of dose response kinetics which includes the definition of the no-observed adverse effect level
(dose-re sponse). Screenin g for neuro toxic effec ts, which is conside red to be o ne of the m ost critical step s in this
tiered process, should be routinely and systematically carried out in short-term (see Chapter IV C 3), subchronic
(see Chapter IV C 4), and reproductive and developmental toxicity (see Chapter IV C 9) studies. The
neuroto xicity scree n should include a spec ific histopath ologica l exam ination of rep resentativ e tissue sa mp les of all
major areas of the brain, spinal cord, and peripheral nervous system in conjunction with a functional evaluation
battery of quantifiable observations and manipulative tests selected to detect signs of neurological, behavioral, and
physiological dysfunctions. References to published literature that can guide the petitioner in selecting an
appropriate neurotoxicity screen are included.
Study reports shou ld include an integ rated ass essm ent of the p otential for the test chem ical to adv ersely
affect the structural or functional integrity of the nervous system. This assessment should include results of the
neurotoxicity screen and other toxicology data, as appropriate. Based on the assessment, an explicit statement
should be made as to whether or not the test chemical represents a potential neurotoxic hazard which requires
specia l testing. Re com me ndation s abou t further neuro toxicity testing , if the results of the initial scre ens indic ate
the nee d for such te sting, are inclu ded. H ow ever w e urge p etitioners to c onsult w ith Ce nter scien tists before
undertaking additional neurotoxicity tests.
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3. Immunotoxicity
An imm unotoxicity screen should be routinely carried out in short-term (see Chapter IV C 3), subchronic
(see Chapter IV C 4), and reproductive and developmental toxicity studies (see Chapter IV C 9). This screen
consists o f prim ary indica tors of immunotoxicity described in Chapter V D 3; these indicators are a set of
hematological, serum protein, histopathological, and body and organ weight endpoints that are routinely evaluated
in standard toxicity tests.
Study reports shou ld include an integ rated ass essm ent of the p otential for the test chem ical to adv ersely
affect the im mu ne syste m. T his assess me nt should be bas ed on re sults of the im mu notoxic ity screen (prima ry
indicato rs of imm unotox icity) and o ther toxico logy da ta, as appro priate. Ba sed on the results of this a ssessm ent,
an exp licit statem ent shou ld be m ade a s to wh ether or no t the test che mic al represe nts a pote ntial im mu notoxic
hazard which requires additional immunotoxicity testing (see Chapter V D 4 and 5).
If results of the immunotoxicity screen indicate the need for further testing, information that will help the
petitioner c hoose additiona l imm unotox icity tests is provid ed. Ho we ver, we urge pe titioners to con sult with
Cen ter scientists before undertaking additional imm unotoxicity tests.
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V B. Metabolism and Pharmacokinetic Studies
Results from anim al toxicity studies are used by FDA to determine dose-response characteristics for any
effects ob served in the eva luation of the safety of foo d and c olor additive s. Since the delivere d dose of a
substance to any affected tissue or organ is determined by the pharmacokinetics and metabolism of the substance
in the test animal, toxicity studies are more easily interpreted, likely to achieve target doses, and avoid excessive
to xic ity if d ata fro m me ta bo lic an d p ha rm a co kin etic stu die s a re av aila ble du rin g th e p la nn in g o f sh ort-te rm ,
subchronic and/or chronic toxicity studies. Early determination of metabolic pathways and the rates of
me tabolism in different test spe cies m ay prov ide exp lanation s for specie s difference s in any e ffects w hich are
observed, and suggest biochemical or pharmacologic experiments which might be used to test explanations of
suc h ph enom ena.
The Age ncy recomm ends that petitioners submit data that will enable our scientists to evaluate: 1) the
extent of absorption, 2) tissue distribution, 3) pathways and rates of metabolism, and 4) rate(s) of elimination of
the parent substance and any metabolites formed for all Concern Level II and III substances (see Figure 3). The
Ag ency ma y recom me nd subm ission of ad ditional m etabolic and ph arm acok inetic da ta base d on the extent to
wh ich a ch em ical is m etaboliz ed, the po tential toxic ity of the m etabolite s, and the e xtent to w hich ob served toxic
effects seem to correspon d to the presence of the parent substance or its metabolites.
1. Considerations in the Design of, Analysis of, and Use of Data from Metabolic and
Pharmacokinetic Studies
Pharmacokinetic data can be used to predict plasma concentrations, target tissue doses, and the fate of the
adm inistered do se. This info rma tion can then he lp the pe titioner and /or the A genc y: 1) decid e w hich tox icity
studies should be conducted, 2) select doses for chronic toxicity and carcinogenicity studies, 3) determine the
me chanism of toxicity and assist in the interpretation of toxicity data, and 4) improve the risk assessment process.
a. Design and Analysis of Metabolic and Pharmacokinetic Studies
Pharmacokinetic studies are most useful when they are performed early in the process of evaluating the
toxicity of a chemical. However, additional metabolism and pharmacokinetic studies may be recomm ended after
target organs have been identified in toxicity studies.
W hole animal (oral dosing) studies should be performed to determine gastrointestinal absorption and
overall e limina tion rates for a c om pound . How ever, it is often m ost efficient to p erform in vitro studies of
metabolism before whole animal (oral dosing) studies to determine whether enzyme kinetics may explain known
dose response curves or predict non-linear dose response curves. The results of early in vitro studies also can be
use d to optim ize the cho ice of do ses in w hole an im al pharm acokinetic studies.
Ad ditional rec om me ndation s conc erning the design a nd ana lysis of m etabolism and ph arm acok inetic
stud ies are des crib ed below .
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i. Test Com pound
In selecting the dosa ge form of a test com pound to be ad min istered in m etabolic and ph arm acok inetic
studies, the chemical characteristics of the compound and its route of administration should be considered. The
formulation of the test substance used for metabolic and pharmacokinetic studies should exhibit similar patterns of
disintegration and/or dissolution as formulations used for toxicity studies. Chem ical purity of the test compound
should be established; imp urities that may affect absorption, distribution, metabolism and excretion of the test
com pound should b e identified . Stability of the c om pound in its carrier (i.e., food, wate r, or solvent) also sh ould
be determined. Chemical characteristics of the compound (i.e., low solubility, volatility) may make certain routes
of administration impossible. It is critical that the dose absorbed into tissues be determined especially in studies
where the test substance is added to the feed or water and is ingested ad libitum.
Use of radioac tive substa nces fa cilitates m ass bala nce de term inations b ecau se radio-lab els are rela tively
easy to detect in samples of tissues and body fluids. Determining the disposition pattern of the radio-label may be
adeq uate for pre dicting do ses that sh ould be used in tox icity studies w here the results of a test a nim al's overall
exposure to the substance (parent compound and m etabolites) is of concern. The radio-label should not be
biologically labile; when a radioactive element is present at more than one position of the test compound, the
radio-label should be uniformly distributed in the molecule.
The radiochemical purity of the test substance (radioactivity actually associated with the compound being
tested) is another important consideration. If the test compound is not radiochemically pure and radio-labeled
impurities are not identified, and if only the distribution of the radio-label in tissues and body fluids is determined,
interpretation of the results may be difficult. For example, for a compound that is 95-96% radioactively pure and
minimally absorbed (i.e., approximately 2% absorbed), it is impossible to unequivocally differentiate between 2%
absorption of the test compound and 100% absorption of a radioactive impurity present at 2%.
ii. An ima ls
Metabolic and pharmacokinetic data from two rodent species (usually the rat and mouse) and a non-
rodent species (usually the dog) are recomm ended. If a dose dependency is observed in metabolic and
pharmacokinetic or toxicity studies with one species, the same range of doses should be used in metabolic and
pharmacokinetic studies with other species. If human metabolism and pharmacokinetic data also are available,
this inform ation sho uld be u sed to he lp select te st specie s for the full range of toxicity tests, an d m ay help to
justify using data from a pa rticu lar species as a hu m an surro gate in safe ty assessm ent and risk as sessm ent.
(Huma n metabolism studies should be conducted according to the guidelines in Cha pter V I B.)
Metabolism and pharm acokinetic studies have greater relevance when conducted in both sexes of young
adult animals of the same species and strain used for other toxicity tests with the test substance. The number of
animals used in metabolism and pharmacokinetic studies should be sufficient to reliably estimate population
variability (see Chapter V B 1 e). A single set of intravenous and oral dosing results from adult animals, when
combined with some in vitro kinetic results, may provide an adequate data set for the design and interpretation of
short-term, subchronic and chronic toxicity studies.
Studies in mu ltiple species may clarify wh at appear to be contradictory findings in toxicity studies (i.e.,
equa l mg /kg bw doses h aving le ss effect in on e spec ies than in anothe r). If disposition and m etabolite profiles are
found to be similar, then differences in responses among species could more reliably be attributed to factors other
than differences in metabolism. Studies of the pharmacokinetics and metabolism of a substance in neonatal and
adolescent animals provide information about any changes in metabolism associated with tissue differentiation
and development. Animals with fetuses of known gestational age should be used for determining the disposition
of the test substance in the fetus.
iii. Route of Adm inistration
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The m ost critical parameters required in assessing human exposure and target tissue dose are the
gastrointestinal absorption rate and internal elimination rates (renal and hepatic) for the test compound. Without
an intravenous (IV) dosing study, it is very difficult to determine wha t percentage of a chemical is absorbed,
beca use the m aterial exc reted in the feces is co mp osed o f unabso rbed do se plus biliary and no n-biliary (m ucosa l)
elimination.
An intravenous study can provide accurate rates of metabolism-- without interference from intestinal
flora--plus rates of renal and biliary elimination, if urine and bile are collected. This route also avoids the
variability in d elivered dose a ssociate d with oral abso rption and ensures that the m axim um am ount of rad iolabel is
excreted in the urine or bile for purposes of detection. Once IV data and parameters are available, they can be
used with plasma concentrations from limited oral studies to compute intestinal absorption via the ratio of Areas
Unde r the (plasma and or urine) C urves or via simulations of absorption with gastrointestinal absorption mod els.
In single-dose pharmacokinetic studies of oral absorption, the primary concerns are with the extent of
absorptio n and p eak pla sm a or target tissue conce ntrations of the test substan ce. If the test veh icle affects g astric
em ptying, it m ay be n ecessary to us e bo th fasted an d no n-fa sted an im als for pharm acokinetic studies.
iv. Dosage Regimen
Selection of the dosing regimen for metabolism and pharmacokinetic studies depends on the type of
inform ation that is n eede d. Me tabolic a nd pha rma cokine tic param eters are u sually de term ined follow ing a sing le
adm inistration of the test com pound . Com paring pa ram eters obta ined from studies in w hich a ra nge of sin gle
doses have been administered can be used to determine the doses at which saturation of absorption, distribution,
me tabolism or excretio n occu rs. Multiple dosing stu dies ca n be use d to dete rmin e the po tential of a c om pound to
induce or inhibit its absorption, distribution, metabolism or excretion. Identification and quantification of the
major metabolites following administration of single and multiple doses may indicate whether saturation or
induction of a particular biotransform ation pa thwa y can o ccur.
In vitro experim ents m ay be u seful in scree ning for do se dep ende ncies, and provide m ore acc urate
descriptio ns of the en zym e kinetic s or other proc esses un derlying d ose de pend encie s observe d in the w hole
anim al. In vitro studies usually indicate identical metabo lic pathways an d me tabolism rates com parable to those
obtaine d from who le anim al studies b ut require few er anim als to perform and ca n be co mp leted in less time with
few er re sou rces. 1-3
v. Sampling
Bloo d (RB Cs, plas ma , and serum ), urine, and fece s are the m ost com mo nly collec ted sam ples. In
addition, a few representative organ and tissue samples should be taken, such as liver, kidney, fat, and suspected
target orga ns. Sam pling tim es shou ld depe nd on the substan ce be ing tested and the route of ad min istration. In
general, an eq ual num ber of blood sa m ples should be taken in each ph ase of the co ncentration-versus -tim e cu rve.
Intravenous (IV) studies usually require much shorter, and more frequent, sampling than is required for oral
dosing. Time spacing of samples will depend on the rates of uptake and elimination. In a typical IV study, blood
and tissue sam ples are taken in a "po wers o f 2" series, i.e. samples at 2, 4, 8, 16, and 30 (32) minutes, 1, 2, 4, 8,
and 16 hours. Similar coverage could be obtained with only 7 time points by using a "powers of 3" series: 3, 9,
and 30 (27) m inutes, 1, 3, 9, and 24 (27) hours. Oral dosing studies usually extend to at least 72 hours, or 5 plasma
half-lives, ensuring the excretion of 95% of the absorbed dose. The sampling schedule for an oral dosing
expe rime nt m ight be: 15 min utes, 30 m inutes, 1, 2, 4, 8, 24, 48, and 7 2 hours. Su ch a sa mp ling sche me wou ld
provide data coverage for evaluation of absorption, elimination, enterohepatic recirculation and excretion
processes.
W hole Body Autoradiography (WBA ) has been used with increasing frequency as a means of identifying
tissues which concentrate test substances. This technique allows a small number of animals (5 - 10) to be used for
screening purposes with a minimal investment in manual labor. FDA encourages the use of W BA with IV dosing,
000227

as a means of screening and selecting tissues of greatest relevance for later oral dosing studies. Animals used for
W BA should be sacrificed during the elimination phase, between 1 and 5 plasma half-lives, since bioaccumulation
at steady-state is the primary consideration in selecting specific tissues.
The num ber of anim als used in m etabolism and ph arm acok inetic studie s should b e large e nough to
reliably estimate population variability. In the case of rats and mice, tissue and/or blood sample size is usually the
limiting factor: ana lysis of the sub stance ma y require 1 ml o r mo re blood, bu t it is difficult to obtain m ultiple
blood samples of this size from one animal. As a consequence, a larger number of animals is required (3 - 4 per
time point, 7 - 9 time points) when small rodents are used. Such an approach has the advantage of allowing
limited sam pling of critical tissues (e.g. liver, fat) at each tim e point, an o ption w hich is usu ally una vailable with
large animals. The use of humans and large animals generally permits collection of multiple (serial) blood
samples. For outcrossing populations like humans and large animals, individual differences in the rates of
biotransform ation are likely to be greater tha n those o f inbred rode nt popu lations; und er these c ircum stance s, more
samples/sex/group may be needed to reliably estimate variability.
Individ ual m etabolism cag es a re re com m ended for collec ting urine an d feces in o ral dosin g stu dies.
Excreta should be collected for at least 5 elimination half-lives of the test substance. When urine concentrations
will be used to determine elimination rates, sampling times should be less than one elimination half-life (taken
directly from the bladder in IV studies); otherwise, sam ples should be taken at equ al time intervals.
vi. In Vitro studies
In Vitro measurem ents employing enzymes, subcellular organelles, isolated cells and perfused organs
may be used to augme nt the dose response information available from less extensive metabolic and
pharmacokinetic studies. Because in vitro system s gene rally are less c om plex tha n wh ole anim als, elucida tion of a
test compound's metabolic pathways and the pathways' kinetic characteristics may be facilitated. Such systems
can be used to measure binding, adduct and conjugate formation, transport across cell mem branes, enzyme
activity, enzyme substrate specificity, and other singular objectives. Biochem ical measurements that can be made
using in vitro systems include: Intrinsic clearances of enzymes in an organ or tissue, kinetic constants for an
enzyme, binding constants, and the affinity of the test compound and its metabolites for the target
macromolecules. The activity of a hepatic drug-metabolizing enzyme in vivo ma y be ap proxim ated by kinetic
c on sta nts th at a re ca lc ula te d fro m in vitro studies; w hen a first-orde r approxim ation is use d, the ratio of V max to Km
is eq ual to th e intrins ic clearance of the drug. 4,5 In vitro measurem ents made using readily accessible tissues and
body fluids from animals and man m ay also be useful in elucidating mechanisms of toxicity.
vii. An alysis of D ata
D ata fro m all m e ta bo lism a nd ph arm a co kin etic stu die s sh ou ld be an aly ze d w ith th e sa m e
pharm acok inetic m odel an d results sho uld be e xpresse d in the sa me units. Con centration units are ac cepta ble if
the orga n or sam ple size is re ported, but p ercent o f dose/orga n is usually a m ore m eaning ful unit. In genera l, all
sam ples should be ana lyzed for m etabolites that cum ulative ly represen t m ore than 1% of the do se.
A variety of rate constants and other param eters can be obtained from IV and oral dosing data sets,
provided that good c ove rage of the distribu tion , elim ination , and abs orption (oral dose) p hases is av aila ble.
Typical parameters calculated to characterize the disposition of a test substance are: half-lives of elimination and
absorption; area under the concentration-versus-time curve (AUC) for blood; total bo dy, renal an d m etabolic
clearances (Cl); volume of distribution (Vd ); bioavailability (F); and mea n residence and ab sorption times (MAT,
MRT). Som e of these param eters, such a s half-lives an d elim ination rate s, are easily c om puted from one an other;
the half-life is m ore eas ily visua lize d than the rate con stant. 6,7
Co mp utation of o ral absorp tion (ka) and elimination (E) rates is often complicated by the "flip-flop" of the
absorp tion and elim ination pha ses wh en they differ b y less than a factor of 3. 8 Bec ause o f these an alysis
problems, computation of absorption and elimination rates should not be attempted on the basis of oral dosing
000228

results alone.
Bloo d-tissue up take rate s (kj1) can often be app roxim ated from data at e arly (t < 10 m inutes) tim e points
in IV studies, provided that the blood has been washed from the organ (e.g. liver) or the con tribution from blood to
the tissue residue is subtracted (fat). High accuracy is not usually required since these parameters can be
optim ized to fit the d ata w hen the y are use d in m ore com plex m odels. Tiss ue-bloo d recyc ling rates (k1j) and
residence tim es c an be c om puted from partition co effic ients if estim ates of u ptake rate s are ava ilab le.
Tissue /blood pa rtition coefficien ts (Rj1) sho uld be d eterm ined w hen ste ady-state has bee n ac hieved.
Estimates based on samples obtained during the elimination phase following a single dose of the test substance
ma y lead to undere stima tes of this ratio in bo th elim inating an d non-e limina ting tissues u nless its half-life is ve ry
long. C orre ctio n of these v alues fo r elim ination has bee n de scribed by sev eral authors. 9,10
It may be im portant to determine the deg ree of plasma p rotein and red blood cell binding of the test
substance; calculation of blood clearance rates using plasma or serum concentrations of the substance that have
not been adjusted for the degree of binding m ay under- or over-estimate the true rate of clearance of the test
substance from the blood. This is usually done through experim ents in vitro.
Two classical methods used in the analysis of pharmacokinetic data are the fitting of sums of exponential
functions (2- and 3-compartment m amm illary models) to plasma and/or tissue data, and less frequently, the fitting
of arbitrary po lynom ial function s to the da ta (non-co mp artm ental an alysis).8,11,12
Non-com partmental analysis is limited in that it is not descriptive or predictive; concentrations must be
interpolated from data. The appeal of non-compartmental analysis is that the shape of the blood concentration-
versus-time curve is not assumed to be represented by an exponential function and, therefore, estimates of
me tabolic a nd pha rma cokine tic param eters are n ot biased by this assu mp tion. In order to m inim ize errors in
parameter estimates that are introduced by interpolation, a large number of data points that adequately define the
concentration-versus-time curve are needed.
Analysis of data using simple m amm illary, compartmental models allows the estimation of all of the
basic parameters mentioned above, if data for individual tissues are analyzed with 1 or 2 compartment models, and
combined with results from 2 - 3 compartment analyses of blood data. "Curve Stripping" analysis can be applied
to such simple m odels through the use of com mon spreadsheet program s (i.e. LOTU S 1-2-3), as long as a linear
regression function is provided in the program. Optimization of the coefficients and exponents estimated may
require the use of more sophisticated software: a number of scientific data analysis packages such as RS/1 and
SigmaPlot have the necessary capabilities. Specialized programs such as NONLIN 13, C O NS AM ,14 or
SIMUSOLV 15 will be needed when more com plex models must be analyzed. Coefficients and exponents from
mam millary models can be used to calculate other parameters; however, they should not be taken too literally,
since mam millary models assume that all inputs are to a central pool (blood), which communicates without
limitation into other compa rtments.16,17 This approach d oes not include details such as blood flow limitations,
anatom ical volum es o r other phys iolo gical lim its in the anim al.
