Guidance for Industry 
 
Nonclinical Safety Evaluation 
of Drug or Biologic 
Combinations 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
 
March 2006  
Pharmacology and Toxicology 
   
Guidance for Industry 
 
Nonclinical Safety Evaluation 
of Drug or Biologic 
Combinations 
 
 
 
 
 
 
Additional copies are available from: 
 
Office of Training and Communications 
Division of Drug Information, HFD-240 
Center for Drug Evaluation and Research 
Food and Drug Administration 
5600 Fishers Lane 
Rockville, MD  20857 
(Tel) 301-827-4573 
http://www.fda.gov/cder/guidance/index.htm 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
 
March 2006 
Pharmacology and Toxicology 
 
   
TABLE OF CONTENTS 
 
I.  INTRODUCTION.............................................................................................................1 
II.  NONCLINICAL STUDIES FOR A COMBINATION OF TWO OR MORE 
PREVIOUSLY MARKETED DRUGS OR BIOLOGICS (FIGURE A).....................2 
A.  Safety Considerations....................................................................................................................3 
B.  Nonclinical Study Recommendations/General Procedure.........................................................4 
III.  NONCLINICAL STUDIES FOR A COMBINATION OF DRUGS OR BIOLOGICS 
WHEN ONE OR MORE IS PREVIOUSLY MARKETED AND ONE IS A NEW 
MOLECULAR ENTITY (FIGURE B)...........................................................................6 
A.  General Toxicology Studies...........................................................................................................6 
B.  Reproductive and Developmental Toxicology.............................................................................6 
C.  Animal Models of Efficacy............................................................................................................7 
D.  Further Studies..............................................................................................................................7 
IV.  NONCLINICAL STUDIES FOR A COMBINATION OF TWO OR MORE 
DRUGS OR BIOLOGICS WHEN ALL ARE NEW MOLECULAR ENTITIES 
(FIGURE C)......................................................................................................................7 
A.  General Toxicology Studies...........................................................................................................7 
B.  Animal Models of Efficacy............................................................................................................8 
C.  Safety Pharmacology.....................................................................................................................8 
D.  PK/ADME and Toxicokinetics......................................................................................................8 
E.  Genetic Toxicology.........................................................................................................................9 
F.  Special Toxicology..........................................................................................................................9 
G.  Reproductive and Developmental Toxicology.............................................................................9 
H.  Further Studies..............................................................................................................................9 
I.  Carcinogenicity............................................................................................................................10 
APPENDIX:  RECOMMENDED GENERAL PROCEDURES............................................11 
Figure A:  Combinations of Previously Marketed Drugs or Biologics............................................11 
Figure B:  Combinations of Previously Marketed Drugs or Biologics with NMEs........................12 
Figure C:  Combinations of NMEs with NMEs.................................................................................13 
  Contains Nonbinding Recommendations 
1
Guidance for Industry
Nonclinical Safety Evaluation of  
Drug or Biologic Combinations 
 
 
 
 
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 provides recommendations on nonclinical approaches to support the clinical study 
and approval of fixed-dose combination products (FDCs), co-packaged products, and some 
adjunctive therapies.2  The intent of this guidance is to delineate general guiding principles.  To 
receive more detailed advice regarding a particular drug or biologic combination development 
program, sponsors should contact the appropriate review division before submitting an 
investigational new drug application (IND).  In addition, the Food and Drug Administration 
(FDA) is in the process of publishing more specific guidance for certain categories of drug 
combinations.3   
                                                 
1 This guidance has been prepared by the Pharmacology Toxicology Coordinating Committee in the Center for Drug 
Evaluation and Research (CDER) at the Food and Drug Administration.  
 
