Guidance for Industry 
Reproductive and 
Developmental Toxicities  
Integrating Study Results to 
Assess Concerns  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
 
September 2011 
Pharmacology and Toxicology 
 
   
Guidance for Industry 
Reproductive and 
Developmental Toxicities  
Integrating Study Results to 
Assess Concerns 
 
 
 
Additional copies are available from: 
 
Office of Communications, Division of Drug Information 
Center for Drug Evaluation and Research 
Food and Drug Administration 
10903 New Hampshire Ave., Bldg. 51, rm. 2201 
Silver Spring, MD  20993-0002 
Tel: 301-796-3400; Fax: 301-847-8714; E-mail: druginfo@fda.hhs.gov 
http://www.fda.gov/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/default.htm 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
 
September 2011 
Pharmacology and Toxicology 
 
   
TABLE OF CONTENTS 
 
I.  INTRODUCTION.............................................................................................................1 
II.  BACKGROUND...............................................................................................................2 
A.  Data Needed for Integration and Assessment.............................................................................2 
B.  Types of Reproductive and Developmental Toxicity Evaluated................................................3 
1. Reproductive Toxicities....................................................................................................................3 
2. Developmental Toxicities.................................................................................................................4 
III.  THE INTEGRATION AND ASSESSMENT PROCESS..............................................5 
A.  Overall Decision Tree (Figure A).................................................................................................5 
1. Availability of Studies......................................................................................................................6 
2. Relevance of Studies........................................................................................................................6 
3. Presence or Absence of a Signal......................................................................................................6 
B.  No Signal (Figure B)......................................................................................................................7 
1. The Model/Test Species Predictive Adequacy.................................................................................7 
2. Adequacy of Study Doses and Exposure..........................................................................................8 
3. Class Alert........................................................................................................................................8 
4. Signals for Related Types of Reproductive and Developmental Toxicity........................................8 
C.  Reproductive or Developmental Toxicity Endpoints with Positive Signal (Figure C)............9 
1. Overview of Integration...................................................................................................................9 
2. Factors...........................................................................................................................................10 
3. Summary/Integration of Positive Findings....................................................................................14 
GLOSSARY.................................................................................................................................16 
FIGURES.....................................................................................................................................18 
 
 
  Contains Nonbinding Recommendations 
1
Guidance for Industry  
Reproductive and Developmental Toxicities  Integrating Study 
Results to Assess Concerns 
 
 
 
 
This guidance represents the Food and Drug Administrations (FDAs) 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 
 
This guidance describes an approach to estimating possible human developmental or 
reproductive risks associated with drug or biological product exposure when a nonclinical 
finding of toxicity has been identified, but definitive human data are unavailable.  The guidance 
is intended for applicants of new drug applications (NDAs) and biologics licensing applications 
(BLAs).  The recommendations included here will also help to ensure a consistent review of 
reproductive and developmental toxicity data among Center for Drug Evaluation and Research 
(CDER) review staff.  
 
This guidance does not (1) give detailed advice about labeling or placement of toxicity 
information in product labeling (for information on labeling, see 21 CFR 201.57); or (2) discuss 
clinical data or the integration of nonclinical and clinical data.  
 
FDA guidance documents, including this one, do not establish legally enforceable 
responsibilities.  Instead, guidances describe the Agencys 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.  
 
 
                                                 
1 This guidance was developed in the Center for Drug Evaluation and Research at the Food and Drug 
Administration. 
1  Contains Nonbinding Recommendations 
II.  BACKGROUND  
 
The approach presented here for assessing nonclinical reproductive and developmental toxicity 
data involves the integration and careful consideration of a variety of different types of 
nonclinical information: reproductive toxicology; general toxicology; and toxicokinetic and 
pharmacokinetic information, including absorption, distribution, metabolism, and elimination 
data.  The approach is used when there is a toxicity finding and focuses on assessing the 
likelihood that a drug will increase the risk of adverse human developmental or reproductive 
outcomes. The approach includes noting when studies were not conducted or when they were not 
performed using relevant model systems or at appropriate dose ranges. 
 
The general principles described here (i.e., a comprehensive analysis of available data) will 
typically be relevant to both drug and biological products, although some factors may not apply 
to biological products, because data may not be available for all factors considered in this 
guidance (e.g., cross-species concordance, dose-response, metabolism, relative exposure (animal 
: human) of >25-fold). For some oncology products (e.g., cytotoxics), certain aspects of the 
guidance may not apply because patients may be dosed at the maximum tolerated dose (MTD). 
 
Note:  Available clinical information to evaluate a drugs potential to increase the risk of an 
adverse developmental or reproductive outcome in humans should be evaluated separately and, 
when definitive, can supersede any nonclinical findings.  
 