Physiologically based pharmacokinetic models (PB-PK ) were developed to overcome the limitations of
simple mamm illary models. Physiologically based models describe the disposition of test substances via
com partm ental m odels w hich inc orporate a natom ical, bioche mic al and p hysiolog ical feature s of specific tissu es in
the w hole an ima l. The typ es of inform ation ad ded inc lude orga n-spec ific blood flow s, volum es, grow th m odels
a nd m eta bo lism ra te s. M e ta bo lic pa ra m ete rs o fte n a re ob ta in ed fro m in vitro studies (i.e., enzym e reactio n rates in
culture d he patocytes, pla sm a protein binding, etc.), while oth er param eters are b ecom ing ava ilable as sta ndard
param eters in the litera ture. Param eters from ma mm illary m odels ca n be use d to com pute the value o f param eters
used in physiological pharmacokinetic models, using tissue-specific blood flows, anatomical volumes, and other
inform ation (literature v alues). Estim ation of pa ram eters for a sim ple m am milla ry m odel is often the first data
reductio n step in c reating a physiolo gical m odel.5,18
Be cause PB -PK mo dels are b ased o n physio logical a nd ana tom ical m easure me nts and a ll ma mm als are
inherently similar, they provide a rational basis for relating data obtained from animals to humans. Estimates of
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predicte d disposition patterns for test su bstanc es in hum ans m ay be o btained by adju sting bioc hem ical para me ters
in models validated for animals; adjustments are based on experimental results of animal and hum an in vitro tests
and by substituting appropriate human tissue sizes and blood flows. Development of these models requires special
software capable of simultaneously solving multiple (often very complex) differential equations, some of which
were m entioned above. Several detailed descriptions of data analysis have been reported.7,19
b. Use of Data from M etabolism and Pharmacokinetic Studies
Inform ation from me tabolism and ph arm acok inetic studie s can b e used in the des ign and analysis o f data
from other toxicity studies. Some examples are described below.
Design of Toxicity Studies: The concentration-versus-time curve, peak, and steady-state concentrations
of the test substance in blood or plasma provide information on the distribution and persistence of the
substance in the animal which m ay suggest essential elements in the design of toxicity studies. For
example, when m etabolic and pharmacokinetic studies indicate that the test compound accum ulates in the
bone marrow, long-term toxicity tests should include evaluation of the test compound's effect on
hematopoietic function and morphology. If a test compound is found to accumulate in milk, an
investigator should plan to perform reproductive toxicity studies with in utero exposure and a nursing
phase (cross-fostering study; see Chapter IV C 8). In addition, information from m etabolic and
pharmacokinetic studies can be used to predict the amount of test compound that enters biological
com partm ents (tissue s, org ans, etc.) that may not suffer a toxic insult but may serve as depots for indirect
or secondary exposure.
Setting D ose L evels: There is conside rable de bate ab out the us e of m etabolic and ph arm acok inetic da ta
in se tting doses to be u sed in toxicity studies, particu larly chronic toxicity a nd c arcinogenicity studies.
Current NTP policy for selecting the highest dose in carcinogenicity bioassays is described in Chapter
IV C 6 b. In 1984, the NTP A d Hoc Panel on C hem ical Carcinoge nesis Testing and E valuation also
recom me nded that pha rma cokine tic data be conside red alon g with subch ronic toxic ity data in se tting all
dose levels except the m aximu m-tolerated dose (M TD ) in the carcinogenesis bioassay of chem icals.20
FDA agrees with these statements and recommends that pharmacokinetic data be used in conjunction
with the results of short-term and sub chronic toxicity stud ies to set ap propriate d ose leve ls for chronic
toxicity, reprod uction a nd teratolo gy studie s, and for setting d ose leve ls below the M TD (highest do se) in
carcin oge nicity studies.
De term ining M echa nism s of Tox icity: Information from metabolic and pharmacokinetic studies can be
used to supplement conventional toxicology data in elucidating mechanisms of toxicity. Metabolites
identified b y a pha rma cokine tic study c an sug gest m echa nism s unde rlying a tox ic respon se. Biolo gically
reactive interm ediates are often im plicated in a toxic res ponse ; how ever, such me tabolites a re usually
short-lived, reacting in the vicinity of their formation. The presence of potentially reactive intermediates
can be deduced indirectly by measuring the formation of characteristic macromolecular (DNA, RNA,
protein) adducts and metabolic conjugates. Measurement of metabolic conjugate vs adduct formation and
the affinity of a compound and/or its metabolites for the target molecule may help identify mechanism s of
toxicity and effe ctiv e routes of d etoxific atio n.
In fo rm a tio n fro m in vitro test systems concerning the formation of critically reactive metabolites may be
used to establish the relationship between the formation of the reactive metabolite in vivo and du ration of ex posure
to the test co mp ound. T his relationsh ip is imp ortant in circu ms tance s where critically re active m etabolite s are
only form ed wh en the cap acities of no rm al m etabolic and o ther defensive or adaptiv e m echanism s are exc eeded.
Determining the concentrations of the test substance at which saturation of binding occurs may indicate at what
conc entration a com pound is likely to dep lete deto xifying co njugation pools an d beco me availab le to react w ith
target macrom olecules.
Improving the R isk Assessm ent Process: Information from metabolic and pharmacokinetic studies
increasingly is being incorporated into risk assessments. Conventional risk assessments typically involve
000230

linear extrapolation of external dose and an inter-species scale factor based on body weight or body
surface area. Risks calculated by this approach may be under- or over-estimated. Many of the biological
processes involved in the absorption, distribution, metab olism and e xcretion of a com pound are dose
depende nt and, th erefore , the toxicity observed may not be a sim ple functio n of adm inistere d do se.
Developm ent of appropriate pharmacokinetic models may enha nce our ability to use metabolic and
pha rm acokinetic in form atio n in risk assessm ent.
2. Recommended Metabolism and Pharmacokinetic Studies
FD A be lieves tha t data from studies on the abso rption, distribution, m etabolism , and exc retion of a
chemical can provide insight into mechanism s of toxicity of chemicals and are essential in the design and
evaluation of results from other toxicity studies. FDA believe s that a set of basic pharmac okinetic and m etabolism
studies sh ould be perform ed for all Co ncern L evel II and III substances, but that additional studies may be
recommended for a particular additive. Recommended studies should be performed with two rodent species
(usually the rat and mouse) and one non-rodent species (usually the dog). In general, what constitutes an
approp riate set of m etabolism and ph arm acok inetic studie s will de pend on the a nticipate d degre e and ty pe of toxic
response to a test compound and by the estimated m agnitude of human exposure to the compound. The
recommended set of basic studies are:
4 Intravenous studies using a tracer level dose should be conducted in adult male and female animals of
specie s in wh ich toxicity studies ha ve alrea dy bee n cond ucted o r in whic h chron ic toxicity stud ies are
contemplated. Blood, liver, and fat samples should be taken at all time points. The size and timing of
urin e an d bile sa m ples w ill de pend o n the do se o f trac er and rate of excretio n by eac h of these ro utes.
Samples taken over periods of 30 min to 2 hours, at 2 or 3 time points, should be sufficient for
computation of the cumulative excretion by these routes. Plasma, urine and bile should be analyzed for
metabolites of the test substance that cumulatively represent more than 1% of the dose. Estimates of
uptake and elim ination rates should be ma de for each tissue sam pled, using 2-compa rtment m odels.
4 Studies of the rate of metabolism (of the parent compound) as a function of dose (or concentration)
should be conducted in vivo or in vitro, guided by results of metabolite analyses from the intravenous
studies and available toxicology information. Hepatocytes or perfused livers will normally be used for
such studies, but an examination of the distribution of metabolites between the plasma, bile and urine
a fte r IV do sin g m a y in dic ate th at th e k id ne y is im p orta nt in th e m e ta bo lism o f so m e c he m ic als. E nz ym e
k in etic pa ra m ete rs re su ltin g fro m in vitro studies m ay be s caled up to w hole orga n rates an d used to
predict rates of metabolism in the whole animal as a function of dose.
4 Oral dosing studies should be conducted in ad libitum fed animals, to determine the rate and
cumulative absorption of the substance. Dosage and sampling times should be selected on the basis of
results from toxicity tests, metabolic dose response data (ii, above), and elimination rates determined
from IV dosing stud ies. Bioaccum ulative tissu es shou ld be sa m pled in add ition to blood , urine an d feces.
A tissue that doe s not acc um ulate the substan ce sho uld also b e includ ed for referen ce purp oses. W hole
Body Autoradiographic studies are recomm ended as a method for identifying bioaccumulative tissues
prior to the initiation of oral dosing studies.
3. Additional Studies
Studies of enzyme induction and potential pharmacological adaptation should be conducted whenever
chronic studies are recomm ended. The resulting information can be incorporated into multiple or continuous
dosing m odels to sim ulate the plasm a and tissu e levels o f test substan ce ex pecte d for a variety of doses in chronic
studies being planned.
In cases where reproductive studies are recomm ended, pharmacokinetic experiments evaluating the
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distribution of the substance in the fetus, mother's milk, and neonates should be performed as an aid in selecting
doses and designing reproductive toxicity studies. If the metabolic potential of the fetal and/or neonatal liver can
be assessed in a preliminary in vitro study, this step is highly recommended.
Assu min g that IV and ora l dosing stud ies have already been c om pleted for b oth m ale and fem ale adu lt
animals prior to the reproductive pharmacokinetic studies, sampling can be more limited, ie. excretion studies
combined w ith limited sampling of maternal blood, fetuses, milk, and neonatal tissues may be sufficient for
characterization of the metabolic and pharmacokinetic processes of interest in pregnancy.
Depending on the types of toxic effects observed and the importance of understanding the mechanisms of
these e ffects to the sa fety assessm ent of a dire ct food or c olor additive used in foo d, additiona l bioche mic al or in
vitro experim ents m ay be s ubm itted by the petitioner in su pport of an y m echa nism propose d. Such studies sho uld
be substance-sp ecific, a nd shou ld be ba sed on c ons ulta tion with C FS AN, as appropriate .
Chapter V B: Metabolism and Pharmacokinetic Studies
1. Bä ärnhielm , C., Dah lbäck, H . and Sk ånbe rg, I. (1986) In vivo pharmacokinetics of felopidine predicted
fro m in vitro stud ies in rat, dog , and man. Acta Pharmacol.Toxicol. 59:113-122.
2. Green, C.E., LeValley, S.E. and Tyson, C.A. (1986) Comparison of amphetam ine metabolism using
isolated he patocytes from five spe cies inc luding hum an. J.Pharmacol.Exp.Ther. 237(3):931-936.
3. Lin, J.H ., Sugiyam a, Y., Aw azu, S. an d Ha nano , M. (198 2) In vitro and in vivo evaluation of the tissue-to-
blood p artition coe fficient for p hys iolo gical pharm acokinetic m ode ls. J.Pharmacokin.Biopharm. 10:637-
647.
4. Rane, A., Wilkinson, G.R. and Shand, D.G. (1977) Prediction of hepatic extraction ratio from in vitro
m easure m ent of in trins ic clearance. J.Pharmacol.Exp.Ther. 200:420-424.
5. Gillette, J.R. (1986) On the role of pharmacokinetics in integrating results from in vivo and in vitro
stud ies. Fd.Chem.Toxicol. 24:711-720.
6. W agne r, J.G. and N elson, E . (1963) Pe rcent ab sorbed tim e plots de rived from blood lev el and/o r urinary
excretion data. J.Pharm.Sci. 52:610-611.
7. Gibaldi, M ., and Perrier, D., e ds. (1 982 ) In, Pharmacokinetics. 2nd edition. Marcel Dekker Publishing Co.
New York, N.Y.
8. Notari, R .E. (1 987 ) In, Biopharmaceutics and Clinical Pharmacokinetics. Marcel Dekker Publishers, Inc.
New Yo rk, N .Y. Cha pter 4.
9. Ch en, H.S . and G ross, J.F. (1979) E stima tion of tissue-to-p lasm a partition c oefficients u sed in
phy siological pharm acokinetic m ode ls. J.Pharmacokin.Biopharm. 7(1):117-125.
10. Lam , G., Che n, M -L. and C hiou, W .L. (1982) D eterm ination of tissue -to-blood pa rtition coefficien ts in
phy siologically-b ase d ph arm acokinetic studies. J.Pharm.Sci. 71:454-456.
11. Benet, L.Z. (1972) General treatment of linear mamm illary models with elimination from any
com partm ent as u sed in ph arm acokinetics. J.Pharm.Sci. 61:536-541.
12. Va ugha n, D.P. and Traino r, A. (1975) D erivation o f genera l equation s for linear m am milla ry m odels
when the drug is ad m inistere d by diffe rent routes. J.Pharmacokin.Biopharm. 3:203-218.
000232

13. Pedersen, P.V. (1977) Curve fitting and modeling in pharmacokinetics and some practical experiences
with N ONLIN and a ne w program FU NFIT . J.Pharmacokin.Biopharm. 5:513-531.
14. Bo ston, R.C ., Palme r, M.S., Go lden, P.D . and R am berg, C .F. (1988) U sers notes for enhan cem ent to
SAAM /CONSA M V ersion 30 resource facilities for kinetic annalist. Contact the authors at the National
Institute of Health, Building 10, Bethesda, Maryland.
15. Steiner, E.C., Rey, T.D., McCroskey, P.S. (1990) Simusolv modeling and simulation software reference.
Dow Chem ical Co. Midland, Michigan.
16. Resc igno, A . and Segre, G. (1 966 ) In, Drug and Tracer Kinetics. 1st Am erican e dition. Bla isdale
Publishing C o. W alth am , M A. p. 91.
17. Faga rasan, J.T. an d DiS tefano, J.J. (1989) H idden o scillations in g eneraliz ed linea r ma mm illary
com partm ental m ode ls. Math.Biosci. 93:79-95.
18. O'Flaherty, E .J. (1989) Interspe cies co nve rsion of kinetic ally equ ivalent doses. Risk Anal. 9:587-598.
19. Gerlowski, L.E. and Jain, R.K. (1983) Physiologically based pharmacokinetic modeling: principals and
applic atio ns. J.Pharmacol.Sci. 72(10):1103-1127.
20. National Toxicology Program Ad Hoc Panel (1984) In, report of the National Toxicology Program Ad
Hoc Panel on Chem ical Carcinogenesis te sting an d ev aluatio n. pp.125-127.
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V D. Immunotoxicity Studies
Exposure to various che mica ls has been associated w ith toxicity of the imm une system in animals; these
include environmental contaminants, chemicals in the occupational environment, and direct and indirect food
additiv es. R egulatory age ncies, including FD A, 1 have recognized the importance of these types of effects for
assessin g the safe ty of chem icals to w hich hu ma ns m ay be e xpose d. Bec ause o f the rapid e me rgence of the field
of imm unotox icology during the past tw o deca des an d the ab unda nce of info rma tion that ha s accu mu lated w ith
regard to th e im mu ne syste m a s a target org an, various federal ag encie s and inte rnationa l organiza tions are
preparing guideline s for the con duc t of im m uno toxicity stud ies. 2-6 In addition, various testing approaches have
been propos ed by re sea rchers in the fie ld. 7-13
1. Immunity: A Brief Review
Th e im m une system has bee n de scribed in detail in a nu m ber of excelle nt reviews. 14-18 Thus, only those
asp ects of im m unity w hich are pa rticu larly rele vant to im m uno toxicity testing will be review ed in this se ctio n.
Imm unolog ical func tion enc om passes a com plex array of participatin g cell type s and org an syste ms . Imm unity
ma y be defined in relation to the function of the various cellular compone nts.
a. Hum oral Immunity
Hum oral imm unity is defined in terms of the B-lymphocytes (B-cells), the antibody producing cells of the
immune system. The B-cells, named because of their functional similarity to antibody-producing cells derived
from the B ursa of Fa bricius in birds, are found prim arily in the sple en, lym ph nod es, Peye r's patches in the gut,
peripheral blood and bone marrow. The bone marrow is also the site of origination of B-cell precursors, the stem
progenitor cells.
Imm unoglo bulins (Igs), the cla ss of proteins th at is com prised of the antibod ies, are further cla ssified w ith
regard to particular peptide regions found on the light and heavy chains. At least five major classes of
imm unoglo bulins ha ve bee n define d for m an and anim als: IgA , IgD, IgE, IgG , and IgM . Antibod ies function in
concert with com pleme nt proteins that are produced in the liver and by m acrophages to provide protection ag ainst
bacterial and viral infections. Antibodies also help protect man and animals from agents that cause tumors and
from som e sp ontaneously occ urrin g tum or cells.
Humoral immunity can be further classified with regard to the dependence of antibody production on T-
lymph ocyte help: T-cell depen dent and T -cell independent im mun ities.
b. Cell-M ediated Immun ity (CM I)
CM I derives its name from classical studies that demonstrated adaptive cell transfer of imm unological
functio n, gra ft v. host reactiv ity, etc. C M I is associated with the T -lym pho cytes or T -cells (th ym us-d eriv ed).
Various classes of T-cells have been described, such as suppressors, helpers, inducers, and cytotoxic cells. Some
of these T -cell types a re involve d in B -cell im mu noregu lation. T-ce lls secrete v arious pe ptide fac tors, referred to
as lymphokines or cytokines, that modulate the activity of B- and T-cells. Cytotoxic T-cells participate in direct
killing of invading microorganisms and tumor cells. T-cells are now com monly defined in terms of various
me mb rane "a ntigens" , such as T -4 (or CD 4) for helper/c ytotoxic c ells and T -8 (or CD 8) for suppres sor/cytotox ic
cells.
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c. Non-S pecific Immunity
Non-specific immunity is derived from other cell types that participate in the imm une process. Natural
killer (NK) cells are a group of cells that share certain properties with T-cells, but probably arise from different
stem progenito r cells. 19 These ce lls are known to play an im portant role in imm une surveillance against
sponta neou s tum or form ation. Th ey also s erve as a first line of defen se, in coop eration w ith other ph agoc ytic
leukocytes (phagocytes or granulocytes), in the destruction of invading viruses and bacteria. Macrophages
(activated monocytes) play a key role in antigen processing and presentation to lymphocytes; they interact with the
T- and B-cells to facilitate antibody production. These cells also secrete cytokines, such as interleukin-1, which
mod ulate certain T-cell functions.
M odulation of host resistan ce to infec tious organ isms can be the result of eith er direct or ind irect effects
on various cell components. Reduction in host resistance is referred to as imm unosuppression. Severe or
prolonged imm unosuppression, as manifested in acquired imm unodeficiency syndrome (AIDS), can result in an
overwhelming num ber of infections, tumor formation, and death. Imm une enhancement or hyperactivity of the
imm une system can result in hypersensitivities, such as allergic disorders and autoimm une diseases. The
me chan isms of these diso rders and disease s are com plex an d are de pend ent on fac tors such a s gene tic
predisposition, age, medical condition, and environment. The development of autoimm unity, which has been
associate d w ith th e us e of various dru gs, 20 can have a pronounced toxic effect on a nu mbe r of organ systems.
True allergic reactions, which are mediated mainly by IgE in man and certain animals, can result in a life-
threatening condition known as anaphylactic shock. Certain food additives, such as sulfites, have been restricted
in use b ecause o f their hig h se nsitizin g po tential. 21 Othe r food che mic als have been a ssociate d with
hypersensitivity-like conditions such as the toxic oil syndrome 22 and tryptophan-induced eosinophilia myalgia.23
2. Key Concepts in Immunotoxicity Testing
These guidelines relate to the safety assessment of direct food additives and color additives used in food;
such assessments are done on a case-by-case basis. The recomme ndations for immunotoxicity testing of food and
color additives used in food presented in this section may or may not be relevant to those of other agencies and
organizations. However, certain concepts from which these recomm endations derive are shared by various
others10,11,12,24 including the W orld He alth Organizatio n. 6 Other conce pts may b e unique to FD A, since these
guidelines have been developed within the toxicity testing framework set forth in this book. These concepts are:
4 Tw o types o f imm unotox icity tests/proc edures are define d: Typ e 1 T ests are those that do no t require
any pe rturbation of the test anim al, such as im mu nization and ch allenge with a n infectiou s agen t.
i) P rim a ry in dic ato rs o f im m un e to xic ity are de riv ed fro m Ba sic Ty pe 1 T ests, such as
hematology and serum chem istry profiles, routine histopathology examinations, and organ and
body w eight m easure me nts from standard toxicity stud ies desc ribed in oth er section s of this
book. Additional procedures, such as measurements of thymus w eights and performance of
more definitive histopathological evaluations of imm une-associated organs and tissues, have
been add ed.
ii) In dic ato rs o f im m un e to xic ity ca n a lso co m e fro m Exp ande d Ty pe 1 T ests. These tests are
logical extensions of Basic Type 1 tests; for example, Expanded Type 1 tests may extend the
hematology, serum chemistry, and histopathology evaluations of standard toxicity studies. Many
of these expanded tests can be performed with the same blood and tissue samples collected for
the Basic Type 1 tests; in addition, many of the expanded tests can be performed retrospectively.