2 For the purposes of this guidance, a fixed-dose combination product (FDC) is one in which two or more separate 
drug components (active pharmaceutical ingredients) are combined in a single dosage form.  A co-packaged product 
consists of two or more separate drug products in their final dosage forms, packaged together with appropriate 
labeling to support the combination use.  An adjunctive therapy refers to the situation in which a patient is 
maintained on a second drug product that is used together with (i.e., in adjunct to) the primary treatment, although 
the relative doses are not fixed, and the drugs or biologics are not necessarily given at the same time.  Adjunctive 
therapy products may be co-packaged, and may or may not be labeled for concomitant use.  However, adjunctive 
therapies are only covered in this guidance when the adjunctive therapy products are already labeled for concomitant 
use, a sponsor intends to seek labeling to address concomitant use, or when, in light of the factors described in 
section II.A, there is an identified cause for concern about a potential serious interaction.  For the purposes of this 
guidance, the terms co-packaged product, FDC, and adjunctive therapy are collectively referred to as combinations.  
 
3 For example, the Agency is developing a draft guidance specifically addressing oncologic drug combinations.  In 
addition, in May 2004 (69 FR 28931), the Agency made available the draft guidance for industry Fixed Dose 
Combination and Co-Packaged Drug Products for Treatment of HIV (draft HIV guidance).  When finalized, this 
guidance will provide recommendations on FDCs and co-packaged versions of previously approved antiretroviral 
therapies for the treatment of human immunodeficiency virus (HIV).  Sponsors should consult these additional 
guidances when preparing an application for one of these types of products.  
  1 Contains Nonbinding Recommendations 
 
Drug and biologic combinations may involve: (1) two or more previously marketed drugs or 
biologics4 (MD/Bs); (2) one or more new molecular entities (NMEs) and one or more previously 
marketed drugs or biologics; or (3) more than one NME.  The nonclinical studies considered 
important for each type of combination may differ, depending upon the information available on 
each drug substance.  The nonclinical studies that the FDA recommends sponsors use to 
characterize the combination will depend on the toxicologic and pharmacokinetic profiles of the 
individual drugs or biologics, the treatment indication or indications, and the intended 
population.  The number and type of studies will depend on the stage of clinical development. 
 
In this guidance, each of the three general types of combinations (i.e., MD/B-MD/B, MD/B-
NME, and NME-NME) will be discussed separately.  This guidance covers combinations of 
drugs and biologics regulated by the Center for Drug Evaluation and Research (CDER).  The 
ICH guidance for industry S6 Preclinical Safety Evaluation of Biotechnology-Derived 
Pharmaceuticals should also be consulted for nonclinical development of biologic products.5  
 
FDAs guidance documents, including this guidance, 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. 
 
 
II.  NONCLINICAL STUDIES FOR A COMBINATION OF TWO OR MORE 
PREVIOUSLY MARKETED DRUGS OR BIOLOGICS (FIGURE A) 
 
This section addresses the situation in which a sponsor submits an application to develop a 
combination of two or more previously marketed drugs or biologics or a combination of drugs 
and biologics.  Generally the FDA believes that, in such a situation, sufficient clinical and 
nonclinical data will exist for each drug product separately.  However, the indications for which 
each drug is marketed should be compared to those for which the combination is being proposed.  
For example, drug products marketed for acute use may not have nonclinical data to support 
chronic use.  To the extent that there are gaps in the data, the FDA may recommend that 
additional nonclinical studies be conducted.6
                                                 
4 For purposes of this guidance, the phrase previously marketed drugs or biologics includes both drug/biologic 
products and active pharmaceutical ingredients. 
 
5 We update guidances periodically.  To make sure you have the most recent version of a guidance, check the CDER 
guidance Web page at http://www.fda.gov/cder/guidance/index.htm. 
 
6 In certain cases, adequate clinical data may exist not only for the individual components of a drug or biologic 
combination, but also for their concomitant use.  In such cases, additional nonclinical studies may not be necessary.  
For example, the draft HIV guidance referenced in Footnote 3 discusses the FDAs belief that certain antiretroviral 
therapies previously approved for the treatment of HIV may be approved for use in combination without additional 
in vitro studies, because the clinical safety and efficacy of concomitant use have been evaluated and described in 
product labels or peer-reviewed literature.  Where adequate clinical data exists for the concomitant use of two 
previously approved drugs or biologics, a sponsor seeking approval for the drug and biologic combination should 
contact the appropriate review division to discuss whether any additional nonclinical data are warranted. 
  2 Contains Nonbinding Recommendations 
 
A.  Safety Considerations 
 
If existing clinical and nonclinical safety data for each separate drug or biologic are sufficient to 
support the safety of the proposed new indication, then the FDA recommends that the following 
factors relevant to the safety of the combination be considered to determine whether further 
nonclinical studies are warranted.  
 