A.  Data Needed for Integration and Assessment  
 
When determining what nonclinical data will be needed for integration and assessment, it is 
important to first evaluate a complete set of the expected general toxicology, reproductive and 
developmental toxicology, and pharmacokinetic studies.2  The evaluation should include an 
assessment of the drugs ability to produce a positive finding in the relevant animal studies (e.g., 
whether doses used were high enough to induce toxicity of some kind).  The evaluation should 
also compare animal and human pharmacodynamic effects, animal and human metabolism and 
disposition, animal and human pharmacologic and toxic effects, and drug exposures in animal 
studies in relation to the highest proposed dose in humans. The type and extent of available 
toxicology data may vary, depending on the products biological actions, test systems available 
for studying the compound, and other factors. In some cases, the data will not include all 
desirable general toxicology, reproductive/developmental toxicology, and pharmacokinetic 
studies. Nevertheless, the product should be evaluated to the extent possible according to the 
scientific principles and considerations described in this document (see section III).  
 
                                                 
2 See the following International Conference on Harmonisation (ICH) guidances for industry: M3(R2) Nonclinical 
Safety Studies for the Conduct of Human Clinical Trials for Pharmaceuticals; S3A Toxicokinetics: The Assessment 
of Systemic Exposure in Toxicity Studies; S5(R2) Detection of Toxicity to Reproduction for Medicinal Products & 
Toxicity to Male Fertility; and S9 Nonclinical Evaluation for Anticancer Pharmaceuticals. 
2  Contains Nonbinding Recommendations 
B.  Types of Reproductive and Developmental Toxicity Evaluated  
 
Reproductive and developmental toxicity can be manifested as a change in one or more specific 
endpoints.  For the purposes of this document, there are two broad toxicity categories  
reproductive and developmental  and, within those categories, eight classes of effects are 
considered (see Glossary).   
 
Classes of reproductive toxicity include:  
 
  male fertility  
  female fertility  
  parturition  
  lactation.  
 
Classes of developmental toxicity include:  
 
  mortality  
  dysmorphogenesis (structural abnormalities)  
  alterations to growth  
  functional impairment.   
 
For a given drug, endpoints reflecting the full range of potential reproductive and developmental 
effects should ordinarily be assessed (for standard endpoints, see ICH S5(R2)).  A positive signal 
of reproductive or developmental toxicity, whether in valid reproductive/developmental or other 
relevant nonclinical studies, should be evaluated to estimate the likelihood of increased 
reproductive or developmental risk for humans.  
 
1.  Reproductive Toxicities 
 
Reproductive toxicity refers to structural and functional alterations that affect reproductive 
competence in sexually mature males and females. Reproductive toxicity includes effects on 
male fertility and female fertility, parturition, and lactation.  
 
  Male Fertility  
 
Male reproductive toxicity includes damage to the reproductive organs, alterations in endocrine 
regulation of gamete maturation and release, reduction in sperm count, alterations in sperm 
motility or morphology, aberrant mating behavior, altered ability to mate, alterations in 
endocrine function, or overall reduction in fertility.  
 
  Female Fertility 
 
Female reproductive toxicity includes damage to the reproductive organs, alterations in 
endocrine regulation of gamete maturation and release, aberrant mating behavior, altered ability 
to mate, or overall reduction in fertility. Diminished fertility in female animals is typically 
3  Contains Nonbinding Recommendations 
detected by reductions in the fertility index, the number of implantation sites, time to mating, or 
fecundity.  
 
  Parturition  
 
Toxicities affecting labor and delivery in animals include abnormal or difficult delivery 
(dystocia) and changes in the onset or duration of parturition. Changes in the duration of 
parturition are frequently reported as mean time elapsed per pup, or total duration of parturition.  
 
  Lactation  
 
Drugs may alter the process of lactation in the nursing mother (e.g., the quality or quantity of 
milk), or may alter maternal behavior towards the nursing offspring. 
 
2.  Developmental Toxicities 
 
Developmental toxicity refers to adverse effects on the developing organism that result from 
exposure prior to conception, during the prenatal period, or postnatally up to the time of sexual 
maturity.  The four major manifestations of developmental toxicity are:  
 
  mortality  
  dysmorphogenesis (structural abnormalities)  
  alterations to growth 
  functional impairment 
 
  Mortality 
 
Mortality resulting from developmental toxicity may occur at any time from early conception to 
post-weaning (e.g., embryo-fetal death is a subset of mortality resulting from developmental 
toxicity).  Thus, a positive signal may appear as: 
 
  pre- or peri-implantation loss  
  early or late resorption  
  abortion  
  stillbirth  
  neonatal death 
  peri-weaning loss 
 
  Dysmorphogenesis (Structural abnormalities)  
 
Dysmorphogenic effects are generally seen as malformations or variations of the skeleton or soft 
tissues of the offspring and are commonly referred to as structural abnormalities.  
 