4 Typ e 2 T ests include injection s or e xpo sure to test an tige ns, vaccines, in fectiou s ag ents or tum or cells.
If Type 2 tests are to be performed concurrently with a standard toxicity study, a satellite group of
animals should be added to the recomm ended number of test animals in the study. Protocol designs for
standard toxicity studies that include a satellite group of animals for Type 2 immunotoxicity tests will be
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recom me nded whe n availa ble inform ation indic ates that a test com pound ma y presen t an im mu notoxic
risk.
4 Sets of Basic and Expand ed Type 1 Tests are defined as Lev el I Imm unotox icity Te sts. Som e Le vel I
tests scree n for im mu notoxic effects in test a nim als; others foc us on de fining an im mu notoxic effect m ore
specifica lly, such as d eterm ining the m echa nism or cell type s involve d. Ana logously , sets of Typ e 2 tests
are defined as Lev el II Imm unotox icity Te sts; Lev el II tests also ca n be use d to scree n for, or mo re
specifically define, immunotoxic effects of food and color additives used in food.
3. Indicators of Possible Immune Toxicity
Ba sic Ty pe 1 T ests: Prim ary Indica tors
The primary indicators of possible immune toxicity are derived from routine measurements and
exam ination s pe rform ed in toxicity studies recom m ended in other se ctio ns of this pub lica tion (Basic T ype 1 tests).
Indicato rs derived from sh ort-term and sub chronic toxicity stud ies, and de velopm ental toxic ity studies w ith
rodents are listed below. If a substance produces one or more of these primary indicators of immune toxicity,
more definitive imm unotoxicity tests (Expanded Type 1 tests or Type 2 tests) may be recomm ended; such
decisions will be m ade on a ca se-by-case basis.
a. Indicators from Short-Term and Subchronic Toxicity Studies
4 He ma tology Ind icators: Elevation or depression in white blood cell (WBC ) counts; altered differential
W BC counts; lymphocytosis and lymphopenia; and eosinophilia.
4 Clinic al Ch em istry Indicators : Elevated or reduced total serum protein in combination with an
abno rma l album in-to-globulin (A/G ) ratio. Other ind icators often associa ted w ith imm unolog ic
dysfunction include abnormal levels of liver proteins and enzymes, such as albumin and the
transaminase s.
4 Histop atholog y Indica tors: Abnormalities found during gross and routine histological evaluation of
the lym pho id tissue s, e.g. spleen, lym ph nod es, thym us, gut-assoc iated lym phoid tissu e (GA LT , in
particular Peyer's patches), and bone marrow. Morphologic abnormalities such as scattered, focal mono-
nuclear cell infiltrates in non-lymph oid organs (e.g. kidney and liver) may be relevant to autoimmune
disease. If differences are seen in any lymphoid tissue, attention should be given to "cellularity" and
prevalence of activated macrophages. The description could include in situ descriptions of the types of
cells, density of the cell populations, lymphocyte distribution relative to distinguishing structures or
define d areas of th e organ. (In these instances, the effect does not need to be defined rigorously for
each animal. The number of animals observed, however, should be a statistically significant
sam ple size.) The histopathological analysis of routinely stained (hematoxylin and eosin) samples of the
spleen should inc lude de scriptions of lym phoc yte distribution and pro liferation in kn ow n T- an d B -cell
areas, such as the germinal centers (for B-cells) and the periarteriolar lymphocyte sheath (PALS) for T-
cells if abnormalities are observed. The histopathologic analysis of the lymph nodes and Peyer's patches
should include a description of the imm une activation (i.e. the relative number of follicles and germinal
centers) when abnormalities or lesions are observed in these organs. W hen abnormalities of the thymus
are obse rved, histopa thologic a nalysis sh ould be descriptive and qu antitative a s possible with reg ard to
atrophy and ne crosis and other obs ervation s. If the test com pound is show n to either stim ulate ce ll
proliferation, or to cause atrophy and cell depletion in any lymphoid organ, the effect is likely to be
viewed as a potentially immunotoxic effect requiring more definitive testing.
4 Orga n and B ody W eight Indic ators: Elevated or depressed spleen and thymus weights; elevated or
depressed organ-to-body-weight ratios for the spleen and thymus (statistical treatment of the organ-to-
bod y-w eight ratios should include an ana lysis of c o-varia nce, w ith body we ight as the co-varian t).
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Elevated or dep ressed body w eights, although primarily an indicator of endocrine function, may a lso
indicate indirect imm unotoxic effects, since endocrine function can significantly effect the immune
sy ste m .
b. Indicators from Developmental Toxicity Studies
4 M orbidity an d M ortality Indica tors: Unusual incidenc e of maternal infections.
4 Histop atholog y Indica tors: Abnormalities found during gross evaluation of the fetal liver, spleen, and
thymu s.
4 For animals in the F1 and F2 generations:
i) He ma tology Ind icators: Elevation or depression in white blood cell (WBC ) counts; altered
differential WBC counts; lymphopenia and lymphocytosis; and eosinophilia.
ii) Clinic al Ch em istry Indicators: Eleva ted or redu ced tota l serum protein in co mb ination w ith
an abnormal albumin-to-globulin (A/G) ratio.
iii) Histop atholog y Indica tors: Abnormalities found during gross and routine histological
evaluatio n of the lym pho id tissue s, e.g. spleen, lym ph nod es, thym us, gut-assoc iated lym phoid
tissue (GAL T, in particular Peyer's patches), and bone marrow. Morphologic abnormalities such
as scattered, focal mono-nuc lear cell infiltrates in non-lymphoid organs (e.g. kidney and live r)
may be relevant to autoimm une disease. If differences are seen in any lymphoid tissue, attention
should b e given to "cellula rity" and p revalen ce of ac tivated m acroph ages. T he des cription co uld
include in situ description s of the type s of cells, dens ity of the ce ll populatio ns, lym phoc yte
distribu tion rela tive to distinguishin g structure s or d efin ed areas o f the organ. (In these
instances, the effect does not need to be defined rigorously for each animal. The number
of animals observed, however, should be a statistically significant sample size.) The
histopathological analysis of routinely stained (hematoxylin and eosin) samples of the spleen
should in clude d escription s of lym phoc yte distribution and pro liferation in kn ow n T- an d B -cell
areas, such as the germinal centers (for B-cells) and the periarteriolar lymphocyte sheath (PALS)
for T-cells if abnormalities are observed. The histopathologic analysis of the lymph nodes and
Peyer's patches should include a description of the immune activation (i.e. the relative number of
follicles an d ge rm inal centers) w hen ab norm alities o r lesions are observed in these organs.
W hen abnormalities of the thymus are observed, histopathologic analysis should be descriptive
and quantitative as possible with regard to atrophy and necrosis and other observations. If the
test com pound is show n to either stim ulate ce ll proliferation, or to ca use atrop hy and cell
depletio n in any lym phoid o rgan, the effe ct is likely to be view ed as a potentially imm unotox ic
effect requiring more definitive testing.
iv) Orga n and B ody W eight Indic ators: Elevated or depressed spleen and thym us weights;
elevated or depressed organ-to-body-weight ratios for the spleen and thymus (statistical
treatm ent of the o rgan-to-bo dy-w eight ratios sh ould inc lude an analysis o f co-varian ce, w ith
body weight as the co-variant). Elevated or depressed body weights, although primarily an
indicator of endocrine function, may also indicate indirect imm unotoxic effects, since endocrine
fu nc tio n c an sig nific an tly effe ct th e im m un e sy ste m .
4. Expanded Type 1 Immunotoxicity Tests
Assessing the safety of food and color additives used in food usually requires the completion of various
000237

toxicity studies. In addition to the screen of primary indicators of possible imm une toxicity provided by these
toxicity stud ies and s um ma rized ab ove, add itional tests for further e valuatio n of the im mu notoxic potential o f a
test substance m ay be recom me nded by the A gency. The a dditional tests can be Expan ded Typ e 1 Tests,
discussed in this section, or Type 2 Tests, discussed in the next section. The Agency's recomm endation that
specific imm unotoxicity tests be performed on test substances will be made on a case-by-case basis. Expanded
Type 1 immunotoxicity tests include:
4 He ma tology T ests: Flow cytom etric ana lysis of B -lym phoc ytes, T-lym phoc ytes, and T -lym phoc yte
subsets (TH + TS or CD4 and CD8); immunostaining (immunoperoxidase or immunofluorescence) of B-
lymphocytes, T-lymphocytes and T-lymphocyte subsets from peripheral blood or single cell suspensions
from the sple en. 25-29
i) He ma tology Ind icators: Decreased or elevated percentages of any of the various lymphocytes
relative to controls and abnorma lities in the B-ce ll/T-cell and the TH /TS (C D4/C D8) cell ratios;
these should be determined from differential counts of the imm unostained preparations or from
cytom etric ana lysis.
4 Serum Ch em istry Tests : Electrophoretic analysis of serum proteins to permit separation and
quantification of the relative percentages of albumin and the "-, $-, and J-globulin fractions;
quan tification of J-globulin fractions (IgG, IgM, IgA, and IgE); analysis of total serum complem ent and
components of complem ent (such as C3) from CH -50 determinations; immunochem ical assay of serum
cytokines, such as IL-2, IL-1, and J-interferon; qu antification of serum auto-an tibodies, suc h as an ti-
nuclear, anti-mitochondrial, and anti-parietal cell antibodies.
i) Serum Ch em istry Indicators: Statistically significant variations between experimental and
control groups of animals for any of the parameters listed above.
4 Histop atholog y Te sts: Immunostaining of B-lymphocytes in the spleen and lymph nodes, using
polyclo nal antibo dies to IgG of the test an ima ls; 30,31 immunostaining of T-lymphocytes and T-
lymph ocyte subsets in the spleen, using mo noclonal or polyclonal antibodies to various cell m arkers;
micro-metric measurements of germinal centers and PALS of the spleen and the follicles and germinal
centers of lymph nodes; morphome tric analysis of the relative areas of the cortex and medulla of the
thymu s, using routinely stained histopathology sections.
i) Histop atholog y Indica tors: Statistically significant variations between experimental and
control groups of animals for any of the parameters listed above, using both analysis of variance
(AN OV A) and a m ultiple comparison T -test, such as D unnett's.32
4 Tes ts for In Vitro Analysis of the Functional Capacity of Specific Cell Types:
i) Ac tivity of Na tural Kille r (NK ) Cells: The functional capacity of NK cells can be measured
using the classica l 51Cr ch rom ium release a ssay; 19 this assay is well standardized and has been
use d successfully with both mice and rats in va riou s im m uno toxicity stud ies. 33-35 Of particular
concern is reduced NK cell activity, which may be correlated with increased tumorigenesis and
infectivity.
ii) Mitogenic Stimulation Assays for B- and T-Lymphocytes: Certa in plant lec tins stimu late
blastogenesis and DNA synthesis of T- and B-lymphocytes: concanavalin-A (Con-A) and
phytohemagglutinin (PHA) are known to preferentially stimulate T-lymphocytes, and an extract
from pokew eed (P W M ) as we ll as certain b acterial lipo polysaccha rides (LP S) and protein
extracts are known to preferentially stimulate B -lymphoc ytes in vitro. Since the se assa ys are
carried ou t ex vivo, they can be perform ed on p reparation s of periphe ral blood. T he assa ys are
well characterized for use in various animals species (including man36), can be performed on
either peripheral blood or spleen-cell suspensions, and have been used in a number of
im m uno toxicity stud ies. 2,8,9,10,12,13,35,37 Both reduce d and e levated levels of bla stogen esis or 3H
000238

incorporation into DN A are of interest in the evaluation of the immunotoxic potential of food
and color additives used in food.
iii) Phagocytotic Index of the Macrophage: Variou s assays to determ ine the p hago cytotic
ability of m acrophages ha ve bee n de scribed. 24,38,39 The se assa ys m easure the ability of a
macrophage to ingest particulate substances, such as plastic beads or iron filings, and can be
perform ed on p erip heral blood or sing le cell susp ension s of ly m pho id organs, su ch as th e sp leen.
Other assays measure the capacity of the macrophage to destroy live bacteria through lysosomal
enzym e ac tivity. 40
iv) Stem C ell Assays: Bone marrow preparations can be used to investigate the pluripotent
pop ulation or sp ecific p rogenitor p opu latio ns. 41 Although these assays have not been used
extensively in imm unotoxicity evaluations, they may be recomm ended when histopathological
evaluation indicates that the test substance may have caused changes in bone marrow.
5. Type 2 Immunotoxicity Tests
Eva luating the functiona l capac ity of the im mu ne syste m re quires injec ting a sub stance that elicits
imm unological reactivity in a test animal. Various antigens provide information about the types of immunity or
cells that may be involved in an immune response. For example, protein antigens usually elicit T-dependent
imm une responses with subsequent production of antibodies to the protein. Polysaccharides elicit T-independent
immune responses. Some antigens elicit cell-mediated immune responses, while imm unogens such as complex
bacteria and viruses may elicit humoral and cell-mediated responses. All of the antigens listed below have been
tested in rodents; when an antigen has been used preferentially with a particular rodent species, this is noted.
4 T-Dependent Test Antigens: One of the m ost widely used an tigens for rodents 2,7,8,9,10,24,30,42,43 and non-
rodents is sheep red blood c ells (SR BC). 1,4-9,30,34,35,42,44 For exa mp le, SR BC s have been w idely use d in
mic e in the P laque-F orm ing C ell Ass ay: 45,46 antibod y-produc ing splee n cell susp ension s are m ixed w ith
SRB Cs, placed on covered slides, and incubated; each antibody-producing cell causes a small, clear area
(plaque) to form on the slide; the plaques are then counted. Other T-dependent test antigens that have
been widely used include keyhole limpet hemocyanin 10 and bovine serum albumin.
4 T-Independent Test Antigens: Ficoll, a bran ched chain p olysac charide , haptena ted ficoll,
polyvinylpyrrolidone, and bacterial lipopolysaccharides have been used as T-independent test antigens
with m ice and rats. 47
4 Human V accines: Human T -dependent vaccines, such as tetanus toxoid, and the T-independent
vaccine con tain ing pne um ococcal polysa ccharide antigens have be en use d in both rats an d m ice. 48-50 It is
possible to com pare resp onses o f the test spec ies to the va ccine s with h um an respo nses, bec ause sta ndard
hum an sera are ava ilab le fro m FD A's Center fo r Biolo gics. 51
4 Tes t Antige ns for C ell-M ediated Imm une (C M I) Rea ctivity: Contact sensitizers such as
dinitrochlorobenzene (D NC B) have b een used to elicit delayed hype rsensitivity (DT H) responses as a
me asure of C M I in anim als. The se assa ys can be perform ed in rode nt 52 as w ell a s non-rodent sp ecies.
The DT H assays are economical and correlate well with decreased CMI and host resistance to infectious
agents in hum ans, 53 as w ell a s an im als. 54 The mixed-lymphocyte response (MLR ) assay, which uses
lym pho cytes from a differe nt strain , has bee n successfully use d to eva luate C M I in m ice. 2
4 Ho st Re sistance Assa ys w ith Infectious A gents: A nu mb er of bacte rial strains hav e bee n used to
measure host resistance, including Listeria monocytogenes, various strains o f Streptococcus, and
Escherichia coli. 54 Useful viral mod els 55,56 include influe nza, he rpes, and cy tom egaloviru s. 57 A yeast
infectivity model using Candida albicans has been described, as well as parasitic infectivity models using
Trichinella spiralis and Plasmo dium yoelli.55,58
000239

4 Ho st Re sistance Assa ys U sing Sy ngen eic T um or Ce lls: Various assays of host resistance have been
described using a nu m ber of cultu red tum or cell lines. 58,59 These assays, unlike those involving the infectious
agents discussed above, do not require special barrier facilities to prevent infections from spreading throughout an
a nim a l c olo ny . T w o m o use assa ys h av e b ee n v alid ate d: th e P Y B6 sa rc om a assa y a nd th e B 16 F1 0 m e la no m a
assay.60 An a ssay usin g a lung tum or m odel an d the M AD B1 06 tum or cell line a lso has be en valid ated for use in
im m uno toxicity stud ies. 61
6. Relevance of Primary Indicators of Immune Toxicity to Health
a. Hematological Indicators
Hem atologic screens recommended for toxicity studies are basically the same as those performed
clinically as human health screens. Depressed or elevated WBC counts may be indicative of direct or indirect
effects of the test substance on cellular proliferation and distribution. Total WB C cou nts are used clinically as a
presum ptiv e test for infe ctio n; they are also use d to eva luate th e se verity o f an infla m m atory or alle rgic process.
Ro utine differen tial W BC counts a re used to differentiate a mo ng som e types o f infections a nd inflam ma tory
responses; they also are used as a screen for toxicologic or pharmacologic effects: for example,
immunosuppressive drugs may cause lymphopenia.
Altered lymphocyte counts may be relevant to imm unodeficiency. Increased numbers of
polym orphon uclea r leukoc ytes ca n result from pathog enic infe ctions an d from pyroge nic and inflam ma tory
processes. Eosinophilia is often associated with allergenic processes. It may also indicate an infectious, reactive,
or neoplastic process. Altered red blood cell counts and platelet counts can be associated with autoimm une
processes.
b. Serum Protein Indicators
Estimates of total serum proteins and the albumin/globulin ratio may give useful information about liver
and lymphocyte function. The "- and $-globulins (i.e. "- and $-G) are p rima rily produc ed in the liver; J-G are a
product of the B-lymphocytes. Depressed $-G lev els could lead to de crease s in com plem ent protein s that are
required fo r phago cytosis; this co uld produ ce de crease d resistanc e to bac terial infection s. Red uced levels of J-G
also cou ld m ean red uced levels of an tibodies n ecess ary for hum oral im mu nity to infectio us age nts. Altered levels
of J-G m ay indicate an effect on B -lymphoc ytes, T-lympho cytes, or simultaneous effects on both types of cells.
Ho we ver, total globu lin levels do not give sp ecific inform ation ab out w hich im mu noglob ulin classe s are
affected. Thus, when globulin levels are reduced, specific quantitative assays for the J-G subclasses may be
re co m me nd ed . E le ctro ph ore tic an d im m un oe le ctro ph ore tic an aly se s o f th e se ru m J-G subclasses or quantitative
assays such as Enzyme-Linked Imm unosorbent Assay (ELISA), Radioimmunoassay (RIA), or radial
imm unodiffusion may be recomm ended. This information may be important because reductions in J-G and J-M
may be relevant to infection by opportunistic and pathogenic organisms, and changes in J-A m ay indic ate effec ts
of the test substa nce on sec reto ry im m unity, su ch as gut-m ediate d im m unity.
c. Histopathology Indicators
Abnorma l results from gross and histological evaluation of the lymphoid organs (usually the spleen,
thymus, and lymph nodes) are important indicators of various immunotoxic effects; histological evaluation of
Peyer's patches and bone marrow also is recomm ended in screening for effects of a test substance on the imm une
system. Atrophy of the thymus gland with associated depletion of cortical thymocytes could be an indication of
imm unosuppression. Concomitantly, a similar effect on the lymphocytes in the periarterial lymphocyte sheath of
the spleen (PALS) would indicate an effect of the test substance on T-cells: both cell-mediated and humoral
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imm unity ca n be affec ted. In the splee n and ly mp h node s, defined reg ions are m ore den sely pop ulated w ith
B-lymphocytes, with activated, antibody-producing B-cells, or with plasma cells. Effects on B-cell regions of
these org ans co uld be a n indication of im mu nosup pression o r imm unoe nhan cem ent, depe nding o n the resu lt
obtained.
d. Bod y and O rgan W eights
Bo dy and organ w eights are genera lly recorde d during to xicity studie s. Spleen we ights are us ually
recorded in all toxicity studies, but thymus weights may not be recorded in long-term studies. The thymus gland
grows rapidly in young animals but begins to involute as the animals reach sexual maturity. In old animals, the
thymus ma y be difficult to detect and measure because of the degree of involution.
Organ weights by themselves or in relation to body weights can be sensitive measures of organ atrophy or
hypertrophy, but yield little information about immunotoxic effects. Reduced organ weights can result from direct
effe cts on ly m pho cyte proliferation and diffe rentiation a nd m ay be relevant for assessing im m uno sup pressio n.
Hype rtrop hy o f the lym pho id organs is usually associate d w ith in crease d prolife ratio n of cells (hype rpla sia).