1.  Information available on prior human experience with the combination.  The FDA 
recommends that the sponsor provide a summary of the available data in humans (if any) 
on the use of the combination.  The FDA also encourages the sponsor to provide copies 
of any relevant published studies in humans (or animals).  Such reports may not provide 
definitive safety data, but they may provide some measure either of assurance or reasons 
for concern. 
 
2.  Information known about the individual drugs or biologics in animals and humans and 
concordance of pharmacokinetics (PK), pharmacodynamics (PD), and toxicologic effects 
in animals with the analogous data for humans. 
 
3.  Possibility of a PD interaction.  Drugs/biologics may exhibit affinity for the same 
receptors or biologic targets or may produce similar effects on physiologic function, 
related or not to their mechanism of action.   
 
4.  Possibility of a PK interaction.  A PK interaction can manifest in several ways, some of 
which can be monitored in vivo and some of which cannot.  One drug/biologic product 
may alter the absorption or excretion of another product, change its distribution into one 
or more tissues, or change its pattern or rate of metabolism.  Drugs may compete for 
serum protein binding, resulting in an increase in circulating free levels and tissue uptake 
of one drug.   
 
5.  Possibility of a toxicologic interaction (i.e., that the target organs for toxicity are similar 
for each drug/biologic).  This situation may result in a lowering of the previously 
determined no-effect doses for one or both drug/biologic products and more severe 
toxicities in the affected organs.  The FDA will consider all known toxicology on the 
product (e.g., general toxicity, reproductive toxicity, carcinogenicity, and safety 
pharmacology studies (cardiovascular, central nervous system (CNS), respiratory)).   
 
6.  Margin of safety for each drug/biologic product.  If one or more of the drugs/biologics 
has a narrow margin of safety (i.e., causes serious toxicity at exposures close to the 
predicted clinical exposure), then the possibility of drug interaction is of particular 
concern, especially if the toxicity is not reversible or cannot be monitored clinically. 
 
7.  Possibility that the drugs/biologics compete for or alter the activity or endogenous levels 
of the same enzymes or other intracellular molecules (e.g., co-administration of two pro-
oxidants could deplete endogenous levels of glutathione). 
 
  3 Contains Nonbinding Recommendations 
8.  Possibility of a chemical interaction.  One drug may chemically modify another drug or 
biologic (e.g., one drug may oxidize, methylate, or ethylate the other drug or biologic).  
This could result in NMEs with new toxicities. 
 
9.  Possibility that one drug/biologic may compromise the effectiveness of another 
drug/biologic for a lifesaving therapy. 
 
B.  Nonclinical Study Recommendations/General Procedure 
 
If existing clinical and nonclinical safety data for each separate drug or biologic are sufficient to 
support the safety of the proposed new indication, including the dose, dosing schedule, duration, 
and new patient population, then additional nonclinical studies may not be needed.  
 
The general approach to addressing the safety concerns posed by the testing or marketing of 
combinations of previously marketed drugs or biologics is illustrated in Figure A.  The safety of 
the combination should be assessed according to the factors listed in section II.A (see Figure A, 
Boxes 1 to 2).  If neither individual drug or biologic product has serious toxicity at exposures 
well above the proposed clinical exposure or if there is substantial clinical experience with the 
combination, the FDA may recommend that additional nonclinical studies do not need to be 
conducted before testing in humans, during initial studies in humans, or at all (Boxes 2 to 3).  
The Agencys recommendation to conduct nonclinical studies for further development of the 
combination will depend on what is learned from initial studies in humans or what is known 
from prior human use of the combination.7
 
If after evaluating the available data on the individual drug/biologic products and the potential 
for drug/biologic interaction there is no evidence to suggest a possible interaction, direct 
assessment of the combination by testing in animals may not be needed before the first small 
clinical studies with the combination.  Even if an interaction is expected, nonclinical studies may 
not be necessary if the expected interaction is likely to result in predictable, nonserious, 
monitorable effects in humans.  For example, if a metabolic interaction is predicted, the starting 
dose could be significantly lowered in humans.  Metabolic interactions have been seen for 
combinations of two biologics.  There is a possibility of drugs/biologics affecting the same tissue 
or biologic target or having a PD interaction. 
 