4  Contains Nonbinding Recommendations 
  Alterations in Growth  
 
Alterations in growth are generally seen as growth retardation, although excessive growth or 
early maturation may also be considered alterations to growth. Body weight is the most common 
measurement for assessing growth rate. Crown-rump length and anogenital distance may also be 
measured.  Sometimes it is not clear if an effect is a direct structural alteration or an inhibition of 
growth. For example, reduced ossification could be either. A distinction must be made upon 
review of all relevant data.  
 
  Functional Impairment  
 
Functional toxicities could include any persistent alteration of normal physiologic or biochemical 
function, but typically only developmental neurobehavioral effects and reproductive function are 
measured.  Common assessments include:  
 
  locomotor activity  
  learning and memory  
  reflex development  
  time to sexual maturation  
  mating behavior  
  fertility   
 
 
III.  THE INTEGRATION AND ASSESSMENT PROCESS 
 
Recommendations for wording in labeling should be based on the results of the integration and 
assessment process. The specific considerations leading to a risk conclusion should be provided. 
This information may later be helpful in discussions between FDA reviewers and applicants.      
 
The complete data integration process is divided into three components as discussed below in 
Sections A through C and presented schematically in Figures A through C at the end of this 
document. Briefly, Figure A is applicable to all data sets, Figure B is applicable only to data sets 
without evidence of reproductive or developmental toxicity, and Figure C is applicable to data 
sets with positive indications of reproductive or developmental toxicity.  
 
A.  Overall Decision Tree (Figure A) 
 
The decision process outlined in Figure A should be used for any of the endpoints of 
reproductive or developmental toxicity discussed in Section II.B.  For a given drug, studies may 
have been conducted to evaluate potential effects on none, some, or all of the endpoints of 
reproductive and developmental toxicity.  Where studies are available for any of the different 
endpoints, the outcome may be one or more positive signals, or no positive signal.  It is 
recognized that, in practice, one study may address several endpoints of toxicity and a study may 
be considered adequate to evaluate all, some, or none of the endpoints of toxicity addressed. 
Figure A depicts the sequential decisions that should be made in evaluating the various situations 
5  Contains Nonbinding Recommendations 
that may be encountered and the next steps that should be taken when there are evaluable studies 
with positive or negative findings.  
 
1.  Availability of Studies  
 
In Figure A, the first question asked for each category or class of toxicity is: "Were studies 
performed to assess the risk of that type of toxicity in humans, and are the detailed study results 
available for comprehensive evaluation?"  If no studies were conducted, or detailed study results 
are unavailable for comprehensive evaluation, the NDA or BLA review or applicant submission 
should explain that studies to assess the risk of that type of toxicity were not done, or are 
otherwise unavailable. In such circumstances, risk to humans is considered unknown or not 
evaluable.   
 
Example of wording: The risk of human [reproductive or developmental toxicity] with 
[Drug X] is unknown. There are no or inadequate data to evaluate its potential to cause 
human [reproductive or developmental toxicity].  
 
If studies were conducted and are available for comprehensive evaluation, the assessment 
process should continue with question 2.  
 
2.  Relevance of Studies  
 
The next question asked for each category or class of toxicity is: "Do the studies provide 
information relevant to assessing the risk of that type of toxicity for the proposed human use?"   
If the studies were not relevant or were otherwise inappropriate (i.e., inappropriate test protocol, 
nonrelevant route of drug administration), the NDA or BLA review or applicant submission 
should explain whyandshould discuss all supporting information that bears on study relevance. 
   
For example, the studies might have been potentially relevant, but the study design or conduct 
may have resulted in insufficient information to be useful. If the study was not relevant, the risk 
to humans is considered unknown or not evaluable.  
 
Example of wording: Animal data are insufficient to assess the risk of human 
[reproductive or developmental toxicity] with [Drug X].  
 
If the studies conducted were relevant to evaluating the risk of the particular type of toxicity in 
humans, the risk integration process should continue with question 3. Note that the processes in 
Figures B and C (see end of document) are intended to be used only when studies are considered 
adequate to assess the specified risk. They should not be used to evaluate findings (positive or 
negative) derived from inadequate studies.  
 
3.  Presence or Absence of a Signal  
 
If relevant studies are available and the study conduct (including doses and exposure and route 
of administration) is appropriate for assessing the risk of toxicity in humans, the next question 
asked should be, Was there a positive signal (suggesting toxicity)? If no signal was seen, the 
evaluation process should continue per Section B (Figure B).  A positive signal is a biologically 
6  Contains Nonbinding Recommendations 
meaningful difference in dosed animals compared to concurrent or historical controls. If a 
positive signal was seen, the evaluation process should continue per Section C (Figure C).  
 