Increase d proliferation of lym phoc ytes ca n result from infections, stim ulation by xenob iotics, altered m etabolic
processes, and certain forms of trauma, reactive, or autoimm une processes. In practice, however, changes in organ
we ights or orga n-to-body -weig ht ratios are m ore releva nt to im mu ne toxic ity wh en they are asso ciated w ith
appropria te histopathology findings.
7. Adequacy and Reliability of Primary Indicators of Immune Toxicity
If all prima ry indicators of possible immu notoxicity from toxicity studies are negative for a test
substan ce, w ould this effe ctively rule out the po ssibility that the te st substan ce prod uces sig nificant im mu notoxic
effects? T he ans we r to this question is com plex; som e of this com plexity de rives from the fact tha t the prim ary
indicators of possible immune toxicity listed above are not sufficiently specific or sensitive to provide
unam biguou s answ ers. For exa mp le, it is not possible to d ifferentiate B -lym phoc ytes from T-lym phoc ytes in
routinely stained sections of lymphoid tissues, and standard hematology tests cannot distinguish among
subcategories of T-lymphocytes. Special immunochemical stains, however, permit B- and T-cells to be visualized
in tissue sections and blood sm ears, making av ailable more inform ation about the imm unotoxic effects of the test
sub stance.
If only short-term toxicity studies are performed on a particular test substance, concern about the
adeq uacy and reliab ility of the im mu notoxic indicators from these stud ies m ay be h igh. Subtle imm unotox ic
effects or immune toxicities that develop only after prolonged administration of the test substance may not be
detec ted in sho rt-term tox icity studies. C onditions of the long er-term toxicity stud ies, how ever, m ay m ake it
difficult to detect som e imm une toxicities: the use of barrier facilities is comm on in carcinogenicity studies;
because barrier facilities limit exposure of test animals to exogenous infectious microorganisms, detecting
possible imm unotoxic effects of a test substance in carcinogenicity studies m ay be com promised be cause
spontaneous infection rates and mortality are evaluated as primary indicators of possible immunotoxicity in such
studies.
Eve n with this disadv antage , man y investig ators and regulatory authorities rec om me nd spe cific tests to
identify and cha racteriz e im m une system toxicities o nly wh en scre ening tests or in dicators are po sitiv e. 6,11
Additional rationale for this approach com es from the fact that m ost short-term toxicity studies incorporate at least
one do se in the p otentially h ighly toxic dose ran ge. Ad ditional tests for im mu notoxic ity should b e perform ed to
verify positive immunotoxic effects noted during screening studies or to determine if the positive result obtained
for a primary indicator was a false positive indication of imm unotoxicity. For example, certain test substances
may cause increased or decreased food intake; nutritional deprivation from significantly decreased food intake has
been shown to cau se th ym ic and splenic atrophy . 62 Effects on the endocrine system, such as stimulation of the
production of growth hormone 63 or prolactin 64 and dec reased levels of adrenoc ortic oste roid s, 65 can stim ulate
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grow th of the thym us. In respons e to such stimu li, involution of the thym us m ay proc eed a t a different rate in
animals exposed to the test substance than in control animals. Therefore, measuring thymic weights at one
specified time in a short-term toxicity study could give false positive or false negative indications of the test
com pound's imm unotoxic potential. For this reason, the Agency recom me nds that a study of the effects of a test
substance on thymic growth and involution be conducted at two or more time points during the study (such as
mid term and final sa crifice). Be cause sex differen ces ha ve bee n dem onstrated for various im mu nologic
studies,30,66 both sexes should be include d in imm unotoxicity evaluations.
There are data which suggest that the primary indicators do not evaluate toxic effects on all types of
imm une-related cells. Recent studies have shown that NK cell function may be affected without concomitant
effects on either B- or T-lymp hocytes.61 Other studies have shown that functional defects of specific lymphocytes
can oc cur w ithout app arent ch ange s in the prolifera tion or m orpholo gy of the c ells as obs erved in standard
histopathology preparations:11,67,68 the morphology of the cells is normal and a false negative result would be
obtained in these instances.
8. Recommendations for Further Immunotoxicity Testing when Primary Indicators of
Immunotoxicity are Positive
Assessing the safety of food and color additives used in food usually requires the completion of various
toxicity studies. In addition to the screen of primary indicators of possible imm unotoxicity provided by these
toxicity studies and summ arized above, additional tests for further evaluating the im mun otoxic potential of a test
substance may be recomm ended by the Agency. In the sections that follow, the adequacy of primary indicators of
imm unotoxicity for test substances that have been assigned to each Concern Level will be discussed. The
Agency's recommendation that specific immunotoxicity tests be performed on test substances that have been
assigned to Conc ern Le vels I, II, and III will be m ade on a ca se-by-case basis.
a. Immunotoxicity Stud ies for Compound s that ha ve been Assigned to Con cern L evel III
Test compounds that have been classified as Concern Level III substances present the highest level of
concern about their safe use as direct food additives and color additives used in food. When these substances
und ergo toxicity te sting, prim ary im m uno toxicity indicators may be n egativ e, m arginal, or positive.
Immunotoxicity tests suitable for each of these situations will be discussed below.
i. Immunological Tests when Primary Indicators of Imm unotoxicity are Negative or Marginal
If the primary immunotoxicity indicators from recomm ended toxicity tests are not positive, then no
additional tests for the imm unotoxic potential of the Concern Level III test compound would be recomm ended
unless the re we re spec ial circum stance s. Such c ircum stance s m ay inclu de: 1) the rod ent strains e mp loyed in
toxicity testing were highly inbred and are know to be resistant to imm unotoxic effects; 2) barrier or other
facilities were used for long-term and short-term toxicity studies, which m ay have preclud ed exposure of the test
animals to normal infectious agents present in the environment; and 3) omissions from the recomm ended guideline
for standard toxicity tests, such as not measuring thymus weights during the growth phases of the test animals or
om itting histopa thologica l analysis o f certain lym phoid o rgans. In these situations, som e Ty pe 1 im mu notoxic ity
tests and a Type 2 imm unotoxicity study of host resistance may be recomm ended, particularly if specific tests for
imm une toxicity had not been inco rporated into subchronic toxicity studies.
ii. Imm unological Tests when Primary Indicators of Immunotoxicity are Positive
W hen an y of the prim ary indica tors sugge sts that a C once rn Lev el III test substanc e has a n im mu notoxic
effect, addition al testing w ill be recom me nded in order to ass ess the e xtent of risk to the imm une sy stem . In
addition, positive effects on other target organs may indicate the need to assess the autoimm une potential of the
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compound.
Certain indicators may derive from effects on either B-cells or T-cells, or may be derived from effects on
both type s of cells. Ho we ver, m ost of the prim ary indica tors of im mu ne toxic ity are non discrim inating w ith
respect to specific lymphocytes involved and specific imm une functions affected. Standard histopathology
evalua tion m ay prov ide som e clues if there is an effec t on the thy mu s or if areas in the spleen o r lymp h node s are
associa ted w ith specific ty pes of lym phoc ytes. The objective s of expa nded Lev els I and II im mu notoxic ity tests
are to delineate the specific cells type(s) which are affected, to evaluate the extent to which specific imm une
functio ns a re im paired , and to relate these e ffec ts to risks such as in fection , hyp erse nsitivity , and carcinoge nicity.
The imm unotoxicity tests described in the following sections are for use with rats, and all tests should be
conducted on each test animal. However, tests have been, or can be, adapted for use with mice or non-rodent
species. W hen mice are used as test animals, serum from anim als in each experimental group may need to be
pooled if there is an insufficient quantity of serum from each anim al to perform recom me nded hem atology tests.
a) Re trospectiv e Le vel I Te sts: No a dditional a nim als are ne eded for Re trospectiv e Le vel I
imm unotoxicity tests when at least 10 animals of each sex are used in a standard toxicity study and
appropriate sam ples of blood and tissues are properly treated and preserved. After rem oving blood cells,
serum samples should be prepared by high-speed centrifugation, sterilized by filtration, and stored at 4-
5oC in sealed containe rs. At least half of eac h lym phoid tiss ue /organ should be fixed briefly in Bouin's
fixative (or other fixative shown to be appropriate) and stored in alcohol; sections from the tissue/organ
can be processed for histopathological analysis by routine staining or by im m uno stainin g.
If the standard toxicity study was a subchronic or chronic study (with exposure to the test substance for
90 to 120 days), and primary indicators suggested that the test material may be im munotoxic, the following
Retrospective Level I tests should be performed on serum sam ples from the study:
i) Electrophoresis of serum p roteins.
ii) Qu antification of serum imm unoglo bulins (IgG , IgM, IgA , IgE).
iii) Imm unosta ining for B - and T -lym phoc ytes in sple en and lym ph nod es and mic rom etric
analysis of the numb er of stained cells in specific regions of these organs.
iv) Scree ning for seru m a utoantibo dies to D NA , mitoch ondria, and other ce ll com pone nts
in one or more tissues, such as liver and smooth muscle.69 These tests should be performed
when there is an indication that the test substance may a ffect B- or T-lymp hocytes.
v) Imm unosta ining for bou nd IgG ma y be rec om me nded to determ ine if non-lym phoid
organ toxicities noted during the standard toxicity study (particularly a long-term toxicity study)
are due to an autoimm une reaction.
If the results of these Retrospective Level 1 tests demonstrate that the primary indicators of immune
toxicity were false positives, then no further imm unotoxicity testing would be recomm ended. However, if the
results of these tests are inconclusive or confirm an imm unotoxic effect of the test substance, additional testing
would be recom me nded. The ad ditional testing may include T ype 1 and T ype 2 im mun otoxicity tests.
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b) Ad ditional L evel 1 T ests: Additional Level 1 imm unotoxicity tests cannot be performed
retrospectively, but must be incorporated into the protocol of standard toxicity studies. How ever, all of
the tests de scribed in this section c an be p erform ed on th e sam e anim als that are u sed in the standard
toxicity study, provided that samples are processed appropriately. For example, half of the spleen can be
used to make a cell suspension for cellular analysis imm ediately following sacrifice of the test animal; the
rem aining h alf can b e proce ssed for histop atholog y evalu ation. Ad ditional (non -retrospectiv e) Le vel 1
tests that may be recommended include:
i) Qu antitative a nalysis of the B-ce ll to T-cell ratio (B /T) using either w hole blo od cells
and spleen preparations or spleen preparations only.
ii) Determination of spleen cellularity (the total number of white blood cells and
lymphocytes per gram of wet tissue) and the total number of viable cells per gram of wet tissue
or per million white blood ce lls.
iii) Assay of m itogenic stimulation for B- and T -lymphoc ytes:
iv) Analysis of N K cells using a suspen sion of spleen cells:
v) Determ ination of the phagocytotic index of m acrophages:
vi) Electrophoresis of serum proteins: Although this test can be performed retrospectively,
it is listed here be cause it is particularly use ful for evalua ting toxic im mu ne effec ts on liver,
ma crophages, and lym phocytes.
c) Lev el II Tests: If prima ry indicators of immu notoxicity from standard toxicity studies suggest
that a test co mp ound m ay be im mu notoxic , Leve l II tests ma y be rec om me nded to identify spe cific
functiona l imm une de fects. The se tests m ay be p erform ed on sa tellite groups of test anim als in
conjun ction w ith a stand ard toxicity study or the y m ay be p erform ed on te st anim als in a sep arate
imm unotox icity study. In the latter case , Leve l II tests should be perform ed w ith the sam e spec ies, strain
and age of test animals and the same doses of test substance used in the standard toxicity study of
com parable duration. In ad dition, sepa rate Le vel II im mu notoxic ity studies sh ould be 3 to 6 w eeks in
duration so that test animals will be exposed long enough to enable primary and secondary imm une
effects to be identified. An add itional period of time at the end of the study during which the test
sub stance is n ot adm inistere d w ould pe rm it ev aluatio n of the reversibility of observed im m une effe cts.
The following Level II tests may be recom mended:
i) Kinetic evaluation of primary and secondary immune responses of test animals to a T-
dependent antigen, such as SRBC , tetanus toxoid, or KLH ; serum antibody titers should be
measured following initial and secondary injections of the antigen.
ii) Evaluation of the primary humoral response to a T-independent antigen, such as
pneumococcal polysaccharides; choice of the optimum challenge dose should be justified.
iii) Evaluation of the delayed hypersensitivity response to a contact sensitizer during the second
half of the study. Alternatively, evaluation of the mixed lymphocyte response can substitute for
measurement of the DTH response as long as the assay has been validated with the particular rat
strain used.
d) Enh ance d Le vel II Te sts: These tests are designed to determine if a test substance that produces
imm une tox icity in Le vel I or Le vel II tests also a ffects host resista nce to c halleng e w ith infectious agents
or tumor cells. Enhanc ed Lev el II tests ma y be performe d with either rats or mice, because man y host
resistance tests have been validated in mice. These tests would be recomm ended in a variety of
circumstances; for example:
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i) If primary indicators of imm unotoxicity from standard long-term toxicity studies showed
increased mortality associated with administration of the test substance and effects on humoral
imm unity w ere iden tified from Lev el I and L evel II tests, then b acterial (e.g. Listeria
monocytogenes)58 or viral (e.g. Influenza )55 challenge tests associated with humoral immune
protection would be recomm ended for evaluation of host resistance.
ii) If there are indications that consumption of the test substance is associated with increased
tumorigenesis and effects on phagocytosis, tumor challenge tests with PYB6 sarcoma, which
tests cytolytic activity of T-cells and NK cells in mice,60 would be appropriate; a similar test for
rats uses the MAD B106 tumor line.61
iii) Finally, for test materials that have dem onstrated T-cell or cell-mediated im mun e effects,
challen ge tests tha t use certa in strains of Streptococcus 57 or Plasmo dium yoelli 58 would be
appropriate.
b. Immunotoxicity Stud ies for Compound s that ha ve been Assigned to Con cern L evel II
Specific imm unotoxicity tests generally are not recommended for test compounds that have been assigned
to Concern Level II. However, if primary indicators of possible immunotoxicity from toxicity studies conducted
on Concern Level II test substances are positive, additional Level I and Level II immunotoxicity tests may be
recom me nded; such recom me ndations will be m ade on a ca se-by-case basis.
c. Immuno toxicity Studies for C omp oun ds that ha ve been Assig ned to C oncern Lev el I
Usu ally, short-term acute e xposu re studies (up to 30 day s) are perform ed to ass ess the sa fety of C once rn
Level I compounds. Although guidelines for these studies (see Chapter IV C 3) do not rec om me nd spe cific
imm unotox icity tests, if prima ry indicato rs of possible im mu notoxic ity from short-term toxicity stud ies are
positive, ad ditional L evel I an d Le vel II im mu notoxic ity tests m ay be re com me nded . Such rec om me ndation s will
be made on a case-by-case basis. One imm unotoxicity test which measures the primary humoral response to the
T-depend ent antigen SR BC has been desc ribed for use with both rats 34 and mice 38 and has been recomm ended for
use in short-term screening studies.2
9. Animal Models for Immunotoxicity Tests
a. Ro dent M odels
These guidelines have focused on tests designed to assess immune toxicity in the rat. Specific strains
have been used and validated by the Agency, including Sprague-Dawley, Spartan,30 and O sborne M ende l; 69 the
Fisher 344 rat has been recom me nded by others 61 for studies w ith environ me ntal com pound s. Other strain s of rat,
such as the Buffalo strain, have been used in special studies to evaluate autoimmune disease potentiation.70-72 In
addition, several mouse strains (mainly inbred strains) have been used to assess immune toxicity.
b. No n-ro dent M odels
Use of the dog for various immunopharmacologic studies has been described in the scientific literature.73
Level I immunotoxicity tests described in these guidelines can be performed on most large animal species; Level
II immunotoxicity tests in other non-rodent models also may be acceptable, if validated: use of primates has been
described. 74 Also, miniature swine have been shown to be an excellent non-rodent species for evaluation of
variou s im m une functio ns. 75-79 The Age ncy ha s validate d a num ber of im mu ne func tion assay s for use w ith this
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mo del.
Imm unomodulation of porcine as well as other food animals have been reviewed.75 Other perspectives on
anim als sele ctio n ha ve bee n reviewed. 76
10. Recommended Strategy for Assessing the Immunotoxic Potential of Direct Food
Additives and Color Additives Used in Food
4 Primary indicators of imm unotoxicity should be evaluated for short-term (28-day) toxicity studies,
subchronic (90-day) toxicity studies, and developmental toxicity studies. Results of these evaluations
should b e incorp orated into an integ rated ass essm ent of the p otential for a te st chem ical to adv ersely
affect the immune system. Based on this assessment, an explicit statement should be made as to whether
or not the test chemical represents a potential immunotoxic hazard which requires further testing.
4 Additional studies to assess the imm une toxicity of food and color additives used in food will depend
on the results of the evaluation of primary indicators of imm une toxicity, the Concern Level to which the
additive has been assigned, and other information available concerning the imm unotoxicity of the
additiv e.
11. Conclusion
The hierarchical grouping o f recomm ended im mun otoxicity tests by specificity and mecha nics (e.g. tests
that use inje ctable substances) c an facilitate in cluding im m uno toxicity testing in sta nda rd toxicity studies.
Expanded testing on existing samples is possible, and allows for a more definitive identification of potential
imm unotox ic effects. Su ch exp ande d testing m ay be n ecess ary w hen ad ditional inform ation ab out a po ssible
im m uno toxic effec t is im portant for th e sa fety assessm ent of a direct food a dditive or color additiv e us ed in food.
Imm unotoxicity tests recomm ended in this section are summ arized in Table 1 below .
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Table 1
Summary of Immunotoxicity Testing Recommendations for Direct Food Additives
Ba sic Testing (Ra t M odel)
< CBC , WBC differential
< Total serum protein, albumin-to-globulin ratio (A/G)
< Histopathology, gross and microscopic (spleen, thymus, lymph nodes, Peyer's patches, and bone
marrow)
< Lym phoid o rgan an d body we ights
Retrospective Level I Testing: Included as a Possible Requirement in Standard Toxicity Study
< Electrophoretic analysis of serum proteins* (when positive or marginal effect noted in basic testing)
< Imm unostaining of spleen and lymph nodes for B and T cells* (quantification of total Ig)
< Serum autoantibody screen and deposition of Ig (micrometry for semi-quantitation of the proliferative
respons e)
Enhanced Level I Testing: Included as a Possible Requirement for More Complete Screening in the
Standa rd T oxicity Stud y Core Gro up, w ith a Satellite Animal G roup, or in
a Follow-Up Study
< Cellularity of spleen (lymph nodes, thymus when indicated)
- Quantification of total B and T cells (blood and/or spleen)
- Mitogen stimulation assays for B and T cells (spleen)
- NK functional analysis (spleen)
- Macrophage quantification and functional analysis (spleen)
- IL-2 func tional ana lysis (spleen )
< When indicated or for more complete analysis, other endpoints such as total hemolytic
complem ent activity or CH-50 assay with serum
Level II Testing: Includes a Satellite Group or Follow-Up Study for Screening of Functional
Immune E ffects
< Kinetic evaluation of the humoral response to a T-dependent AG (primary and secondary
respons es w ith either SR BC , TT, or oth er)
< Kinetic e valuation of the prim ary hum oral respon se to a T -ind ependent A G suc h as Pvax, TNP-
LPS, or other recognized AG
< DTH response to known sensitizer of known T-cell affecter
< Reversibility evaluation
Enhanced Level II Testing: Includes a Satellite Group or F ollow-U p Study F or Eva luation of
Potential Immu notoxic Risk
< Tum or challe nge (M AD B1 06 or othe r with the rat; PY B6 sarcom a w ith a m ouse m odel)
< Infectivity challenge (Trichinella, Candida or other w ith the rat; Listeria or other with the mouse)
_________________________________________________________________________________________
Abb reviations: CBC = complete blood count; WBC = white blood count; Ig = immunoglobulin; NK = natural
killer; IL-2 = interleukin-2; SRBC = sheep red blood cells; and TNP-LPS = trinitrophenol
lipopolysaccharide.
* Recom mended for inclusion in basic testing.
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Chapter V D: Immunotoxicity Studies - References
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pneu mo polysa ccha ride by rou te of injection of pertu ssis vac cine. Infect.Immun. 23(3):675-680.
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52. Godfrey, H.P. and G ell, P.G. (1978) Cellular and molec ular events in the delayed-onset hypersen sitivities.
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53. M aclean, L.D. (1979) H ost resistance in surgical patients. J.Trauma 19:297-304.
