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 Industry1

Reproductive and Developmental Toxicities — Integrating Study 

Results to Assess Concerns

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 

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 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. 

 

1

 This guidance was developed in the Center for Drug Evaluation and Research at the Food and Drug 

Administration. 
Contains Nonbinding Recommendations 

2 

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 drug’s 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 drug’s 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 product’s 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. 
Contains Nonbinding Recommendations 

3 

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 
Contains Nonbinding Recommendations 

4 

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. 
Contains Nonbinding Recommendations 

5 

• 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 
Contains Nonbinding Recommendations 

6 

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 why and should 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 
Contains Nonbinding Recommendations 

7 

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 model’s 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 (2–4 
Contains Nonbinding Recommendations 

8 

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, Cmax, or other appropriate systemic exposure metric) 

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 (3–4 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 
Contains Nonbinding Recommendations 

9 

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 

– Dose–response 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). 
Contains Nonbinding Recommendations 

10 

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 crossspecies 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 
Contains Nonbinding Recommendations 

11 

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. 
Contains Nonbinding Recommendations 

12 

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 hypoprolactinemia). 

• 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 
Contains Nonbinding Recommendations 

13 

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. 
Contains Nonbinding Recommendations 

14 

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. 
Contains Nonbinding Recommendations 

15 

– 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 drug’s 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. 
Contains Nonbinding Recommendations 

16 

GLOSSARY

ADME − Αbsorption, 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 − Αny 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) Dose–response 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 − Τhe secretion of milk or the period of milk secretion 

Malformation − Α 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 − Α 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. 
Contains Nonbinding Recommendations 

17 

Structural abnormalities – Includes malformations and variations 

Toxicologic Effect − Αny 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 
Contains Nonbinding Recommendations 

18 

FIGURES 
Contains Nonbinding Recommendations 

19 
Contains Nonbinding Recommendations 

20