If multiple studies are available to assess a particular type of reproductive or developmental 
toxicity (e.g., multiple studies would be expected for the evaluation of effects on embryonic 
development  ICH stage C), the process in Figure B should be used only if the results of all 
studies relevant to a particular aspect of reproductive or developmental toxicity were negative 
for that type of toxicity.  
 
If any study (general toxicity, reproductive, or developmental toxicology study) had a positive 
signal for that aspect of reproductive or developmental toxicity, the process in Section C (Figure 
C) should be used. 
 
B.  No Signal (Figure B)  
 
When there is no positive signal for an endpoint of reproductive or developmental toxicity, the 
risk assessment should be a step-wise process leading to a discussion in the NDA or BLA review 
or applicant submission of the applicability of the non-finding to humans. A graphic 
representation of this process is presented in Figure B. 
 
The following four sets of questions should be considered during the evaluation of each type of 
reproductive or developmental toxicity for which there was no signal.  
 
1.  The Model/Test Species Predictive Adequacy  
 
To what extent are the models or test species used likely to be predictive of human response? 
The questions below bear on determining a models predictive adequacy.  Affirmative answers 
to these questions would make the findings in that test system more credible in terms of human 
relevance.  
 
Do the models or test species (or systems) demonstrate the intended pharmacodynamic effect(s) 
of the drug?  
 
Do the models/test species (or systems) demonstrate an overall toxicity profile that is consistent 
with the human toxicity profile?  
 
Do the models/test species (or systems) demonstrate pharmacokinetic (including ADME)  
profiles for the drug that are qualitatively similar to those in humans?  
 
Negative answers to these questions may suggest that the response of the test species is of little 
relevance to humans, and the BLA or NDA review or applicant submission should explain why 
the animal study or studies conducted with the drug may not be fully adequate to evaluate the 
risk for the particular type of toxicity in humans (i.e., why the test may have low predictive 
value). Even if the test system is determined to be of limited relevance based on the above 
considerations, the review or applicant submission should consider the remaining questions (24 
7  Contains Nonbinding Recommendations 
below) and describe any additional uncertainties associated with the nonclinical data and the 
relevance of the studies to humans.  
 
2.  Adequacy of Study Doses and Exposure  
 
The following elements should also be considered in assessing the relevance to humans of the 
drug doses and exposure in the test system:   
 
Were adequate doses (concentrations) of the drug administered to the test species or test systems 
(e.g., MTD or maximum feasible dose (MFD); see ICH-S5R2 Note 7 (3.1))? (This would usually 
not apply to biologics.) 
 
Were the drug exposures (based on AUC, C , or other appropriate systemic exposure metric) 
max
achieved in the test species or test systems adequate relative to those expected in humans at the 
maximum recommended human dose (generally some multiple of the human exposure but at 
least equivalent to it)?  A greater relative exposure adds to the credibility of a negative finding. 
 
If the answer to either of these questions is no, the review or applicant submission should state 
that the animal studies conducted may be inadequate to fully evaluate the risk for the particular 
type of toxicity reported to be negative and should explain in detail why they may be inadequate. 
Even if the study doses and exposure are considered inadequate, the evaluation should proceed 
to the remaining sections (34 below), and any additional uncertainties should be described in 
the evaluation.  
 
3.  Class Alert  
 
Is there a class alert? Class alerts should be based on adverse reproductive or developmental 
effects previously demonstrated in humans by closely related chemical entities or compounds 
with similar pharmacodynamic effects. If there is a class alert for the drug based on a related 
chemical structure of parent or metabolite or related pharmacologic effect, the class-specific 
information relevant to the type of toxicity reported to be negative should be included in the risk 
evaluation and discussion of the drug.  
 
4.  Signals for Related Types of Reproductive and Developmental Toxicity  
 
The next step in evaluating the significance of a no-signal finding for a particular type of 
reproductive or developmental toxicity is to consider whether or not there are findings for related 
reproductive and developmental toxicities. A positive signal for one endpoint of toxicity may 
suggest some risk in humans for other toxicities in the same category for which there were no 
findings in animals. This may be a consequence of limitations of studies or cross-species 
differences in expression of effects. 
 