54. Bradley, S.G . and M orahan, P.S. (1982 ) Approaches to assessing host resistance. Environ .Health
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assessm ent of im m uno toxicologic effec ts. In, Imm unotoxicology and imm unopharmacology. (J.H. Dean,
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56. K ern , E .R . (1 98 2) U se of v ira l in fe ctio ns in an im a l m o de ls to asse ss c ha ng es in th e im m un e sy ste m .
Environ. Health Perspect. 43:71-79.
57. Selgrade, M.K., Daniels, M.J., Burleson, G.R., L. D. Lauer, L.D. and Dean, J.H. (1988) Effects of 7,12-
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Stu dies of re sista nce m echanism s. Int.J.Immunopharmacol. 10(7):811-818.
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Chapter VI
Human Studies:
This chapter presents general guidelines for the conduct of human clinical studies on foods and food
ingredients. It also describes the types of human epidemiology data that may be useful to the Agency in assessing
the safety of direct food additives and color additives used in food. Because hum an clinical studies were not
included in the 1982 guidelines for direct food additives and color additives used in food, important issues related
to these stud ies are disc ussed at le ngth in this cha pter.
The Agency does not require petitioners to conduct human clinical studies to support the safety of direct
food ad ditives an d color ad ditives use d in food. H ow ever, petition ers m ay elec t to perform such stud ies in certain
circumstances, such as when the proposed additive will be consumed by humans at relatively high levels (see
Cha pter V II B). W hen petitioners conduct human clinical studies on substances intended for use as direct food
additives and color additives used in food, however, the Agency recomm ends that the studies conform to the
guideline s presen ted in this sec tion. As us ual, the A genc y strongly re com me nds that p etitioners pla nning to
cond uct hum an studie s in suppo rt of the safety o f direct food a dditives a nd colo r additives u sed in foo d cons ult
with the Agency before the studies begin.
VI A. Clinical Evaluation of Foods and Food Additives
A m ajor objective in the clinical testing of food and food additives is to assess aspects of safety that
cannot be addressed adequately by non-human studies or by existing data on population exposure. For example,
the Agency is now confronted with petitions for direct food additives that are intended to substitute for major
nutrients such as fat and sugar. Because segm ents of our population ma y be exposed to large quantities of these
additives for long periods of time, traditional methods of evaluating the safety of these substances may not be
adequate. Testing these substances in animals at doses that greatly exaggerate their anticipated human exposures
may not be possible. For these substances, human clinical studies may provided additional confidence in the
safety of the food or food additive.
A foo d or food a dditive ge nerally w ill be cons idered su itable for clinic al testing if the su bstanc e is
unlikely to produce significant toxic effects at the levels to which the subjects of the clinical study will be
expo sed. Th is usually is de term ined from the results of tox icity studies in anim als or by ex am ining ex isting data
on pop ulation ex posure. H ow ever, in ca ses w here the type of tox ic respon se assoc iated w ith the con sum ption of a
food or food additive by experimental animals is judged to be severe, exposure of subjects in clinical studies to the
additive ma y need to be significantly below the level found to produce no toxic effects in an appropriate species.
Unlike patients participating in clinical trials of new drugs, no health ben efit is anticipated for most test
subjec ts in clinical stud ies of foods a nd food additives . Thus, the n ature an d we ight of evid ence required to
establish th e safety o f these prod ucts for hum ans be fore clinica l studies ca n begin ma y differ from that required to
suppo rt testing unde r guideline s for investiga tional new drugs. C linical studie s of foods an d food a dditives w ill
focus on demonstrating safety; for example, the safety of an additive that may interfere with absorption of
nutrien ts, w hos e sta tus in the po pulatio n is u ncerta in, m ay nee d to be e valuated in a clin ical study.
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1. General Considerations for Clinical Studies of Foods and Food Additives
Principle s for the con duct of clin ical trials are co ntained in the M ay 8, 197 9 Fed eral R egister: "Statement
concerning adequate and well-controlled clinical investigations." 1 The following guidelines identify general
considerations for clinical studies of foods and food additives. Each consideration should be explicitly addressed
in the clinic al study 's protocol.
4 Be fore unde rtaking co stly and tim e-cons um ing clinica l studies as p art of the safe ty assessm ent of a
food or food additive, the investigator needs to formulate a defensible rationale for conducting human
clin ical studies an d a c lear set of ob jective s.
4 Ad equate preclinic al in vestigatio ns (including toxicity tests in a nim als) m ust h ave be en com pleted.
Re sults of these tests m ust establish that there is no expec ted toxicity to m an at do ses to be used in
clinical stud ies. A cle ar, concise description of the desig n of pre-clinic al studies a nd their resu lts should
be presented to FDA. Information about the history of use of the food or food additive outside the United
States and documentation of the results of foreign clinical studies involving the food or food additive
sho uld also be p rese nted for review .
4 In designing protocols for clinical studies, the following should be considered: 1) the results of pre-
clinical studies (including toxicity tests in animals) and foreign clinical studies; 2) the chemical nature of
the proposed additive; and 3) all organs and organ systems that may be affected in man by consumption
of the food or food additive under investigation.
4 Th e se que nce of clin ical tests should be des igned to m axim ize the safe ty of the rese arch subjects.
4 Guidelines for clinical trials of investigational new drugs should be followed in evaluating the
qualifications of the principal investigator and investigating institution. In particular, careful
consideration must be given to the qualifications of the investigator and the suitability of the investigating
institution's facilitie s for c ond ucting short- an d long-term clin ical trials.
FDA recognizes the need for the investigator to exercise sound clinical judgement based on his/her
experience in an appropriate field of study. Studies involving healthy volunteers should be performed by
investigators skilled in the evaluation of the safety of a variety of compounds. W hen subjects of a clinical study
have a specific disease, as may be the case for clinical evaluation of foods for special dietary uses or special
m edical purposes, the investigators should be c linic ians ex pert in th e disea se a nd d isease process.
4 The investigator should have high regard for the rights and safety of the test subject(s). The
investiga tor is responsib le for the ad min istration of the foo d additive ; thus, he/she mu st bear the ultima te
respons ibility for the w elfare of the test subjec ts. All aspe cts of a clinic al study g enerally are desc ribed in
the study's protocol; however, because actions that have been identified as being in the best interests of
the subjects at the beginning of a clinical study m ay change during the study, all aspects of the study must
remain flexible and subject to modification. Aspects of the clinical study protocol subject to such
modification include: 1) The nature and frequency of laboratory tests, 2) the duration of consumption of
the food or food ad ditiv e, an d 3) the inte rval between test subjects' visits to the investigator.
Institutional rev iew of researc h involvin g hum an sub jects and the require me nt for inform ed con sent w ill
provide additional safeguards for test subjects. Principles of institutional review and informed consent were set
forth in the M arch 13 , 1975 Fe deral R egister: "Technical Am end ments Conc ernin g Protection of Huma n Su bjects;"2
these are summarized in Appen dix A (see sec tion V I A 5 be low).
4 There is some finite risk associated with the administration of every unapproved food and food
additive to subjects of a clinical study; despite strict adherence to guidelines, the safety of subjects in the
study cannot be guaranteed. Before beginning a clinical study, the investigator should consider what
procedures will be used to detect adverse reactions to the test substance during the study. The
000254

investigator should establish criteria that will be used to decide when to discontinue the clinical study;
these criteria may be changed during the study if the change is required to support the safety of the
sub jects.
To further protect the safety of subjects of a clinical study, the sponsor of the study should provide
appropriate follow-up after the study has ended. Such follow-up should be conducted or supervised by the
investigator of the clin ical study.
4 Before a clinical study begins, the investigator should consider ways in which quality control of the
study will be documented. Effective documentation of quality control will facilitate Agency review of
the com pleted clin ical study.
4 FDA recomm ends that investigators use statistical expertise in the planning, design, execution, and
analys is of pre-clinica l and clinic al studies. Su ch exp ertise w ill help ensu re that the p lanned studies w ill
provide the necessary information while minimizing the number of subjects (sample size estimation) and
will strengthen the validity of estim ates of safety obtained from the stud ies.
2. Specific Considerations for Clinical Studies of Foods and Food Additives
This section describes specific considerations concerning the protocol design, definition of study
population, and statistical analysis of the results of human c linical studies with foods and food additives. These
consid erations sh ould be explicitly a ddresse d in the clin ical study protocol.
a. Protocol Design
Protocols for clinical studies of foods and food additives should be described clearly and in sufficient
detail to pe rmit effe ctive rev iew and ev aluation by C FSA N. In gen eral, the protoc ol should be strictly ad hered to
through out the c linical study ; if the protoco l is not adhe red to, docu me ntation of n ecessary m odification s should
be m ade (se e item 7 in section 1 abov e). W hile it is rational an d desirab le to desig n studies to obtain sp ecific
inform ation ab out the tes t substanc e, the gen eration of d ata justifying conclu sions othe r than those originally
anticip ated ca n be a va luable resu lt of c linic al in vestigatio n.
The following are additional recomm endations for the design of clinical study protocols for foods and
food additives:
4 A clear statement of objectives should be provided for each protocol. Good planning usually produces
researc h ques tions that ca n be an swe red by d irect inferenc e from the study data. Sinc e studies a re
frequen tly design ed to an swe r mo re than on e ques tion, it is useful to list the que stions to be answ ered in
order of their priority.
4 The rationale for conducting a clinical study should be presented. In addition, pre-clinical and clinical
data relevant to the compound being studied and to the proposed protocol should be reviewed.
4 A statement explaining the reasons for deciding on a particular length for the clinical study should be
included in the protocol. In general, a clinical study should be of sufficient length to permit the
demonstration of the safety (or lack of safety) of a food or food additive.
4 A statement explaining the reasons for selecting particular dietary levels (dosages) of the food or food
additive being tested should be included.
4 Experimental design should include appropriate controls. When feasible, studies should be performed
blind to avoid selection bias and bias in patient and physician respon ses.
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4 Investigators should describe proposed methods of randomization and should present analyses that
dem onstrate the effectiveness of these method s.
4 Obje ctive ob servation me thods sho uld be u sed w hen po ssible and approp riate, observa tional end points
should be rigorously defined, and methodology that will be used to quantify endpoints should be
described. A statement describing quality control and frequency of data collection (endpoint monitoring)
also should be included.
4 Limitations that may be imposed on the clinical study because of protocol design or the failure of
subjects to comply with the written protocol (such as withdrawals from the study, failure to randomize
sub jects effective ly, technological lim its of observ atio ns, etc.) and the possible effects these limitations
may have on the outcome of the study should be addressed.
b. The Study Population
Clinic al studies id entify p hys iolo gical re spo nse s to te st substa nces in we ll-de fine d, sm all p opu latio ns.
These results are used to make inferences about responses to the test substance in larger, target populations. Study
protoco ls should sp ecify ho w su bjects w ill be selec ted, their assign me nt to alterna tive test regim ens, the spe cific
conditions under wh ich the trial will be conducted, and the nature of the target population to which the subjects'
respons es w ill be extrap olated. T he follow ing are a dditional re com me ndation s for defining a nd selec ting subje cts
for the clinical study:
4 Each study protocol must be reviewed and approved by the appropriate Institutional Review Board;
written, informed consent must be obtained for each subject in the study (see Appen dix A in section VI A
5 be low ).
4 Protocols should clearly define the selection criteria for subjects, including diagnostic criteria and
reasons for exclusion from the study, and should compare and contrast the study population with the
larger population likely to consume the food or food additive.
4 Criteria for discontinuing the study should be stated clearly.
4 Doses of the test substance should be selected so that a range of subject responses to the substance can
be observed and the highest safe dose of the proposed additive can be determined. When individual
subjects' responses are expected to be quite variable, testing at multiple doses in a double-blind,
placebo-controlled study is recommended.
4 A serious problem in clinical studies is determining the degree of subject adherence to the assigned
protocol. Careful attention to subject compliance with the protocol is particularly important in outpatient
studies. Proto cols sho uld state c learly how subjects' com pliance will be m onitored a nd shou ld indicate
when noncompliance will result in discontinuing the subject in the study. In general, data on subject
compliance and noncom pliance enhance the credibility of a study.
If it becomes apparent during the study that subjects are not complying with the study protocol, reasons
for their noncompliance should be determined. All subjects initially included in a study must be reported on in the
study's results, regardless of the degree of their compliance. Some noncom pliance may necessitate identifying
subgroups for evaluation, such as subjects who fail to consume foods containing the additive and subjects who
report excessive use of alcohol or medication.
4 The num ber of subjects to be included in the study should be sufficient to be able to determine the
safety of the test substance. Statistical estimates of the required number of subjects will depend upon: 1)
The de sired limit of detection of subjects' responses to the test substance; 2) the desired assurance ag ainst
a false positive resu lt; an d 3) the acc eptable risk of a false neg ativ e result.
000256

4 W hile it is desirable that placebo groups be included in early clinical studies of proposed foods and
food ad ditives (see page 1 7), this is not a requ irem ent. Go als of early c linical studie s m ay be 1 ) to
gradua lly increase the dose of the test sub stance until physio logical e ffects are ob served or 2) to
determ ine abso rption and me tabolism in hum ans in an effort to assess th e ade quac y of anim al m odels
used in safety assessments of the test compound. Therefore, subjects must be under careful observation
during these studies.
The goals of early clinical studies often can be achieved effectively with an open (non-blind) study
protocol. W hen clinical studies using blind comparisons of the test substance and a placebo or positive control
substance should begin varies with the nature of the test material. During all phases of clinical investigation, the
objective in using a placebo is to provide an adequate control for the compound under study. However, other
methods of adequately controlling clinical studies exist. For example, the use of an active control compound or
d em o nstra tio n o f a po sitiv e d ose re sp on se to th e fo od or fo od ad ditiv e m a y c on stitu te ad eq ua te co ntro l in so m e
studies. For situations in which the natural course of a disease or condition is predictable and for which objective
me asurem ents of thera peutic o r prophyla ctic respo nse to the test com pound can be ma de, results of ca refully
executed, open (non-blind) studies may be compared to historical data.
4 Food additives should be studied in all age groups that may be significantly exposed, including, as
approp riate, children, w om en of ch ildbearing potential, olde r populatio ns, and po pulations with sp ecific
disease conditions. The latter category includes populations that may be particularly exposed to,
positively affected by, or at risk from a particular food or food additive.
Pregnancy tests should be administered to women of childbearing potential before the introduction of the
test substance and the subject should be advised about suitable contraceptive measures. In general, wom en of
childbe aring pote ntial shou ld be ex cluded from th e earliest c linical studies of a test sub stance . Once an ade quate
baseline of clinical information about the safety of a food or food additive has been obtained, however, wom en of
childbearing potential may be included in clinical studies. For example, women of childbearing potential may
participate in clinical studies when the teratogenic potential of the test substance has been determined to be
negative in anim als.
Follow-up to detect possible effects of the test substance on the fetus should be provided to women w ho
beco me pregna nt wh ile on the stu dy. Un der these circum stance s, transplace ntal passa ge of the su bstanc e and its
secretion in milk should be assumed until proven otherwise.
4 If the proposed food or food additive has a significant potential for use in children, its safety should be
evalua ted in ch ildren. Usu ally, studies in c hildren are not attem pted un til there has b een c onside rable
clinical ex perienc e w ith the add itive in adu lts. For certain pro posed food ad ditives, how ever, early
clinical study in children may be warranted; in such cases, it is preferable to begin with older children,
follow ed by y ounge r children, infan ts, and prem ature infan ts. Detailed com me nts on pe diatric studie s are
contained in "General Considerations for the Clinical Evaluation of Drugs in Infants and Children."3
Additional examples of guidelines concerning the clinical testing of foods or food additives in children
are provided by the A me rican Acad em y of Pediatrics.4,5
4 Gen erally, physic al exam inations a nd labo ratory tests sho uld be p erform ed to scre en indiv iduals w ith
medically significant abnormalities from the clinical study. Laboratory tests should include the
follow ing: 1) Ele ctrocard iograph ; 2) urinalysis; 3) va rious tests on b lood sam ples (for exa mp le, com plete
blood counts including platelet estimates, blood urea nitrogen, serum creatinine, tests of liver function,
fasting blood sugar or 2-hour postprandial blood sugar, electrolytes, protein, and albumin); and 4) other
tests that may be indicated by the nature of the test compound or from the results of previous animal and
hum an clinic al studies (for ex am ple, tests of vitam in status, prothrom bin tim e, and blo od lipid profiles ).
4 In early clinical studies, when feasible, all subjects should refrain from taking medication (including
over-the-counter drugs) for at least two (and preferably four) we eks before the study begins, unless
interactions of the test substance with medication are the focus of the study. In some cases, a longer
"w ash out" pe riod will be require d for retu rn to a no rm al phys iolo gic state be fore the clin ical study b egins.
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In later clinical studies, it may be desirable to examine the safety of combinations of the test substance
and m edica tion(s).
4 Post-study physical examinations for subjects of clinical studies often are necessary to ensure the
subjects' safety. The results of these examinations should be fully documented.
c. Statistical Analyses
The following are general recommenda tions for statistical analyses in clinical studies of foods and food
additives. Additional recommenda tions are contained in Chapter IV B 4.
4 Investigators are encouraged to seek expert biostatistical assistance prior to formulating the study
design.
4 A priori description of the statistical m ethods to be use d in ana lyzing d ata from a clinica l study sho uld
be prov ided in the study's protoc ol.
4 Estim ates of statistica l pow er should be use d to help d eterm ine the o ptim al num ber of subje cts for a
clin ical study.
3. Sequence of Clinical Studies for Foods and Food Additives
The rationale behind serially conducted studies is that results of each study may influence the plan of
succeeding studies. Investigators are encouraged to discuss data from animal studies and early clinical studies
with C FSA N before con ducting additional clinical studies.
a. Early Clinical Studies
The purpose of these studies is to determine the metabolism and the level of the food or food additive that
gives an adverse or toxic response in man. Physiologic processes that are of primary interest in early clinical
studies inc lude: 1) D isposition (ab sorption, biotran sform ation, and excretio n) of the food or food ad ditive and its
metabolites; 2) the potential of the food or food additive to induce enzyme levels or increase activity; 3)
interactions between the food or food additive and nutrients that may necessitate balance studies; and 4)
interactions between the food or food additive and medications that may necessitate drug bioavailability or drug
metabolism studies. Information about the potential use of the test substance and all preclinical information about
the test substance should factor into decisions about the appropriate sequenc e of early clinical studies.
For both ethical and scientific reasons, the initial introduction of a food or food additive into humans
should be done w ith carefully selected subjects. Subjects for early clinical studies should be "norm al" volunteers.
"Normal" generally means volunteers who are free from health problems that would complicate the interpretation
of the study or increase the sensitivity of the subject to the toxic potential of the food or food additive. Children,
pregnant w ome n, and wom en of childbearing potential usually should be exclude d from early clinical studies.
W ithin the limitations described in the preceding paragraph, subjects of early clinical studies should be
selected to accurately reflect the general population. Thus, individuals with mild but stable illnesses such as
uncomplicated hypertension or arthritis may be considered for inclusion in initial clinical studies on a food or food
additive. It also may be permissible--and even desirable--to include subjects with abnormalities for which
consu mp tion of the foo d or food a dditive m ay be p articularly be neficial. For e xam ple, subjec ts with
hyperlipoproteinem ia may be included in an early clinical study on a food or food add itive that functions as a
non-caloric fat substitute. Additional examples include: (a) A food or food additive that will be used in the
dietary m anag em ent of orga n failure sho uld be te sted in a p opulation with failu re of the orga n unde r study; (b) a
food or food additive d esigne d to be de ficient in a pa rticular nutrien t should be tested in a p opulation that is unab le
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to m etaboliz e the nu trient in ques tion (in fact, such a food or foo d additive ma y be ha rmfu l to a popu lation w ith
norm al m etabolism ).
M ost early c linical studie s are sub-c hronic (rela tively sho rt-term) an d are ge nerally less than 4 w eeks in
duration. These studies vary from single exposure to multiple exposures and examine a range of levels (doses) of
the food or food additive. When several doses are being tested in a study, no research subject should be given the
next-higher dose until sufficient exposure has occurred with the imm ediately preceding dose to be certain that
serious adverse effects have not occurred.
For each food and food additive subjected to clinical investigation, it is also important to consider the
approp riate freque ncy of lab oratory tests a nd, wh en indic ated by the results of pre vious stud ies, tests for specific
organ or organ system effects. Independent of the outcome of clinical studies, thorough physical examinations and
blood screening should be part of the follow-up for all subjects.