Generally, the FDA recommends that sponsors conduct nonclinical toxicity studies before 
clinical studies are initiated if: (1) the drug products have similar target organ toxicity or PD 
activity; and (2) either drug product causes serious or nonmonitorable toxicity in animals or 
humans at exposures near the clinical exposure; or (3) any other reason exists for serious clinical 
concern (see section II.A).  The particular nonclinical studies recommended by the FDA will 
depend on a number of factors, including the nature of the toxicity and on the concerns identified 
in section II.A.  For assessment of general toxicity, a bridging study may be appropriate, 
provided the duration is sufficient to elicit the toxicity of concern.  For example, a general 
                                                 
7 For example, as previously mentioned, the draft HIV guidance discusses the FDAs belief that certain antiretroviral 
therapies previously approved for the treatment of HIV may be approved for concomitant use without additional 
nonclinical (or clinical) studies, because the clinical safety and efficacy of concomitant use have been evaluated and 
described in product labels or peer-reviewed literature.   
  4 Contains Nonbinding Recommendations 
toxicity bridging study of 3 months duration could be considered for a chronic indication.  The 
FDA suggests that combination studies include an assessment of several dose levels of the 
combination and a high dose of each drug alone.  Other possible designs can be discussed with 
the review division.  Sponsors are urged to select the doses of each drug used in combination to 
allow for additive or synergistic effects without unacceptable toxicity in the high-dose groups.  
Usually, assessment of the drug combination may be conducted in only one species if one of the 
following conditions exists: (1) toxicity in a particular species has high concordance with human 
toxicity or the toxicities are similar among species; or (2) one species is a more relevant model 
for human risk based on other factors such as PK/ADME (absorption, distribution, metabolism, 
and excretion) or expression of the pharmacologic activity.  If a sponsor will be conducting only 
one general toxicity study, the FDA recommends that the sponsor provide justification for the 
species selected for testing the combination.  There may be cases, however, in which the Agency 
may recommend conducting studies in two species despite one or both of these conditions being 
met.  For example, depending on the results in the first species, a new cause for concern might 
warrant follow-up studies in a second species, if there is an appropriate second species. 
 
Sometimes one of the drugs proposed for the combination will be much more toxic in animals 
than in humans, such that animals cannot tolerate the combination at doses that produce exposure 
relevant to the anticipated clinical exposure (e.g., some nonsteroidal anti-inflammatory drugs 
(NSAIDs) and antibiotics).  In those cases, general toxicity studies of the combination could be 
conducted at a dose giving less exposure than that achieved with the recommended clinical dose 
of the more toxic drug product, provided that a serious dose-limiting toxicity is achieved in the 
animals.  The timing of the studies should be as described in the ICH guidance for industry M3 
Nonclinical Safety Studies for the Conduct of Human Clinical Trials for Pharmaceuticals.   
 
Combination genotoxicity studies generally will not be necessary if the individual agents have 
been tested consistent with current standards.  Embryo-fetal development studies of the 
combination should be conducted per the timing described in ICH M3, unless the marketed 
products are already known to have significant risk for developmental toxicity (e.g., one of the 
marketed drugs has been assigned a pregnancy category D or X).  If combination studies are 
needed, a single study could be conducted in the most appropriate species, based on what is 
known about the individual drugs or biologics.  If a significant risk is only identified for a 
particular trimester of pregnancy, such as ACE inhibitors during the third trimester, studies to 
evaluate the effects of exposure to the NME or the combination during other trimesters may be 
needed. 
 
For chronic indications, a carcinogenicity study on the drug combination generally will only be 
recommended if statistically significant incidences of preneoplastic lesions were observed at a 
new organ or tissue site in nonclinical studies of the combination.  Results of the nonclinical 
studies may be used to recommend modification of the clinical protocol (e.g., starting clinical 
doses, parameters to monitor) (Box 8). 
 