The issue of related toxicities is most applicable to developmental toxicities. For example, if 
there is no signal for fetal mortality, but a positive signal for alterations to growth or 
dysmorphogenesis in one (or more) animal species, it may be inappropriate to conclude there is 
no risk of fetal mortality for humans. Related toxicities may also be pertinent for reproductive 
8  Contains Nonbinding Recommendations 
toxicities where a hormonal mechanism is identified that could impact multiple aspects of 
reproductive performance and is relevant to humans. If positive signals for related endpoints of 
toxicity were observed in the animal studies, the evaluation should state that there was no 
observed effect on the type of toxicity being assessed, but positive signals were seen for related 
toxicities. If there is no positive signal for any type of reproductive or developmental toxicity in 
adequate studies, the evaluation should state that there is no expected increase in risk for 
reproductive or developmental toxicity in humans, based on the results of animal studies. 
 
C.  Reproductive or Developmental Toxicity Endpoints with Positive Signal (Figure C) 
 
1.  Overview of Integration 
 
A positive nonclinical signal for any type of reproductive or developmental toxicity should be 
analyzed with respect to various factors that may affect the level of concern for adverse effects in 
humans.  Since multiple factors contribute to the overall evaluation and conclusion, scientific 
judgment should be used to integrate all of the factors applicable to positive findings.   
 
These factors, discussed in greater detail below, include the following.  
 
  Cross-species concordance of reproductive or developmental effects 
  Multiplicity of effects 
  Maternal/paternal toxicity   
  Doseresponse relationship 
  Rare events  
  Pharmacodynamics: similarity between pharmacologic and toxicologic mechanisms  
  Concordance between test species and humans: metabolic and general toxicity profiles  
  Relative exposure  
  Class alerts 
 
These and other factors can either increase or decrease the level of concern. Examples of factors 
increasing concern when associated with a given positive signal include: low relative exposure in 
animals, presence of cross-species concordance, absence of maternal toxicity, and similarity 
between pharmacologic and reproductive/developmental toxicologic mechanisms. Conversely, 
concern may be decreased by: high relative exposure in animals, absence of cross-species 
concordance, excessive maternal toxicity, and animal-specific mechanisms. Case by case, some 
factors, such as relative exposure, can have a greater impact than others.  Some of the factors 
may not apply to biologics or to products for oncology indications because the relevant data 
(e.g., from multiple species) may not exist or be expected (see ICH S6(R1)).  The review or 
applicant submission should discuss the various factors and describe how the overall conclusion 
was reached. 
 
The implicit assumption of the integrative assessment shown in Figure C is that the process 
begins with a positive signal that is evident in one or more of the examined species (either in a 
reproductive or developmental toxicology study or an effect on a reproductive 
tissue/system/behavior in a general toxicology study). 
 
9  Contains Nonbinding Recommendations 
Note: Human data are considered separately from nonclinical findings, and human data may 
dramatically influence the overall assessment of human risk of reproductive or developmental 
toxicity, since definitive human data would supersede any nonclinical data.  
 
2.  Factors 
 
  Cross-species concordance of reproductive or developmental effects 
 
The observation of positive signals for the same or a related type of toxicity in more than one 
species is described as cross-species or interspecies concordance.  In general, findings for which 
there is cross-species concordance are more convincing than findings in a single species; thus, 
there is increased concern for reproductive or developmental toxicity in humans when cross-
species concordance of these effects is observed in nonclinical studies.  In evaluating potential 
human risk for adverse reproductive or developmental outcomes, if there is cross-species 
concordance for a single type of adverse effect it may be reasonable to conclude that a similar 
effect is the most likely adverse event to be seen in humans treated with the drug.  However, 
cross-species concordance is not limited to the observation of the same specific effect across 
species.  If different but related adverse effects are seen in multiple test species (e.g., alterations 
to growth in one species and developmental mortality in another, or parturition effects in one 
species and lactation effects in the second), it is assumed that there is an increased level of risk 
for categorically related endpoints in humans.  
 
Cross-species concordance is most likely to be identified for developmental endpoints examined 
in the organogenesis testing paradigm, in which multiple species are typically evaluated. 
However, alterations to endocrine function or gonadal histopathology (which may alter fertility) 
may be indirectly detected in subchronic and chronic toxicity studies in rodents and nonrodents. 
For alterations to parturition or lactation, it is often not possible to assess cross-species 
concordance because pre- and postnatal studies to assess these toxicity classes are usually done 
in only a single species. Although there may be less concern when a signal is detected in only 
one species, it is important to determine whether the negative species is an appropriate animal 
model and the studies were adequate in design, dosing, and implementation. 
 