W h en un an tic ip ate d sid e e ffe cts o cc ur in clin ic al stu die s, th e in ve stig ato r sh ou ld de te rm in e th e tim e
required for elimination of the com pound from the subject's system and reversal of the effects.
b. Further Clinical Studies
Additional clinical studies may be designed to determine the safety of the proposed food additive during
chronic intake (rela tively long -term) a nd to ga ther m ore inform ation ab out the foo d additive 's adverse e ffects in
humans. These studies should be performed after the general safety of the food or food additive in humans has
been establishe d in early, sho rt-term c linical studie s. The d uration of e xposu re to the food or food ad ditive in
these studies will vary with the nature of the additive. Chronic administration in humans usually means
continuous consum ption for at least 8 to 12 weeks, unless contraindicated by adve rse side-effects.
Relatively long-term clinical studies of food and food additives may emphasize the physiologic processes
of enzyme induction or interaction of the additive with other substances (such as nutrients, medications, and other
food additives). In addition, when designing studies to determine the safety of chronically consumed food
additives, investigators should consider conducting nutrient balance studies; these studies help determine
end-organ (or end-organ system ) responses to the additive, including neurobehavioral change s.
Finally, clinical studies may be performed to obtain information about adverse effects of the food or food
additive on specific subpopulations. For these studies, appropriate subpopulations may include children, pregnant
wo me n, wom en of ch ildbearing potential, an d older su bjects. Th ese stud ies m ay also in clude su bjects w ith
conc om itant disea ses w ho are u ndergo ing therap y for the dise ase, particu larly if such subjects rep resent se gm ents
of the po pulatio n w ho a re lik ely to cons um e the food o r food ad ditiv e after it has bee n ap proved.
Re latively lon g-term clinical stud ies shou ld include a limite d num ber of close ly m onitored su bjects
(rarely exceeding several hundred). In the clinical studies described above, the frequency of physical
exam ination s an d laboratory tests fo r sub jects w ill de pend u pon the nature and rela tive safe ty of the food ad ditiv e.
For som e subjec ts, daily supe rvision m ay be n ecess ary. Early p eriods du ring a study will typic ally involv e m ore
frequen t supervision of subjec ts than later p eriods. A n exam ple of a gra ded su pervision plan w ould be one in
wh ich a test su bject is see n by the investiga tor at least on ce a w eek for 2 to 4 we eks, onc e eve ry other w eek for 6
to 8 weeks, at monthly intervals for 2 to 3 months, and bimonthly until the end of the follow-up period. Routine
laboratory tests should be performed at frequent intervals; frequency and type of special laboratory tests should be
determined by the nature of the food or food additive and its intended use.
In both ea rly and ch ronic clinic al studies o f food add itives, it is particularly im portant tha t a single
formulation of the test substances be used throughout the study; in addition, investigators should test the
compounds that will be marketed. Consideration should be given to relative exposures for particular food uses
when such uses may alter the structure or effects of the test substance. A significant change in the formulation or
ma nufactu re of the food or food ad ditive during chronic clinical stud ies m ay indic ate the need for bio availab ility
studies on the (presumably changed) food or food additive. Results of these studies will enable meaningful
comparisons to be made among clinical studies performed with different formulations of the test substance. W hen
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the petitioner intends to market a family of formulations and only a limited number of the formulations will be
tested in c linical studie s, petitioners sho uld be p repared to dem onstrate tha t the test com pound s are fully
representative of the family of formulations intended for marketing, particularly with respect to questions of
safety.
4. Submitting Reports of Clinical Studies on Foods and Food Additives to CFSAN
In submitting reports of clinical studies to CFSAN , particular emphasis should be placed on clear and
concise: 1) statem ent of study objective s, 2) desc ription o f protocols, a nd 3 ) presen tatio n of sign ifica nt fin dings.
Presen tation of the re sults of a series o f clinical stud ies on an propose d food a dditive sh ould be scientifically
logical and should specify th e order in w hich the stu dies w ere con duc ted.
Early, relatively short-term clinical studies include tolerance studies. In reporting the results of tolerance
studies, information on dose schedules and range of doses should be included. For relatively short-term clinical
studies, the following questions should be answered in determining the safety of the proposed additive:
4 W hat are the absorption, metabolism, tissue deposition, and major routes of excretion of the food or
food additive?
4 W hat is the half-life of the food or food additive in the human body? (Analysis of turnover and of
other pharmacokinetic parameters of the test substance or its metabolites in various physiological
compartments may aid in the interpretation of the results of toxicity studies.) (see Chapter V B);
4 How may interactions between the food or food additive and nutrients or medications comprom ise the
availability of any of these substances?
4 How does the food or food additive affect the function of huma n organs and organ system s?
4 W hat are the possible adverse reactions to the food or food additive in the general population of
individuals who are likely to use the substance and in special (mo re sensitive) populations?
Reports on relatively long-term clinical studies should emphasize specific organ or organ system
responses to the food or food additive and nutrient imbalances that occur with chronic use of the food or food
additiv e.
Finally, the safety of a food or food additive may continue to be monitored after the substance has been
approved. This can be accomplished by further clinical testing or by establishing a surveillance system and
documenting adverse reactions to the food additive. The need for such a system is expected to vary with the
nature and use of the approved food additive. Clinical testing and surveillance also may be useful in establishing
the safety of expanded use s of the food or food additive or the safety of an altered food or food additive; these
changes may occur as the result of changes in patterns of food consumption or food processing.
5. Appendix A
The following principles are general guidelines for institutional review of, and conformed consent of
subjec ts for, clinical studies . Addition al inform ation ca n be fou nd in the re ference s for this chap ter.
a. Principles of Institutional Review
4 An Institutional Review Board must be com posed of no fewer than 5 persons from various
backgrounds to assure complete and adequate review of clinical research activities comm only conducted
by the institution. In addition to possessing the scientific competence necessary to review such
institutional activities, the Board must be able to evaluate research applications and proposals in terms of
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institutional commitments and regulations, applicable law, standards of professional conduct and practice,
and com mun ity attitudes.
4 No m ember of a Board shall be involved in the initial or continuing review of an activity in which he
has a conflicting interest, except to provide information requested by the Board.
4 No B oard shall consist entirely of persons who are officers, employees, or agents of, or are otherwise
associated with the institution, apart from their membership on the Board.
b. Principles of Informed Consent
All subjects in a clinical evaluation are entitled to:
4 a fair explanation of the procedures to be followed and the purposes of the procedures, including
identification of any pro cedu res that are e xperim ental;
4 a description of attendant discomforts and risks that may be reasonably expected;
4 a description of benefits they may reasonably be expected;
4 disclosure of approp riate alterna tive proce dures tha t ma y be ad vantag eous to th e subjec t;
4 an offer to answer any inquiries concerning the procedure; and
4 instruction that the subject is free to withdraw his consent and discontinue participation in the project
at any tim e, without prejudic e to the su bject.
References
1. Anonym ous (1979) Refusal to approve the application (21 CFR 314.111 Section A5ii) Statement
concerning ade qua te and w ell-c ontrolle d clinic al in vestigatio ns. Fed.Reg. (April 1) 107-110.
2. An onym ous (198 8) Protec tion of hum an sub jects (21 C FR Part 50) Fed Reg. (April 1) 215-229.
3. Health, E duc atio n an d W elfa re (H EW ) (1977) In, General considerations for the clinical evaluation of
drugs in infants and children. HEW , PHS, and FDA R eport. U.S. Printing Office.
4. Am eric an Ac adem y of Pediatrics Com m ittee on N utrition [AAPC N] (1988) In, Clinical Testing of Infant
Form ulas w ith Re spect to N utritional Su itability for Te rm Infa nts. Prepared under FDA contract
223 -86-2117. pp.1-36.
5. Am erican A cade my of Pedia trics Co mm ittee on N utrition [AA PC N] (198 7) Guidelines for the clinical
evalua tion of new produc ts used in the dietary m anag em ent of infan ts, children an d pregn ant w om en w ith
me tabolic diso rders. A report by the Ta sk Forc e on C linical E valuatio n of Prod ucts for M etabolic
Disorders. Prepared un der FD A con trac t 223-82-2393 . pp.1-53.
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October 2001
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
1. 	Descriptive Epidemiology Studies
a. 	Correlational Studies
b. 	Case Reports
2. 	Analytic Epidemiology Studies
a. 	Cross-Sectional Studies
b. 	Prospective Studies
c. 	Retrospective Studies
d. 	Meta-Analyses
3. 	Epidemiology Studies References
Epidemiology is the study of the distribution and determinants of health-related states and events in specified
populations, and the application of this study to the control of health problems.(5) The goal of all epidemiology
studies is to uncover relationships between exposure to a specific agent and changes in health status.
Epidemiologic data are important to CFSAN in assessing safety and have been used by the Agency as
indicators where avenues of research and further human studies would be most productive. Guidelines for the
proper conduct and documentation of epidemiology studies, such as selection of the study population,
selection of appropriate controls, exposure assessment, methods used to adjust or control for confounding
variables, and statistical analyses will not be discussed here. Appropriate guidelines have been published
elsewhere, (1) and should be consulted by the petitioner before submitting epidemiology data for consideration
by the Agency.
There are two main categories of epidemiology studies, descriptive and analytic. Descriptive studies are
concerned with the existing distribution of variables; they do not test hypotheses or make inferences
concerning causality. Analytic studies are designed to examine associations, particularly hypothesized causal
relationships, and focus on identifying or measuring the effects of specific risk factors.
Redbook 2000: VI.B Epidemiology
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter VI.B. Epidemiology
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: VI.B Epidemiology
Page 1 of 5	3/3/2010
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Descriptive epidemiology studies are relatively inexpensive to conduct and are usually of short duration.
However, such studies are limited in their usefulness since no inferences can be made concerning causality.
Generally, descriptive epidemiology studies are sentinel devices used to generate hypotheses or to provide
evidence that indicates whether there is sufficient cause for conducting a lengthier and costlier analytic study.
Correlational studies, also called ecological studies, use grouped population data to relate exposure patterns of
whole populations to disease incidence or mortality rates for whole populations. Because these studies do not
examine the relationship between exposure and disease among individuals, the studies have been traditionally
regarded as useful for generating, rather than definitively testing, a scientific hypothesis. Thus, the results of
correlational studies would be insufficient to demonstrate a relationship without other types of data to support
them.
Case reports are a type of descriptive epidemiology study frequently evaluated by CFSAN. Strongly suggestive
anecdotal or clinical observations may indicate a possible causal relationship. Analytic epidemiology studies
can then be designed to verify and quantify the risks, and to determine the role of confounding factors.
There are two principal avenues through which case reports come to the attention of CFSAN: first, reports
published in the peer-reviewed medical literature, and second, reports captured in one or more of CFSAN's
ongoing voluntary (also called "passive") adverse event monitoring systems, which include:
The Adverse Reaction Monitoring System (ARMS) - collects spontaneous reports from consumers and health
professionals regarding alleged adverse effects from food products.
The Cosmetic Adverse Reaction Monitoring System (CARMS)- collects spontaneous reports from consumers
and health professionals regarding alleged adverse effects from cosmetic products.
In addition, CFSAN receives adverse event reports linked to the products it regulates through FDA's
MedWatch 2 program. (4)
Although analytic epidemiology studies are more informative than descriptive studies, they are expensive and
time-consuming to conduct. The types of analytic epidemiology studies commonly considered by CFSAN in
safety evaluations include cross-sectional, prospective, and retrospective studies. Results from such studies,
when available, are used in the overall safety evaluation of regulated products. In addition, analytic
epidemiology studies constitute the scientific base for the Agency's regulation of health claims on food and
food labeling authorized by the Nutrition Labeling and Education Act of 1990.
Cross-sectional studies are those in which individuals are observed at only one point in time; such studies are
commonly known as surveys. The presence or absence of disease and the presence or absence of suspected
etiologic factors are determined in each member of the study population or in a representative sample at one
particular time. The advantages of cross-sectional studies are that they are relatively inexpensive to conduct,
and can be completed relatively quickly. However, cross-sectional studies reveal nothing about the temporal
sequence of exposure and disease, and necessarily use current exposure as a surrogate for past exposure.
Also, cross-sectional studies can only measure disease prevalence rather than incidence.
1. Descriptive Epidemiology Studies
a. Correlational Studies
b. Case Reports
2. Analytic Epidemiology Studies
a. Cross-Sectional Studies
b. Prospective Studies
Redbook 2000: VI.B Epidemiology
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In prospective studies, also called cohort or follow-up studies, the investigator selects a study population of
exposed and non-exposed individuals and follows both groups to determine the incidence of disease. The
group can be characterized by factors thought to influence the development or course of the disease and by
the presence or absence of risk factors (e.g., exposure or nonexposure to some agent). Prospective studies
generally imply study of a large population, study for a prolonged period of years, or both. This type of study
design is effective when there is good evidence of an association of the disease with a certain exposure (from
clinical observations or from descriptive epidemiology studies), when exposure is rare, but incidence of
disease among the exposed is high, and when the time between the exposure and disease is short. The major
advantage of prospective studies is that the incidence rates of the disease under study can be measured
directly; therefore, absolute and relative risks also can be measured directly. In addition, it is possible to
analyze the association of a particular exposure with several diseases, and a temporal relationship between
exposure and disease can be established.
There are a number of disadvantages to prospective studies, including: 1) The difficulty and expense of
conducting the studies, since both large study populations and long periods of observation are required for
definite results; 2) bias may be introduced if every member of the cohort is not followed; 3) the length of the
study may be less than the latency period of the disease; for example, if the study is stopped before old age,
many important diseases such as cancer may be missed; and, most importantly, 4) prospective studies are
very inefficient for studying rare diseases.
Results of prospective studies have been used at CFSAN in assessing the potential carcinogenic risk of some
compounds; for example, occupational cohort studies and studies of human populations accidentally exposed
to a carcinogen have been used in safety assessments of benzene, dioxin, and methylene chloride. FDA has
also provided financial support for prospective studies on accidental exposure to PBB's in a Michigan cohort,
and exposure to methylmercury in fish in a cohort of pregnant women (and their offspring) in the Seychelles
Islands.
In retrospective studies, also known as case-control studies, the investigator selects cases with a specific
disease, and appropriate controls without the disease, and obtains data regarding past exposure to possible
etiologic factors in both groups. The rates of exposure of the two groups are then compared. A case-control
approach is preferred when studying rare diseases, such as most cancers, because a very large number of
individuals would be needed in order to draw conclusions in a prospective study. Although it is possible to
detect the association of multiple exposures or factors with a particular disease, retrospective studies are
generally used to study diseases that have some unique and specific cause, such as infectious agents, in order
to avoid the problem of confounding etiologic factors.
Case-control studies can not determine directly absolute risk or relative risk because the incidence of disease
is not known in either the exposed or unexposed population as a whole. However, the relative risk can be
estimated in retrospective studies by the odds ratio, which is the ratio of the odds of exposure among cases
divided by the odds of exposure among controls. The odds ratio is a good approximation of the relative risk
when the subject cases are representative of all cases with regard to exposure, the controls are representative
of all controls with regard to exposure, and the disease being studied is rare.
Retrospective studies are much less expensive and less time consuming to conduct than are prospective
studies; usually, a relatively small population is needed for the study. Also, since the study selects only cases
of the disease of interest, there is no bias incurred in determining the endpoint. However, bias is frequently
incurred during detection and selection of cases, and during assessment of exposure. Controls should be
identical to the exposed cases except for the factor under investigation, a requirement which is often difficult
to achieve in practice. As with prospective studies, problems are frequently encountered in attempting to
control for competing risk factors and confounders. The investigators can adjust for known confounders either
by matching when selecting controls, statistically by stratification, or by use of regression models.
Results of case-control studies have been frequently used in safety evaluations at FDA, primarily to add
further information to the overall assessment of safety. In the past, FDA has supported case-control studies
on compounds of interest, such as the National Bladder Cancer Study and the use of artificial sweeteners. In
addition, FDA often looks carefully at the results of case-control studies in the setting of outbreaks of food-
borne disease to identify the food vehicle that was most likely responsible for transmitting the infectious
agent. The results then can be used to help target specific food vehicles for microbiologic testing as a means
of recovering the pathogen from the implicated food.
c. Retrospective Studies
Redbook 2000: VI.B Epidemiology
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Meta-analysis has been defined as "the statistical analysis of a large collection of analysis results from
individual studies for the purpose of integrating the findings". (3) The results of a well-done meta-analysis may
be accepted as a way to present the results of disparate studies on a common scale; however, caution should
be exercised before attempting to reduce the results to a single value as this may lead to flawed conclusions.
(2)
Several publications in the peer-reviewed literature serve as guidelines for the appropriate conduct of meta-
analysis, (6) , (7) the principal components of which include:
z Identifying criteria for the inclusion and exclusion of studies and avoiding biases in this process;
z Deciding whether the characteristics of study subjects, their interventions, and outcomes in each study
are comparable;
z Using well-defined methods for extracting data from the studies;
z Expressing the results of multiple studies in a consistent fashion;
z Using appropriate statistical methods to assess the data.
Where FDA evaluates a meta-analysis, the Agency considers such an analysis primarily as supporting
evidence, rather than as primary evidence, that can confirm the validity of data concerning a hypothesis. The
Agency must carefully scrutinize each meta-analysis to assess the soundness of its design and the quality of
the data from individual studies to determine the significance of the data. Such scrutiny requires review of the
original studies used for the meta-analysis.
1. 	Anonymous (1981) Reviews and Commentary. Guidelines for documentation of epidemiologic studies. A
report by the Epidemiology Work Group of the Interagency Regulatory Liaison Group. Am. J. Epidemiol.
114(5):609-613 	(Return)
2. 	Bailar, J.C. (1997) The promise and problems of meta-analysis. New Eng. J. Med. 337:559-561
(Return)
3. 	Glass, G.V. (1976) Primary, secondary and meta-analysis of research. Educ. Res. 5:3-8 	(Return)
4. 	Henkel, J. (1998) MedWatch. FDA's 'heads up' on medical product safety. FDA Consumer 32(6):10-
12,15 	(Return)
5. 	Last, J.M. eds. (1983) In, A Dictionary of Epidemiology. (J.H. Abramson, S. Greenland, M. C. Tuhriaus,
associate eds.: J. Amsel, assistant ed.) Oxford University Press, New York, N.Y 	(Return)
6. 	Sacks, H.S., Berrier, J., Reitman, D., Ancona-Berk, V.A., Chalmers, T.C. (1987) Meta-analyses of
randomized controlled trials. New Engl. J. Med. 316:450-455 	(Return)
7. 	Thacker, SB. (1988) Meta-analysis: a quantitative approach to research integration. JAMA 259:1685-
1689 (Return)
d. Meta-Analyses
3. Epidemiology Studies References
Redbook 2000: VI.B Epidemiology
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Safety/MedWatch/default.htm
Links on this page:
Redbook 2000: VI.B Epidemiology
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April 2004
Return to Redbook 2000 table of contents 1
This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It
does not create or confer any rights for or on any person and does not operate to bind FDA or the
public. You can use an alternative approach if the approach satisfies the requirements of the applicable
statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff
responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the
appropriate number listed on the title page of this guidance.