 
  5 Contains Nonbinding Recommendations 
III.  NONCLINICAL STUDIES FOR A COMBINATION OF DRUGS OR BIOLOGICS 
WHEN ONE OR MORE IS PREVIOUSLY MARKETED AND ONE IS A NEW 
MOLECULAR ENTITY (FIGURE B) 
 
This section addresses the situation in which a sponsor submits an application to develop a 
combination of two or more drugs or biologics  one or more previously marketed and one an 
NME or a combination of drugs and biologics.  
 
A.  General Toxicology Studies  
 
The Agency generally suggests that nonclinical studies be conducted on the NME for a product 
that is a combination of an NME and a previously marketed drug or biologic.  The FDA believes 
that the standard battery of nonclinical studies (i.e., genetic toxicology, pharmacology, safety 
pharmacology, PK/ADME, general toxicity, reproductive and developmental toxicity, 
carcinogenicity) generally will be appropriate for the NME, as described in ICH M3.  ICH S6 
should be consulted for nonclinical development of biologic products.  If genotoxicity studies on 
the previously marketed product are consistent with current standards, it may be appropriate to 
conduct genotoxicity studies on only the drug NME portion of the combination.   
 
Depending on the duration of the proposed therapy, the FDA recommends that a sponsor conduct 
a bridging study of up to 90 days with the combination in the most appropriate species.  Studies 
of shorter duration could be appropriate for shorter clinical studies or for nonchronic indications, 
per ICH M3.  There may be cases, however, where studies in a second species may be 
appropriate.  Because the drug ratio may change during drug development, it is important to 
design the toxicity studies to provide adequate margins of safety for future clinical studies.  For 
combinations, the FDA recommends that the exposure to the drugs/biologics be at ratios that are 
relevant to the intended clinical use. 
 
Sometimes one of the drugs proposed for the combination will be much more toxic in animals 
than in humans, such that animals cannot tolerate the combination at doses that produce exposure 
relevant to the anticipated clinical exposure (e.g., some NSAIDs and antibiotics).  In those cases, 
nonclinical studies of the combination could be conducted at a dose giving less exposure than 
that achieved with the recommended clinical dose of the more toxic drug product, provided that a 
serious dose-limiting toxicity is achieved in the animals.  
 
B.  Reproductive and Developmental Toxicology 
 
Embryo-fetal development studies on the NME are recommended, as are fertility and other 
reproduction studies, by the ICH.  Studies to evaluate the reproductive toxicity of the 
combination are not generally needed.  Embryo-fetal development studies of the combination 
should be conducted unless the marketed drug substance or the NME is already known to have 
significant risk for developmental toxicity (e.g., the marketed drug has been assigned a 
pregnancy category D or X).  If combination studies are needed, a single study could be 
conducted in the most appropriate species, based on what is known about the individual drugs or 
biologics.  If a significant risk is only identified for a particular trimester of pregnancy, such as 
  6 Contains Nonbinding Recommendations 
ACE inhibitors during the third trimester, studies to evaluate the effects of exposure to the NME 
or the combination during other trimesters may be needed. 
 
C.  Animal Models of Efficacy 
 
Animal models of efficacy are not generally needed.  However, valuable data may be obtained 
from studying the combination in appropriate animal models of efficacy, if they are available and 
considered relevant.  For example, there are situations in which one drug has been shown to alter 
the efficacy of the second drug.  This information may be important if one or more of the drugs 
in the combination is for a serious or life-threatening indication.  Identifying such an interaction 
permits an informed choice of dose of each product in the combination and an optimal schedule 
for the proposed clinical trial. 
 
D.  Further Studies  
 
The FDA recommends that a sponsor address any important data gaps for the marketed product 
or products that may be relevant for the proposed indication.  After evaluating the available data 
on the individual drug products and the data on the bridging study of up to 90 days on the 
combination, a determination will be made on whether it is appropriate to conduct additional 
studies to address potential drug/biologic interactions.  If a drug interaction is identified in the 
bridging study (synergistic effects) and the mechanism (e.g., PK, PD, or overlapping toxicity) is 
not apparent, then the FDA urges sponsors to consider studies to understand the nature of the 
interaction.  The possible mechanisms of drug interaction listed in section II.A would also apply 
to combinations of one or more previously marketed drugs/biologics and an NME.  Other than 
the general toxicology bridging study of up to 90 days and studies on embryo-fetal development, 
additional studies on the combination generally will not be needed. 
 