  Multiplicity of effects 
 
Multiplicity of effects refers to the observation, in a single species or animal model, of two or 
more positive signals within one of the two general categories of toxicity (reproductive or 
developmental) or within one of the classes of reproductive or developmental toxicity. Evidence 
of multiple effects in an animal species is associated with increased concern for reproductive or 
developmental toxicity in humans, while an isolated finding is generally of less concern. The 
observation of positive signals in multiple classes of reproductive or developmental toxicity 
(e.g., increased malformation and embryo-fetal death) or of multiple signals for the same class of 
effects (e.g., motor and cognitive functional deficits) can represent intraspecies concordance or 
reflect signal strength by demonstrating effects in more than one setting or on more than one 
reproductive or developmental process. For example, developmental mortality can be manifested 
as early or late resorption, abortion, or stillbirth. If a positive signal in animals is observed at 
different stages of development, there is generally greater concern for adverse human 
10  Contains Nonbinding Recommendations 
reproductive outcomes than if a positive signal is observed only during a single, discrete period. 
If the positive signal occurs only for processes that are of limited relevance to humans, there 
would be less concern for adverse human outcomes. In addition to its relevance to this evaluation 
process, it is also important to define the timing of the period of susceptibility for the observed 
positive signal to provide a context for the human risk.  
 
  Maternal/paternal toxicity  
 
In weighing a signal of toxicity, the relationship of adverse reproductive or developmental 
effects to maternal (and, for fertility studies, paternal) toxicity should be considered when 
assessing the level of concern.  This assessment is relevant to all endpoints of reproductive and 
developmental toxicity.  A positive signal occurring at doses that are not maternally toxic 
increases concern for human reproductive or developmental toxicity.  If a positive signal is 
observed only in the presence of frank maternal toxicity, there may be decreased concern, 
provided that the positive signal can reasonably be attributed to maternal toxicity (i.e., a causal 
relationship between parental toxicity and the signal is established or biologically plausible,3 and 
the observed parental toxicity is not expected in humans).  When evaluating a positive signal in 
two or more species, assessment of the implications of maternal or paternal toxicity should be 
based on a composite analysis of the data from all adequately studied species.  If any species is 
considered inappropriate for assessing the implications of maternal or paternal toxicity, the 
evaluation should be performed using the remaining available data.  
 
  Dose-response relationship  
 
Concern for human reproductive or developmental toxicity increases when a positive signal is 
characterized by any of the following: (1) increased severity of adverse effects with an increase 
in dose, (2) increased incidence of adverse effects with an increase in dose, or (3) a high 
incidence of adverse effects across all dosed groups. Conversely, there is generally less (or 
decreased) concern when these indices of dose-response are absent.  
 
  Rare events  
 
Developmental toxicity studies usually lack the statistical power to detect subtle increases in rare 
events. Thus, an increased frequency of rare events in drug-exposed animals increases concern 
for reproductive or developmental toxicity in humans. The absence of an increased frequency of 
rare events, however, does not decrease concern.  
 
  Pharmacodynamics: similarity between pharmacologic and toxicologic mechanisms 
 
For drugs with a positive signal, the similarity between the pharmacologic and reproductive or 
developmental toxicologic modes of action should be assessed, to the extent that these are 
understood. If a positive signal is an extension or progression of, or related response to the drug's 
intended pharmacologic mode of action (e.g., delay of parturition by drugs known to suppress 
                                                 
3 The attribution of adverse effects to maternal (or paternal) toxicity can be based on previously collected data 
demonstrating the relationship between the maternal/paternal and reproductive or developmental effects. 
11  Contains Nonbinding Recommendations 
uterine smooth muscle contractility or hypotension in the offspring of dams treated during late 
gestation with a drug known to lower blood pressure), there is increased concern for 
reproductive or developmental toxicity in humans. There generally is less (or decreased) concern 
if the positive signal is attributed to an animal-specific pharmacological response, even though it 
may be an extension of the drug's pharmacologic effect (e.g., pregnancy loss in rats due to hypo-
prolactinemia).  
 
  Concordance between test species and humans: metabolic and general toxicity profiles 
 
The concordance between the metabolic and drug distribution profiles and general toxicity 
profiles in the test species and humans should be evaluated for drugs with a positive signal.  
 
  Metabolic and drug distribution profiles   
 
Drug distribution, elimination, and biotransformation (pathways and metabolites) in the 
test species and in humans should be compared. Quantitative differences in 
metabolic/drug distribution profiles between the test species and humans are often seen, 
may not have important implications, and should not be overemphasized.  Reproductive 
and developmental toxicities in animals induced by compounds whose metabolic and 
distribution profiles are very similar in animals and humans increases concern for 
reproductive or developmental toxicity in humans.  
 
For compounds with highly dissimilar metabolic or tissue distribution profiles in animals 
and humans, there is generally less concern if the toxic effect seen in the test species can 
reasonably be attributed to a metabolite or tissue distribution profile not seen in humans. 
However, when there are significant differences in drug distribution or metabolic profiles 
between several species, yet each test species demonstrates a positive signal for a 
reproductive or developmental toxicity, the toxicity is assumed to be attributable to the 
parent drug or a common bio-transformed product and concern is increased.  
 