Redbook 2000: VII Glossary: Acronyms and Definitions
Toxicological Principles for the Safety Assessment of Food Ingredients
Redbook 2000
Chapter VII. Glossary: Acronyms and Definitions
Acronym 	Definition
Act 	"The Act", i.e., Federal Food, Drug, and Cosmetic Act
ABS 	chromosome aberration(s)
ADI 	acceptable daily intake
A/G 	albumin-to-globulin
ANOVA 	analysis of variance
B-cells 	B lymphocytes
B/T 	ratio of B to T lymphocytes
CAC 	Cancer Assessment Committee
CAS 	Chemical Abstract Service
CCFAC 	Codex Committee for Food Additives and Contaminants
CFR 	Code of Federal Regulations
CFSAN 	Center for Food Safety and Applied Nutrition
CHO 	Chinese hamster ovary [cell(s)]
CMI 	cell mediated immunity
CSO 	consumer safety officer
DNA 	deoxyribonucleic acid
DTH 	delayed type hypersensitivity
EAFUS 	Everything Added to Food in the United States (database)
ECVAM 	European Centre for the Validation of Alternative Methods
EDI 	estimated daily intake
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
Redbook 2000: VII Glossary: Acronyms and Definitions
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ELISA 	enzyme-linked immunosorbent assay
EPA 	Environmental Protection Agency (United States)
FAP 	food additive petition
FASEB 	Federation of American Societies for Experimental Biology
FASP 	food additive safety profile
FCS 	food contact substance
FCN 	Food Contact (Substance) Notification
FDA 	Food and Drug Administration
GLP 	good laboratory practices
GMPs 	good manufacturing practices
GRAS 	generally recognized as safe
HGPRT 	hypoxanthineguanine phosphoribosyl transferase activity
HTD 	highest treatment dose
IARC 	International Agency for Research on Cancer
ICH International Conference on Harmonisation of Technical Requirements for Registration of
Pharmaceuticals for Human Use
Ig 	immunoglobulin
JECFA 	Joint (FAO/WHO) Expert Committee on Food Additives
LOEL 	lowest observed effect level
LPS 	lipopolysaccharide
LSD 	least significant difference (refers to statistical test)
MFO 	mixed function oxidase
ML 	L5178Y mouse lymphoma cell
MLA 	mouse lymphoma assay
MLR 	mixed lymphocyte response
MTD 	maximum tolerated dose
OECD 	Organization for Economic Cooperation and Development
OFAS 	Office of Food Additive Safety (CFSAN)
PAFA 	Priority-Based Assessment of Food Additives (database)
PALS 	periarteriolar lymphocyte sheath
PB-PK 	physiologically based pharmacokinetic model
PHA 	phytohemagglutinin
PWM 	pokeweed mitogen
QAU 	Quality Assurance Unit
QRAC 	Quantitative Risk Assessment Committee
QRAs 	quantitative risk assessments
RBC 	red blood cells
Redbook I Toxicological Principles for the Safety Assessment of Direct Food Food Additives and Color
Additives Used in Food (1982)
Redbook II draft Toxicological Principles for the Safety Assessment of Direct Food Food Additives and Color
Additives Used in Food (1993)
Redbook 	Toxicological Principles for the Safety Assessment of Food Ingredients (2000, additions and
Redbook 2000: VII Glossary: Acronyms and Definitions
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2000 	updates in 2001, 2003, 2004)
RIA 	radio immunoassay
RNA 	ribonucleic acid
SAR 	structure activity relationship
SCE 	sister chromatid exchange
SHE 	Syrian hamster embryo cell
SOP 	standard operating procedure
SRBC 	sheep red blood cells
T-cells 	T-lymphocytes, or thymus derived cells
TK 	thymidine kinase
UDS 	unscheduled DNA synthesis
WBC 	white blood cells
WBA 	whole body autoradiography
Links on this page:
Redbook 2000: VII Glossary: Acronyms and Definitions
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000269

This draft guidance represents the Food and Drug Administration's (FDA's) current thinking on this
topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or
the public. You can use an alternative approach if such an approach satisfies the requirements of the
applicable statutes and regulations. If you want to discuss an alternative approach contact the FDA
staff responsible for implementing this guidance (Office of Food Additive Safety, 301-436-1200).
Draft Redbook II was distributed in 1993 by the Office of Premarket Approval. Effective June 18, 2001
the Office of Premarket Approval is now the Office of Food Additive Safety. Based on comments,
experience, and other information, FDA staff has revised and issued several sections of the draft as
final guidance in Redbook 2000 1 . Those sections of the 1993 Draft Redbook II not yet available in
Redbook 2000 are being placed here for your reference.
Section has been updated and finalized and can be found in Redbook 2000 2
(available in PDF 3 , 257KB)
A. 	Introduction
B. 	Expediting Review of Toxicology Information
C. 	Evaluating Toxicology Information
1. 	Introduction
2. 	No-Observed-Effect Level (NOEL)
3. 	Safety Factors
4. 	Acceptable Daily Intake (ADI)
5. 	Carcinogenic Risk Assessment
Section has been updated and finalized and can be found in Redbook 2000 4
1993 Draft Redbook II
Toxicological Principles for the Safety Assessment of
Direct Food Additives and Color Additives Used in Food
Redbook II
Draft Guidance
Table of Contents
Chapter I. Introduction
Chapter II. Agency Review of Toxicology Information in Petitions for Direct Food Additives and
Color Additives Used in Food
Chapter III. Recommended Toxicity Studies
Food
Home > Food > Guidance, Compliance & Regulatory Information > Guidance Documents
1993 Draft Redbook II
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A. 	Introduction
Section has been updated and finalized and can be found in Redbook 2000 5
B. 	General Recommendations for Toxicity Studies
1. 	General Guidelines for Toxicity Studies
Section has been updated and finalized and can be found in Redbook 2000 6 7
2. 	Summary Guidelines for Reporting the Results of Toxicity Studies
Section has been updated and finalized and can be found in Redbook 2000 8
3. 	Pathology Considerations in Toxicity Studies
Section has been updated and finalized and can be found in Redbook 2000 9
4. 	Statistical Considerations in Toxicity Studies
Section has been updated and finalized and can be found in Redbook 2000 10
5. 	Diets for Toxicity Studies (available in PDF 11
)
C. 	Guidelines for Recommended Toxicity Studies
1. 	Short-Term Tests for Genetic Toxicity
Section has been updated and finalized and can be found in Redbook 2000 12
2. 	Acute Oral Toxicity Tests (available in PDF 13 )
3. 	Short-Term Toxicity Tests with Rodents and Non-Rodents
Section has been updated and finalized and can be found in Redbook 2000 14
4. 	Subchronic Toxicity Tests with Rodents and Non-rodents
Section has been updated and finalized and can be found in Redbook 2000 15
5. 	Chronic Toxicity Studies
a. 	Chronic Toxicity Studies with Rodents
Section has been updated and finalized and can be found in Redbook 2000 16
b. 	One-Year Toxicity Tests with Non-Rodents
Section has been updated and finalized and can be found in Redbook 2000 17
6. 	Carcinogenicity Studies with Rodents
Section has been updated and finalized and can be found in Redbook 2000 18
7. 	Combined Chronic Toxicity/Carcinogenicity Studies with Rodents
Section has been updated and finalized and can be found in Redbook 2000 19
8. 	In Utero Exposure Phase for Addition to Carcinogenicity Studies with Reporting
Section has been updated and finalized and can be found in Redbook 2000 20
9. 	Reproduction and Developmental Toxicity Studies
Section has been updated and finalized and can be found in Redbook 2000 21
A. 	Introduction (available in PDF 22 )
B. 	Metabolism and Pharmacokinetic Studies (available in PDF 23 )
C. 	Neurotoxicity Studies
Section has been updated and finalized and moved to Redbook 2000 24 Chapter IVC10
D. 	Immunotoxicity Studies (available in PDF 25 )
Chapter IV. Guidelines for Toxicity Tests
Chapter V. Additional Recommended Studies
1993 Draft Redbook II
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1. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
2. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
A. 	Clinical Evaluation of Foods and Food Additives (available in PDF 26 )
B. 	Epidemiology Studies
Section has been updated and finalized and can be found in Redbook 2000 27
A. 	Introduction (available in PDF 28 )
B. 	Macro-Additives (available in PDF 29 )
C. 	Safety of Foods and Food Additives Developed by Biotechnology (available in PDF 30 , 428Kb)
D. 	Enzymes (available in PDF 31 )
E. 	Microbially Derived Food Ingredients (available in PDF 32 )
F. 	Advances in the Development of Alternatives to Whole Animal (Vertebrate) Testing (available in PDF 33 )
G. 	Heritable and Somatic Genetic Toxicity (available in PDF 34 )
Section has been updated and finalized and can be found in Redbook 2000 35
Chapter VI. Human Studies
Chapter VII. Emerging Issues in Safety Assessment of Food Additives and Color Additives Used
in Food
Chapter VIII. Glossary: Acronyms and Definitions
z 1993 Draft "Redbook II" Chapter II Agency Review of Toxicology Information in Petitions for Direct Food
Additives and Color Additives Used in Food (PDF - 86KB) 36
z 1993 Draft "Redbook II" Chapter IV B 5: Diets for Toxicity Studies (PDF - 73KB) 37
z 1993 Draft "Redbook II" Chapter IV C 2. Acute Oral Toxicity Tests (PDF - 62KB) 38
z 1993 Draft "Redbook II" Chapter V: Additional Recommended Studies Introduction (PDF - 30KB) 39
z 1993 Draft "Redbook II" Chapter V B. Metabolism and Pharmacokinetic Studies (PDF - 90KB) 40
z 1993 Draft "Redbook II" Chapter V D. Immunotoxicity Studies (PDF - 156KB) 41
z 1993 Draft "Redbook II" Chapter VI: Clinical Evaluation of Foods and Food Additives (PDF - 86KB) 42
z 1993 Draft "Redbook II" Chapter VII: Emerging Issues in Safety Assessment of Food Additives and Color
Additives Used in Food: Macro-Additives (PDF - 38KB) 43
z 1993 Draft "Redbook II" Chapter VII C: Safety of Foods and Food Additives Developed by
Biotechnology (PDF - 427KB) 44
z 1993 Draft "Redbook II" Chapter VII D: Enzymes (PDF - 28KB) 45
z 1993 Draft "Redbook II" Chapter VII E: Microbially Derived Food Ingredients (PDF - 19KB) 46
z 1993 Draft "Redbook II" Chapter VII F: Advances in the Development of Alternatives to Whole Animal
(Vertebrate) Testing (PDF - 67KB) 47
z 1993 Draft "Redbook II" Chapter VII G: Heritable and Somatic Genetic Toxicity (PDF - 51KB) 48
Links on this page:
1993 Draft Redbook II
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ntsandPackaging/Redbook/default.htm
3. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078724.pdf
4. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
5. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
6. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
7. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
8. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
9. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
10. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
11. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078728.pdf
12. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
13. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078734.pdf
14. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
15. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
16. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
17. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
18. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
19. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
20. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
21. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
22. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078736.pdf
23. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078741.pdf
24. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
1993 Draft Redbook II
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25. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078748.pdf
26. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078753.pdf
27. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
28. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078759.pdf
29. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078759.pdf
30. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078765.pdf
31. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078770.pdf
32. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078775.pdf
33. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078780.pdf
34. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078782.pdf
35. 	http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodIngredie
ntsandPackaging/Redbook/default.htm
36. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078724.pdf
37. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078728.pdf
38. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078734.pdf
39. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078736.pdf
40. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078741.pdf
41. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078748.pdf
42. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078753.pdf
43. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078759.pdf
44. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078765.pdf
45. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078770.pdf
46. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078775.pdf
47. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
1993 Draft Redbook II
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oodIngredientsandPackaging/Redbook/UCM078780.pdf
48. 	http://www.fda.gov/downloads/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/F
oodIngredientsandPackaging/Redbook/UCM078782.pdf
1993 Draft Redbook II
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Chapter VII
Emerging Issues in Safety Assessment
of Food Additives and Color Additives
Used in Food
A. Introduction
This section discusses approaches to testing that may be useful in assessing the safety of macro-additives
(see Cha pter V I B), bioengineered additives (see Cha pter V II C), additives that are enzymes (see Cha pter V II
D), and microbially-derived additives (see Cha pter V I E). This sectio n also disc usses the use of altern atives to
whole (vertebrate) animal testing in safety evaluation (see Cha pter V II F) and FDA's recognition of the potential
for direct food additives and color additives used in food to cause both heritable and somatic genetic toxicity (see
Cha pter V II G).
Because the Agency's approaches to determining the safety of these additives will continue to evolve for
some time, it is not yet appropriate to provide separate guidelines for acquiring toxicology information on the
types of additives in this document. In general, the Agency recommends that petitioners follow guidelines for
toxicity tests presented in other sections of this publication. In addition, this section suggests some im portant
issues to consider when planning a program of toxicity testing designed to demonstrate the safety of unique
additives. As always, we strongly recommend that petitioners discuss planned testing programs and protocols for
toxicity tests with Center scientists before tests begin.
B. Macro-Additives
Macro-additives are a class of food additives that are intended to be replacements for conventional
m acro-nutrie nts such as fats, proteins, and ca rbohyd rate s an d are intended for use at relativ ely high levels in food.
Mac ro-additives may be nutritive or non-nutritive; they may be reasonably pure, well characterized chemicals or
they may be com plex mixtures whose complete characterization is not feasible; they may be well absorbed from
the gastrointestinal tract or poorly absorbed; they may be m anufactured from unusual or novel food sources or
obtained by chem ical synthesis.
The comm on characteristic of macro-additives is that they will be consumed in large quantities compared
to conventional food additives and, as a consequence, they will present testing problems that require "customized"
approaches. For exam ple, it may not be feasible to calculate safety factors in the conventional w ay, that is, as a
fraction of the highest oral dose that has no adverse effects in animals. Other means of providing margins of
safety for macro-additives will have to be used; these may include information derived from m etabolic,
pharm acokinetic, and hum an clinical studies.
1. Nutritional Concerns in Animal Toxicological Tests
Be cause of the exp ected high leve l of hum an con sum ption of the se add itives, anim al test dose s that are
orders of m agnitud e greate r than the E xpec ted D aily Intake (ED I) for hum ans w ill often not be feasible. A ttem pts
to achieve very high doses in the animal studies might result in nutritional imbalances or caloric deprivation that
could c onfoun d interpreta tion of the tox icity studies. In orde r to test the high est dose feasible a nd yet a void
nutritional problems, it may be necessary for toxicity testing to be preceded by nutritional studies to determine
adequate test diets and appropriate con trol diets for animals in toxicity studies.
000276

If appropriate dietary controls include nutrient enhancement, care should be taken to avoid over-enriching
the diet or changing nutrient ratios that would mask toxicological endpoints under consideration. For example,
min eral oil as a te st ma terial wo uld be m ostly una bsorbed in the intestine whe re it wou ld solubilize fat-soluble
vitamins, leading to deficiencies of these nutrients. This effect may be eliminated by appropriate fortification of
the diet with vitamins A, D, E, and K. Quantities of nutrients to be used for fortifying the diet should be
determined experimentally, in relation to the amount of mineral oil (test substance) used. Under-fortification
could fail to protect against nutrient deficiencies and over-fortification could lead to altered toxicological
responses to xenobiotics and "background" pathology rates. Sufficiently great over-fortifications could produce
hypervitam inosis.
Control and test diets should be of the sam e caloric density and nutritionally (micronutrients) equal to test
diets. Selection of appropriate control diets may present particular problems when testing non-caloric food
substitutes o r food subs titutes that interfere with a bsorption o f nutrients. Du e to nutrien t variations in c how diets
from batch to batch , it is preferable to use a semi-purified diet base in these studies.
Additional information can be found in Chapter IV B 5, Diets for Toxicity Studies and in Chapter IV B
1, General G uidelines for Toxicity Studies.
2. Absorption, Metabolism, Distribution, and Elimination Studies
Studies designed to follow the metabolic path and fate of macro-additives take on particular importance
in providing assurance of safety if the conventionally calculated safety factor cannot be used. Greater
understanding of the disposition and pharmacokinetics of the additive should help to diminish uncertainties
regarding safety. Questions of the following types should be an swered through a ppropriate studies:
4 Does the product or its metabolites alter or interfere with absorption, metabolism, or excretion of
norma l nutrients or metabolic intermediates?
4 Does the produ ct or its metabolites alter the action of comm only used drugs?
4 Is the product absorbed, metabo lized, distributed, stored or excreted differently in man than in test
anima ls?
4 Does the product or its metabolites accumulate in tissues, and what are the toxicological consequences
if there is accumulation?
4 If the product is poorly absorbed, does the high concentration in the gut affect gut morphology,
physiology, or biochemistry? Are any changes in the gut morphology or biochemistry associated with the
deve lopm ent of neo plasm s of the gut?
4 Does the product alter the composition or nature of the gut flora? If it does, what are the toxicological
consequen ces of the changes?
3. Impurities and By-products
Because of the anticipated high human consumption levels of macro-additives, there is a concomitant
high potential intake of impurities and by-products. Therefore, every effort should be made to identify and
quantify the chemical constituents of the product. If any of these raise particular concerns, toxicity testing of the
impurity or by-product itself may be reco mm ended. Lim its for impu rities such as heavy m etals, natural toxins,
and an ti-nutrition factors m ay nee d to be sp ecified for the ma rketed p roduct.
4. Clinical Studies
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W hen animals studies have been completed or when there is reasonable assurance of safety of the macro-
additive from animal studies, clinical studies with human subjects may be useful for increasing confidence in the
safety of the product for human consumption. For example, humans may suffer subtle adverse effects not detected
in animal studies due to differences in physiology or metabolism between animals and humans; human
subpopulations (the old, young, and chronically ill) may each react differently to the food substitute. In addition,
hum an studie s m ay help com pensa te for the fact tha t conve ntional m ethods of calcu lating the A ccep table D aily
Inta ke (ADI) m ay not be a pplicable to the results of standard toxicity studies on m acro-a dditive s.
000278

VII D. Enzymes
Comm ercial enzyme products may be obtained from edible plants and animals and from non-toxigenic,
non-pathogenic microorganisms. Questions about the microbial source of the enzyme (see Cha pter V II E) and
the nature and level of enzyme preparation in the food are of concern in evaluating the safety of comm ercial
enzyme products because they influence the type and level of contaminating impurities in the food.
In general, enzyme preparations from organisms with a history of safe use do not require the same level
of toxicological testing as enzymes from sources without a history of safe use in food. The safety of comm ercial
enzym e products from sources w ithout a history of safe use in food usually is evaluated on a case-by-case basis,
but som e ge neraliz atio ns a bou t toxicology tests fo r these fo od a dditive s ca n be made.
Because of the protein nature of enzymes and their susceptibility to digestion when consumed, residues of
pure enzymes in processed food would be expected to have only limited toxic potential. If highly purified
preparations of microbial enzymes are used in food processing, exposure to the enzymes is usually reduced to the
parts-per-billion range. Such a level of exposure would ordinarily be too low to pose a safety concern, and
toxico logica l te sting may not be req uired. A n exc ep tio n to this gen eralization m ay occu r if review by the C en ter's
chemists results in concern for the presence in the enzyme preparation of a toxic material used in the purification
process; however, this is unlikely because of the requirement that food grade chemicals be used in purification.
In m ost c ase s, however, com m ercial e nzym e produ cts from micro bial sou rces are only pa rtially purified.
A variety of uncharacterized extraneous substances ("impurities") of biological origin may be present in the
enzy me prepara tion at leve ls com parable to the activ e ingred ient. The se substa nces h ave no technic al effect in
food proc essing, but a re allow ed to rem ain in the e nzym e produ cts bec ause the imp urities do no t interfere w ith
enzy me function. In ad dition, the en zym e prepa ration m ay con tain m ultiple enz ym e activities th at serve a variety
of useful fun ctions in pro cessing food. W hen the types an d levels o f impu rities in com me rcial enz ym e produ cts
from microbial sources are considered to be significant, the Agency ma y recomm end that safety be established by
appropriate toxicity testing. Such a requirement usually can be met by 90-day toxicity studies in the rat and the
dog. How ever, if review of the safety of the enzyme preparation raises questions about chem ical contam inants,
stability of the micro bial strain, produ ctio n of toxic products, etc., additional studies may be needed.
Enzym e products may be added directly to the food to be processed (e.g., rennet) or they may be
imm obilized on an ins oluble m atrix for use in p rocessin g liquid food s. Enzy me s are im mo bilized by secure
bonding (usually by m eans of a chem ical reaction) to an insoluble matrix. Liquid food products (e.g., corn syrup)
may be processed by passage over a column of the imm obilized enzyme. Only negligible amounts of the
imm obilized enzyme are expected to enter the processed food. Depending on the nature of the immobilization
matrix, however, some potential exists for contamination of the processed food by chemicals used in the
imm obilization process . If the Age ncy de cides tha t inform ation ab out the na ture of the fixing agent a nd its
potential migration to food raise questions of safety for foods processed by passage over an imm obilized microbial
enzyme, the Agency w ill recomm end that the imm obilized enzyme be subjected to 90-day toxicity studies in the
rat and the dog or other appropriate study.
As d escribed in the prec eding p aragrap hs, a variety o f factors w ill be taken into acc ount by the A genc y in
decidin g wh at inform ation is ne eded to assess th e safety o f additives th at are en zym es. Be fore con ducting toxicity
studies to assess the safety of such additives, petitioners should consult with Agency scientists. A com prehensive
review of the safety concerns relating to additives that are enzymes w ill be issued in a separate publication.
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VII E. Microbially Derived Food Ingredients
M icrobially d erived foo d ingredie nts m ay be fo od add itives (includ ing enz ym es), color add itives used in
foods and substitute foods. A unique concern about the safety of microbially derived food ingredients is the
microbial source; except for this concern, the safety of these ingredients will be evaluated as for analogues, non-
microbially derived ingredients. A variety of factors will be taken into account by the Agency in deciding what
inform ation is ne eded to assess th e safety o f mic robially de rived food ingredien ts. Before c onduc ting toxicity
stud ies to assess the sa fety of su ch ingredients, pe titioners should co nsu lt w ith A gency sc ientists. A
comprehensive review of the safety concerns relating to microbial sources will be issued in another publication.