 
IV.  NONCLINICAL STUDIES FOR A COMBINATION OF TWO OR MORE 
DRUGS OR BIOLOGICS WHEN ALL ARE NEW MOLECULAR ENTITIES 
(FIGURE C) 
 
A.  General Toxicology Studies  
 
The FDA generally recommends that the sponsor conduct nonclinical studies on each NME to 
evaluate the safety of a combination of NMEs.  Sponsors are encouraged to conduct the standard 
battery of nonclinical studies (i.e., genetic toxicology, pharmacology, safety pharmacology, 
PK/ADME, general toxicity, reproductive and developmental toxicity, carcinogenicity) on each 
NME, according to the timing as described in ICH M3, and according to ICH S6 for nonclinical 
development of biologic products.  Depending on the duration of the proposed therapy, a 
bridging study of up to 90 days (for chronic indications) should be conducted with the 
combination in the most appropriate species if the NMEs were evaluated as separate entities 
(which is preferred) and not as a combination.  There may be cases, however, where studies in a 
second species may be appropriate.  If the two drugs or biologics are proposed to be marketed 
together only, then it is possible that it may be sufficient to conduct toxicology studies only on 
the combination.  However, nonclinical studies conducted on each NME alone can be invaluable 
  7 Contains Nonbinding Recommendations 
should it become important to alter the clinical regimen from what is initially proposed or 
studied. 
 
Because the drug ratio may change during drug development, it is important to design the 
toxicity studies to provide adequate margins of safety for future clinical studies.  The FDA 
recommends that the drugs or biologics be tested at doses that produce exposure ratios that are 
relevant (i.e., somewhat similar) to the intended clinical use, when feasible. 
 
Sometimes one of the drugs proposed for the combination will be much more toxic in animals 
than in humans, such that animals cannot tolerate the combination at doses that produce exposure 
relevant to the anticipated clinical exposure (e.g., some NSAIDs and antibiotics).  In those cases, 
nonclinical studies of the combination might be conducted at a dose giving less exposure than 
that achieved with the recommended clinical dose of the more toxic drug, provided that a serious 
dose-limiting toxicity is achieved in the animals at the highest dose.  
 
B.  Animal Models of Efficacy 
 
Animal models of efficacy are not generally needed.  However, valuable data may be obtained 
from studying the combination in appropriate animal models of efficacy, if they are available and 
considered relevant.  For example, there are situations in which one drug has been shown to alter 
the efficacy of the second drug.  This information is especially important if one or more of the 
drugs or biologics in the combination is for a serious or life-threatening indication.  Identifying 
such an interaction permits an informed choice of dose of each product in the combination and 
an optimal schedule for the proposed clinical trial. 
 
C.  Safety Pharmacology 
 
The FDA strongly recommends that sponsors assess the effects of drugs/biologics on a variety of 
organ systems before dosing in humans.  Combination safety pharmacology studies of a 
particular organ system (e.g., cardiac, respiratory, CNS) may be valuable in many situations, 
such as when both drugs target the same organ system, a toxicity is associated with a class of 
compounds (e.g., QT prolongation), or the intended patient population is compromised (e.g., 
renal impairment).  Sometimes when the molecular target is known, effects of the combination 
can be predicted. 
 
D.  PK/ADME and Toxicokinetics  
 
The FDA recommends that sponsors conduct combination PK/ADME studies to assess the 
potential for a PK interaction between the drugs/biologics.  These data are valuable for 
supporting the safety profile and guiding the drug/biologic development process.  The FDA 
further recommends that PK/ADME combination studies (e.g., in vitro drug metabolism studies) 
be conducted early in drug development.  The FDA encourages sponsors to evaluate serum 
protein binding and to monitor plasma concentrations of each drug in the toxicology studies.  It 
may be possible to collect PK data as part of the toxicology studies instead of in a separate study.  
 