  General toxicity profiles  
 
If a drug's overall toxicity profile in one or more test species with a positive signal is 
similar to that in humans, there is increased concern for reproductive or developmental 
toxicity in humans. If the overall toxicity profiles are dissimilar, there is generally less 
(or decreased) concern. When general toxicology data are available for more than one 
species, the determination of the level of concern should be based on an assessment of 
each test species ability to predict human adverse effects in response to the drug.  
 
  Relative exposures  
 
When considering the relative exposure comparisons discussed below, more emphasis should be 
placed on a parameter within this factor when there is a scientifically plausible link between the 
exposure metric and the adverse reproductive or developmental effect. For example, when a 
correlation between peak plasma concentration and a developmental effect has been 
12  Contains Nonbinding Recommendations 
demonstrated for a particular drug, Cmax would be considered the most relevant exposure metric 
for making animal to human comparisons for that endpoint.  
 
  Kinetic comparison of relative exposure  
 
Comparison of systemic drug exposure at the No Observed Effect Level (NOEL) for the 
reproductive or developmental toxicity in the test species to that in humans at the 
maximum recommended dose is a critical determination. This comparison should be 
based on the most relevant metric (e.g., AUC, Cmax, Cmin, body surface area-adjusted 
dose). In general, there is increased concern for reproductive or developmental toxicity in 
humans for relative exposure ratios (animal: human) that are <10 and decreased concern 
for exposure ratios >25. When applicable, the relative exposure ratio should consider 
both the parent compound and its metabolites. For example, it is appropriate to combine 
parent and metabolite when both are pharmacologically active and the activity is known 
to relate to the reproductive or developmental toxicity. When there are exposure data for 
multiple test species, the NOEL exposure for each should be compared to human 
exposure at the maximum recommended dose. If the exposure ratios are low (<10 fold) in 
multiple species with a positive signal, there is increased concern. If the exposure ratios 
are high (>25 fold), there is generally less (or decreased) concern. In the event that a 
significant difference in relative exposures is observed between multiple test species, the 
appropriateness of the metric (for example, AUC, Cmax) being used to define the 
interspecies exposure comparisons should be reassessed. If an alternative metric fails to 
reduce the disparity between species, the assessment of concern should be based on the 
lowest ratio (i.e., in the most sensitive species).  
 
Relative interspecies exposure data should be evaluated in light of possible species 
differences in protein binding (free drug concentration), receptor affinity (if related to the 
positive signal) or site-specific drug concentrations. In the absence of meaningful 
differences between the test species and humans in these parameters, the interspecies 
comparisons should be based on total drug exposure.  
 
  Biomarkers as a measure of relative exposure  
 
The purpose of this relative exposure metric is to compare the dose causing reproductive 
or developmental toxicity in the test species to the therapeutic dose in humans, 
normalized to the doses causing a response common to both species. In practice, this is 
done by taking the exposure at the NOEL for the adverse reproductive or developmental 
effect and dividing by the exposure at which the biomarker response is seen in the test 
species. This is compared to the human therapeutic exposure divided by the exposure at 
which the biomarker response is seen in the human. The ratio calculated for animals is 
then divided by the ratio calculated for humans. When this ratio of relative biomarker 
exposure (animal: human) is < 10, there is generally increased concern for human 
reproductive or developmental toxicity. When this ratio is > 25, there is generally less 
concern.  
 
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When there are data to compute relative biomarker exposure ratios for multiple species, 
the level of concern assessment should be based on an integrated analysis of data from all 
adequately studied species. When there are non-concordant biomarker ratios between 
multiple test species, the relevance of the biomarker as expressed in the various species 
should be considered before making an assessment. If there is no scientific rationale for 
the disparity between species, the biomarker, as a measure of exposure, will be of 
questionable utility.  
 
  Class Alerts  
 
Consideration of a class associated effect should be based on prior human experience for a drug 
with closely related chemical structure (parent or metabolite) or related pharmacologic effect and 
with known reproductive or developmental outcomes in humans. There is increased concern for 
reproductive or developmental toxicity in humans when the drug is from a class of compounds 
known to produce adverse effects in humans and animals. There is decreased concern only in 
circumstances in which a class of compounds, although demonstrating adverse effects in 
animals, has previously been shown definitively to have no related adverse effects on human 
reproduction or development.  
 