000280

VII F. Advances in the Development of Alternatives to Whole
Animal (Vertebrate) Testing
Because anim al experimentation has become an em otional issue, it is important to recognize the growing
imp act of in vitro toxicology on the practic e of toxicology. A ltho ugh the field is often term ed "altern ativ e,"
expe rime ntal m odels ha ve bee n applie d to the three "R's" of R ussel an d B urch: 1 to replace anim al m odels, to
reduce the number of animals used, or to refine test methods to m inimize stress and suffering to anima ls.
This section is not intended as a guideline but serves to identify a future direction in methodology. In the
context of this document, "alternatives to whole animal (vertebrate) experimentation" refers to in vitro tests for
potential toxicity that substitute for or replace in vivo (whole an im al) studies. "In Vitro" literally means "in glass",
and is interpreted to mean "in a test tube" or "outside of the body".2 Alterna tive tests inclu de sho rt-term tests
using isolated cells, tissues, and organs and studies involving mathematical modeling, epidemiology, or the use of
human volunteers; short-term tests for genetic toxicity (see Chapter IV C 1) are exc luded.
In practice , alternative tes ts are used to suppo rt the plann ing and interpretation of wh ole anim al toxicity
studies and are not yet used as substitutes for toxicity studies using whole animals. For example, an alternative
test m ay be u sed 1) to de term ine the rela tive biolog ical pote ncy of a series of toxic ants at the cellular lev el, 2) to
select the animal model in which to conduct an in vivo test by comparing the metabolic properties of a toxicant at
the cellu lar level in se veral spe cies, and 3 ) to identify m echa nism (s) of toxicity by d efining the relationship
between exposure to a toxicant and development of various toxicological endpoints at the cellular, subcellular and
molecular levels of organization.
Recent advances that have been made in in vitro studies with isolated cells, tissues, and organs have
directed the scientific community toward developing, validating, and evaluating alternative test systems. The
predictive value of a standardized test must be assessed by means of a series of validation studies. Validation can
demonstrate that the use of an in vitro test is equivalent to the use of an established in vivo test or that the in vitro
test accurately predicts human toxicity. Anticipating a continued increase in the development and use of
alternative in vitro test system s, 3,4 the Agency encourages the development of approaches that can provide
information relevant to the assessm ent of huma n risks.
1. Reasons for Developing Alternative Tests
Several reasons to encourage the development of alternative in vitro tests are listed below:
4 Economy and efficiency: Once es tablished, in vitro tests m ay prov ide toxicity inform ation in a c ost-
e ffe ctiv e a nd tim e -sa vin g m a nn er. In fo rm a tio n g en era te d fro m in vitro test system s can b e used to
increase the efficien cy of w hole-an ima l studies an d decre ase the num ber of anim als used in toxicity
testing. Th e relative sim plicity and space -saving c haracte ristics of in vitro methods also are viewed as
advantages.
4 Information about hum an risk: Human cells, ethically obtained and successfully established in vitro,
m ay provide inform ation about a toxican t that is relev an t to hum an risk. F or exam ple, a toxica nt's
mechanism of action or metabolism in human cells can provide the basis for selecting a suitable animal
mod el for long-term toxicity studies.
2. Possible Applications of Alternative Tests
4 Isolated cells, tissues, and organs can be prepared and maintained in culture by methods that preserve
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properties characteristic of the same cells, tissues, and organs in vivo. Using such in vitro system s will
permit data to be generated under controlled experimental conditions and in the absence of many
com plicating fa ctors cha racteristic of ex perim ents w ith wh ole anim als. For exa mp le, the use o f cell
culture sy stem s will en able the me tabolism of a toxica nt that occ urs in one type of ce ll (i.e., hepatoc yte
cells) to be studied separately from a toxic endpoint that occurs in a different cell type.
4 Several toxic endpoints may lend themselves to quantification in an in vitro test system. Relevant
endpoints could be identified by comparing the action of a toxicant at cellular, subcellular or molecular
sites with the toxic effects observed in the target organ or tissue in vivo. Analysis of a broad spectrum of
in vitro cellular events may provide information about the in vivo progression of a toxic response as a
function of toxicant concentration and time.
4 Because in vitro proced ures hav e the po tential to yield reproduc ible m easure me nts, they theo retically
lend themselves to standardization. However, interpreting data obtained from a standardized in vitro
toxicity test with a reasonable degree of confidenc e can only occ ur after potential confounding factors,
such as interactions between the test agent and non-cellular components of the test system, have been
identified or elim inated. 5
4 The process of validation appears to be key to the full acceptance of alternative tests where the
reliability and relevance of procedures are established for specific purposes.6 While there is much
discussio n abou t the fram ew ork for this proc ess, severa l com pone nts appe ar essen tial to the ove rall
coordination of the validation process, including: scientific consensus on the definition of a validated
test, reference chem icals with defined toxicity and general ava ilability, a central repository for test
performance data and protocols, an established network of laboratories with the capabilities of method
valida tion , and scie ntific un derstanding o f the mechanistic basis of th e toxicological process involved.
An imp artial and c om petent g roup of scie ntists from regulatory agenc ies and th e resea rch com mu nity
could facilitate the implem entation of the validation process.
3. Limitations of Alternative Tests
Lim itations of in vitro tests are well known. For example:
4 In Vitro test system s are not a vailable for all tissues an d organ s. In addition, norm al system ic
mechanism s of absorption, penetration, distribution, and excretion are absent from in vitro test system s.
In Vitro systems lack the complex, interactive effects of the imm une, blood, endocrine systems, nervous
system , and other integrate d elem ents of the wh ole anim al. T hus , in vitro tests cannot be used to study
the complex nature of systemic toxicity.
4 Valid ation of ne w m ethods is time-c onsum ing and expen sive; acc eptanc e of in vitro tests as
alte rnative s to tradition al to xicity te sting in wh ole anim als is ex pected to be slow . 7 While many schemes
have been proposed to expedite these processes, no alternative in vitro test presently can replace an in
vivo toxicity study.
4. Current Use of In Vitro Tests
Numerous & diverse in vitro tests have been d evelop ed. The ir impo rtance a nd use have b een disc ussed in
any pu blic atio ns. 8-23 M any of the se tests w ill be im proved over tim e by the introduction of new scientific
information and technological advances in in vitro toxicology and related fields, such as molecular biology and
biotech nology . The A genc y enco urages the dev elopm ent and use of in vitro test systems for planning and
interpreting the results from w hole anim al toxicity studies.
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Significa nt adva nces h ave be en m ade in th e deve lopm ent of in vitro alternative s for ocular sa fety
testing.24-27 Othe r in vitro system s have been p roposed whic h m easure a broad range o f endpo ints and a re now in
various stages of validation. The Age ncy is currently part of an interagency regulatory groups evaluating these
proposed alternative test method s.
In Vitro approaches to toxicity testing can provide useful data when integrated with other information
abou t the toxicity o f food and color add itives used in food. R esults of in vitro tests can be used to optimize the
design of conv entiona l toxicity tests for a p articular test su bstanc e by he lping to de term ine app ropriate do se leve ls
and by helping to decid e w hich spe cies is the b est m odel for m an. Suc h im provem ents in the design o f who le
animal toxicity tests may reduce the number of test animals required to produce useful information about the
safety of proposed food and color additives used in food.
In Vitro tests can help elucidate the nature of the interaction between test substance and organism at the
cellular, subcellular, and molecular levels. Thus, once the critical target organ or organ system has been identified
in w hole an im al studies, in vitro tests ca n focus on the mechanism of actio n of the test substance at the target site.
Information from these studies can assist the Agency in making decisions about the safety of proposed food and
color additives used in food by comparing responses observed in human and animal cells and by facilitating
extrap olation from high-dose to low-dose re spo nse s.
At present, in evaluating a petition for the use of a food or color additive, the Ag ency considers in vitro
tests to be useful in helping to identify the mechanism(s) of action of the test substance and to provide information
about subtle effects observed in vitro that may not be observed in in vivo studies
References
1. Russell, W .M .S. and B urch, R .L., eds. (1 959 ) In, The principles of humane experimental technique.
M ethuen Press . Lo ndo n, U .K.
2. Schaeffer, W .I. (1990) Terminology associated with cell, tissue, and organ culture, molecular biology and
m olecular genetic s. In Vitro Cell Dev.Biol. 26:97-101.
3. Goldberg, A .M . and Fra zier, J.M . (198 9) A ltern ativ es to animals in toxicity te sting. Sc.Am. 261:24-30.
4. M cK eeha n, W .L., Barne s, D., Reid , L., Stanbridg e, E., Murakam i, H. and S ato, G. (199 0) Frontiers in
m am m alia n ce ll cu lture . In Vitro Cell Dev.Biol. 26:9-23.
5. Fra zier, J.M . and Bradlow , J.A., eds. (198 9) In, Technical problems associated with in vitro toxicity
te stin g sy ste m s. John's H opk ins U niversity P ress . Ba ltim ore, M D. Tech. Repo rt No.1.
6. Balls, M., Blaauboer, B., Brusick, D., Frazier, J., Lam b, D., Pemberton, M., Reinhardt, C., Roberfroid,
M., Rosenkranz, H., Schmid, B., Spielmann, H., Stamm ati, A. and W alum, E. (1990) Report and
recom m endation s for the CAAT/ER GATT W orksho p on the validation of toxicity te st procedures. ATLA
18:313-337.
7. Frazie r, J.M. (1990) S cientific criteria fo r validation of in vitro toxicity test. O rganiza tion for Ec onom ic
Co-O peratio n an d D evelopm ent. Environment Monograph No.36.
8. Atterw ill, C .K. a nd S teele, C .E., eds. (1 987 ) In, In Vitro methods in toxicology. Cam bridge U niversity
Pre ss. N ew Yo rk, N .Y.
9. Balls, M ., Ridde ll, R .J., and W orden, A.N . eds. (198 3) In, Anima ls and alternatives in toxicity testing.
Academ ic P ress . Ne w Yo rk, N .Y.
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10. Berky, J. and S herrod, C., e ds. (1 977 ) In, In Vitro testing 1975-1976. Franklin Institute Press.
Philad elphia, PA .
11. Bradlaw , J.A. (1986) Evaluation of drug and chem ical toxicity with cell culture systems.
Fund.Appl.Toxicol. 6:598-606.
12. Goldberg, A .M ., ed. (1 983 ) In, Product safety evaluation: Alternative methods in toxicology. Vol 1.
Liebert P ress . Ne w Yo rk, N .Y.
13. Goldberg, A .M ., ed. (1 984 ) In, Acute toxicity testing: Alternative methods in toxicology. Vol. 2. Lieb ert
Pre ss. N ew Yo rk, N .Y.
14. Goldberg, A .M ., ed. (1 985 ) In, In Vitro toxicolog y: Alte rnative m ethods in toxicolo gy. A p rogress rep ort
from the Johns Hopkins Center for Alternatives to Animal Testing. Vo l. 3. L iebert P ress . Ne w Yo rk, N .Y.
15. Goldberg, A .M ., ed. (1 987 ) In, In Vitro toxicolog y: Ap proach es to valid ation, A lternative m ethods in
toxicology. Vo l. 5. L iebert P ress . Ne w Yo rk, N .Y.
16. Grisha m, J.W . and Sm ith, G.J. (1984) P redictive a nd m echa nistic eva luation of tox ic respon ses in
m am m alia n ce ll cu lture system s. Pharmacol.Rev. 36:151s-171s.
17. Rofe, P.C . (197 1) T issu e cu lture and toxicology. Fd.Cosmet.Toxicol. 9:683-696.
18. Row an, A.N . and Stra tm ann, C .J., eds. (19 80) In, The use of alternatives in drug research. MacM illan &
Co. Press . Lo ndo n, U .K.
19. Rowan, A.N. and Goldberg, A.M. (1985) Perspectives on alternatives to current animal testing techniques
in preclinic al to xicology. Ann.Rev.Pharmacol.Toxicol. 25:225-247.
20. Stam ma ti, A.P., Silano, V., and Zucco , F. (1981) Toxicology investigations with cell culture systems.
Toxicol. 20:91-153.
21. Tard iff, R.G. (1978 ) In Vitro methods of toxicity e valuation . Ann.Rev.Pharmacol.Toxicol. 18:357-369.
22. Zucco, F. and Hooisman, J., eds. (1980) In, Proceedings of the international workshop on the application
of tissue culture in toxicology. Toxicol. 17:101-272.
23. Zu cco, F. and Ho oism an, J., eds. (19 82) In, Proceedings of the second international workshop on the
application of tissue culture in toxicology. Toxicol. 25:1-78.
24. Fra zier, J.M ., Ga d, S.C., Go ldberg, A.M . and M cC ulle y, J.P ., eds. (198 7) In, A critical evaluation of
alternatives to acute ocular irritation testing: Alternative methods in toxicology. Vol. 4. Liebert Press.
New York, N.Y.
25. Nardone, R.M. and Bradlaw, J.A. (1983) Toxicity testing with in vitro system s: I. O cular tissue cu lture . J.
Toxicol.-Cutaneous & Ocular Toxicol. 2:81-98.
26. Frazier, J.M. (1988) Update: A critical evaluation of alternatives to acute ocular irritancy testing. In,
Progress in In Vitro toxicology. (A. M . Go ldberg, ed.) L iebert P ress . Ne w Yo rk, N .Y. pp.67-75.
27. W ilcox, D .K. and B runer, L.H . (1990) In vitro alternatives for ocular safety testing: an outline of assays
and po ssib le future dev elopm ents. Altern. to Lab. Animals (ATLA) 18:117-128.
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VII G. Heritable and Somatic Genetic Toxicity
This chapter discusses FDA's interest in direct food additives and color additives used in foods that can
cause both he ritable and som atic gen etic toxicity . Wh ile the FD A c urrently ne ither recom me nds spe cific tests to
determ ine som atic and heritable g enetic to xicity, nor regu lates food and co lor additive s used in fo od on the basis
of such activities, the Agency has an heightened interest in this area.
1. Rationale for Testing for Heritable and Somatic Genetic Toxicity
He ritable gen etic toxicity is chem ically-indu ced da ma ge to the DN A of m ale and fem ale germ -line cells
that is not co rrectly repa ired, so that the d am aged gene(s) c an be in herited. Th e cons eque nces o f this genetic
toxicity ha s been we ll docum ented, an d a num ber of differen t genetic disease s have been c haracte rized. Som atic
genetic toxicity is chemica lly-induced dam age to the DN A of dividing and non -dividing somatic cells (i.e. non-
germ -line cells). Th e cons eque nce of so ma tic gene tic toxicity is tha t chem icals m ay alter ge ne func tions in
rapidly dividing somatic cells (e.g. intestinal lining and bone marrow) and in quiescent cells which may be forced
to replicate in response to a regenerative or mitogenic stim ulus (e.g. GoG1 periphe ral lym phoc ytes). Ge netic
dam age to these cells can lead to ca ncer and alteration of critical cellular functions (e.g. altered hormone and
recepto r site functions ).
2. Rationale for Selecting a Specific Test Battery
Currently the Agency recomm ends the use of a battery of genetic toxicity tests (see Chapter IV C 1 c)
for all chemicals that are direct food additives or color additives used in foods, including chemicals with structures
assigned to all three structure categories (see Chapter III B 2), as well as chemicals associated with Co ncern
Lev els I, II, and III (see Figure 4 in Chapter III B 1). These tests are rec om me nded to evalu ate the g enetic
toxicity of chemicals in order to identify those chemicals that may be direct acting carcinogens (see Chapter IV C
1).
Short-term tests for genetic toxicity can also be conducted to evaluate the effects of chemicals on the
genetic material of both somatic and germ-line cells, and the tests used for these purposes can overlap those used
for predicting carcinogenicity. For example, the data obtained from the Salmonella typhimurium reverse mutation
assay is not only useful in predicting the potential carcinogenicity of test substances,1,2,3 but it is also an important
means of determining whether a chemical has the potential to damage the genetic material in both germ-line and
somatic cells. Although FDA considers the information obtained from the test battery recomm ended in Chapter
IV C 1 to be useful in assessing a chemical's potential to cause heritable and somatic genetic toxicity, the
scientific community has not yet reached a consensus that these indicators are reasonably predictive of human
responses.
W hile FD A do es not rec om me nd a un ique ba ttery of tests for dete rmin ing heritab le and so ma tic gene tic
toxicity, the Agency recognizes that certain types of tests may be useful for this purpose.
Historically, gene mutations in germ line cells have been detected using in vivo tests such as the sex-
linked recessive lethal assay in Drosophila melanogaster and rodents. 4,5,6 Unfortunately, the
standard classical assay procedures are not completely satisfactory; each of these tests has one or more of the
follow ing lim itations:
4 standard procedures have a very low sensitivity for detecting known mutagenic chemicals, and the
assays fail to detect dose-related increases in chem ical activities;
4 standard protocols have m any deficiencies (e.g. they frequently lack concurrent positive controls,
m ultip le te st ch em ical doses are rare ly used , etc.);
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4 standard protocols fo r heritable ge netic toxic ity cann ot sim ultaneo usly m easure som atic cell tox icity in
the same animals; and
4 standard methods require large numbers of animals and are very time consuming and expensive.
Thu s, two grou ps of tests m ay prov ide a sen sitive m ethod for d etecting heritable a nd som atic cell ge netic
toxicity. First, a battery of tests for germ -line and so ma tic cell gen etic toxicity should inc lude the sam e short-term
genetic toxicity tests used to predict potential carcinogenicity {e.g. Salmonella typhimurium reverse mutation
assay, in vitro ML mutation assay and an in vivo cytogenetics assay (see Chapter IV C 1)}. Second, a battery of
tests for germ-line and somatic cell genetic toxicity also should include the use of transgenic mice. The Agency
recogn izes that c urrent gen etic toxicity tests using tran sgenic anim als do no t directly de mo nstrate he ritable gen etic
toxicity effec ts; how ever, che mic al-induc ed gen etic toxicity to germ cells dem onstrates th e poten tial for this to
occur. Since research with several different experimental rodent models has been progressing rapidly, and a
variety of tran sgenic rodents a re now com me rcially ava ilable, it ma y be po ssible in the fu ture to sim ultaneo usly
assess c hem ically-indu ced ge netic da ma ge to ge rm line cells and to a variety of som atic tissues. T he transg enic
test system should have several advantages over classical tests for heritable genetic toxicity:
# the investigator can easily manipulate the treatment conditions so that tissue-specific toxicological
effects can be com pared for different assay protocols;
# the test requires relatively few anim als (i.e. 2 or 3 animals per treatment group); and
# the test is relatively inexpensive an d can be perform ed in a m atter of days.
FDA continues to encourage the scientific comm unity to develop sensitive assays for detecting germ-line
and som atic cell genetic to xicity.
References
1. Te nna nt, R .W ., Margolin , B.H ., She lby, M .D., Z eiger, E ., Ha sem an, J.K., Spa ldin g, J., C asp ary, W .,
Re snick, M ., Stasiew icz, S., And erson, B . and M inor, R. (198 7) Predic tion of che mic al carcin ogen icity in
ro de nts fro m in vitro gen etic toxicity assays. Science 236:933-941.
2. Ashb y, J. and T ennant, R .W . (198 8) C hem ical structure, Salm one lla mutagenicity and extent of
carcinogenicity as indicators of genotoxic carcinogenesis among 222 chemicals tested in rodents by the
U.S. N CI/N TP . Mutation Research 204: 17-115.
3. Ash by, J. and T enna nt, R.W . (1991) D efinitive relation ships am ong ch em ical structure , carcinog enicity
and m utagenicity fo r 301 ch em icals tested by the U.S . NT P. Mutation Research 257: 229-306.
4. Abraham son, S., Wurgler, F.E., DeJongh, C. and Meyer, H.U. (1980) How many loci on the x-
chrom osom e of Drosophila melanogaster can mutate to recessive lethals? Environ.Mutagen. 2:447-453
5. Lee, W .R., Abraham son, S., Valencia, R., von Halle, E.S., W urgler, F.E. and Zimme ring, S. (1983) The
sex-linked recessive lethal test for mutagenesis in Drosophila melanogaster. A report of the U.S.
En viro nm ental P rote ctio n A gency G ene-T ox P rogram . Mutation Res. 123:183-279.
6. M ason, J.M ., Aaron, C .S., Lee, W .R., Sm ith, P.D., Tha kar, A., V alenc ia, R., W oodruff, R .C., W urgler,
F.E. and Zimm ering, S. (1987) A guide for performing germ cell mutagenesis assays using Dro sophila
melanogaster. Mutation Res. 189:93-102.
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