3.  Summary/Integration of Positive Findings 
 
When there is a positive finding in nonclinical studies for one or more endpoints of reproductive 
or developmental toxicity, there is a potential for increased human risk. Multiple considerations 
contribute to the overall evaluation of the nonclinical data and conclusions regarding human risk. 
These include factors that can modify the level of concern for human adverse effects determined 
from the nonclinical signal. Factors can increase or decrease concern, and some factors can carry 
greater weight than others. Positive signals should be evaluated to estimate the likelihood of 
increased reproductive or developmental risk for humans using the following general procedure:  
 
  In evaluating the level of increased risk, all relevant information should be considered, 
including nonclinical reproductive and general toxicology data and human and animal 
pharmacodynamic and pharmacokinetic data.  
 
  Factors that may affect the level of concern associated with a positive signal of 
reproductive or developmental toxicity should be assessed. 
 
  The analysis should take into account the quality and type of data under consideration. 
 
  A weight of evidence approach should then be applied to arrive at an overall conclusion 
for reproductive or developmental toxicity (Figure C). The following are examples of 
possible summary risk conclusions for the evaluation:  
 
  Does Not Appear to Increase Risk: The drug is not anticipated to increase the risk 
of adverse developmental (or reproductive) outcomes in humans when used in 
accordance with dosing information in the product label. 
 
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  May Increase Risk: The drug may increase the risk of adverse developmental (or 
reproductive) outcomes in humans when used in accordance with the dosing 
information in the product label.  
 
  Predicted to Increase Risk: The drug is expected to increase the risk of adverse 
developmental (or reproductive) outcomes in humans when used in accordance 
with the dosing information in the product label. 
 
The factors discussed above are derived from a limited sample of pharmaceuticals for which the 
clinical outcomes are reasonably well defined and are not considered exhaustive. CDER believes 
that using the various factors to assess a drugs potential to increase the risk of adverse 
reproductive and developmental outcomes in humans will result in a more accurate as well as 
more unbiased and uniform evaluation. CDER also believes this approach will help identify 
specific areas in which additional information about a pharmaceutical would be useful in more 
fully defining risk and would enable specific analyses of areas of disagreement that influence the 
risk evaluation.   
 
 
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GLOSSARY 
 
ADME  bsorption, distribution, metabolism, and elimination  
 
Class Alert  A structurally adverse reproductive or developmental effect previously 
demonstrated in humans by related chemical entities or compounds with similar 
pharmacodynamic effects  
 
Developmental Toxicity  ny adverse effect induced prior to attainment of adult life. It 
includes effects induced or manifested in the embryonic or fetal period and those induced or 
manifested postnatally. These are divided into four major manifestations or classes: mortality, 
dysmorphogenesis, alterations to growth, and functional toxicities.  
 
Factor  For purposes of this guidance, a factor is one of the various considerations used to 
evaluate the level of concern for a positive signal of developmental or reproductive toxicity. The 
factors include (1) Cross-species concordance of reproductive or developmental effects; (2) 
Multiplicity of effects; (3) Maternal/paternal toxicity; (4) Doseresponse relationship; (5) Rare 
events; (6) Pharmacodynamics: similarity between pharmacologic and toxicologic mechanisms; 
(7) Concordance between test species and humans: metabolic and general toxicity profiles; (8) 
Relative exposure; and (9) Class alerts.  They are summarized in Figure C and are discussed in 
Section C. 
  
Fertility  Reproductive competence  
 
Lactation  he secretion of milk or the period of milk secretion  
 
Malformation   permanent alteration (abnormality) in which there is a morphologic defect of 
an organ or a larger region of the body, resulting from an abnormal developmental process. They 
generally occur at a low frequency in the control population and/or will adversely affect survival, 
growth, or development of functional competence  
 
Maternal (Paternal) Toxicity  Toxicity to the mother (maternal) or the father (paternal) in a 
reproductive toxicology study, but not necessarily a toxicity to reproductive function  
 
Parturition  Labor and delivery  
 
Positive Signal   treatment-related reproductive or developmental toxicity  
 
Rare Event  An endpoint that occurs in less than 1 percent of the control animals in a study 
and in historical control animals  
 
Reproductive Toxicity  Structural and/or functional alterations that may affect reproductive 
competence in sexually mature males and females. These may be manifested as impairment of 
fertility, parturition, or lactation.  
 
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Structural abnormalities  Includes malformations and variations 
 
Toxicologic Effect  ny adverse effect of a therapeutic agent 
 
Variation  An alteration that may occur at a relatively high frequency and/or represents a 
retardation in development, a transitory alteration, or a permanent alteration not believed to 
adversely affect survival, growth, development, or functional competence 
 
17  Contains Nonbinding Recommendations 
FIGURES 
 
 
 
18  Contains Nonbinding Recommendations 
19  Contains Nonbinding Recommendations 
 
 
20