  8 Contains Nonbinding Recommendations 
E.  Genetic Toxicology  
 
Genetic toxicology studies are not needed for biologic or drug/biologic combinations.  Assessing 
the genotoxic potential of a drug/drug combination is generally not necessary, provided that 
adequate studies of the individual drug substances have been conducted.  For the in vitro assays, 
genotoxic potential is routinely tested in the absence and presence of metabolic activation.  
Therefore, testing drugs in combination in these assays would not likely provide additional 
information to assays testing each drug alone, particularly if any potential interaction is expected 
to be from effects on hepatic metabolism.   
 
F.  Special Toxicology  
 
The FDA may recommend that a sponsor conduct special toxicology studies, such as local 
tolerance studies, with the NME as well as with the combination in a particular therapeutic area 
relevant to the proposed use.  The Agency may also recommend that targeted toxicity studies be 
conducted, depending upon the nature of toxicities seen in animals and humans with the drug 
products or drug class.   
 
G.  Reproductive and Developmental Toxicology 
 
Embryo-fetal development studies on each NME are generally recommended by the ICH, as are 
fertility and other reproduction studies.  Studies to evaluate the reproductive toxicity of the 
combination are not generally needed, if this has been evaluated for the individual NME.  If 
developmental toxicity has been assessed only on each NME separately, then the FDA 
recommends that developmental toxicity studies be conducted on the combination as well, in the 
most appropriate species, before treatment of women of childbearing potential.  Embryo-fetal 
developmental studies of the combination may not be needed if one of the NMEs is known from 
the nonclinical studies to have significant risk for developmental toxicity, such as results 
indicating potential labeling as a D or X.  If a significant risk is only indicated for a 
particular trimester of pregnancy, studies to evaluate the effects of exposure to the combination 
during other trimesters may be needed. 
 
H.  Further Studies   
 
After evaluating the available data on the individual drug/biologic products and the data on the 
bridging study of up to 90 days on the combination, a determination will be made as to whether 
it is appropriate to conduct additional studies to address potential drug/biologic interactions.  If a 
drug/biologic interaction is identified in a study and the mechanism (e.g., PK, PD, or overlapping 
toxicity) is not apparent, then the FDA urges the sponsor to consider studies to evaluate the 
nature of the interaction.  The possible mechanisms of drug/biologic interaction listed in section 
II.A would also apply to combinations of more than one NME.  Generally, studies of the 
combination other than the general toxicology bridging study of up to 90 days (depending on the 
chronicity of the indication) and studies on embryo-fetal development will not be needed.   
 
  9 Contains Nonbinding Recommendations 
I.  Carcinogenicity 
 
Depending on the duration and intended use of the combination, the Agency may suggest that the 
sponsor conduct carcinogenicity studies on the combination, if each individual NME has not 
been tested for carcinogenicity.   
 
 
  10 Contains Nonbinding Recommendations 
APPENDIX:  RECOMMENDED GENERAL PROCEDURES 
 
Figure A:  Combinations of Previously Marketed Drugs or Biologics 
 
 
 
1.* Evaluate each individual drug/biologic (section II.A).
 
 
 
 
 
 
2. Concern about combina-
  No 
tion based on factors in  
  3. Proceed with 
section II.A (e.g., PK, PD, 
  or toxicologic interaction;   clinical study. 
 
toxicity that cannot be 
 
       monitored)? 
 
  5. Evaluate in  No 
  vitro metabo-
Yes 
  lism data; if 
  not available, 
  conduct in 
6. Metabolic 
  Yes vitro metab-
interaction? 
4. Concern limited to 
  olism studies 
metabolic interaction? 
  (in vitro may 
  not be 
  appropriate for 
  biologics). 
  Yes 
  No 
 
  8. Adjust clinical study 
7. Conduct toxicology studies on 
  design as appropriate. 
combination to address concerns. 
 
 
 
 
 
 
 
*
Box numbers correspond to references in the text 
document and do not depict the order in which one 
proceeds. 
 
  11 Contains Nonbinding Recommendations 
Figure B:  Combinations of Previously Marketed Drugs or Biologics with NMEs 
 
 
 
 
Evaluate each individual drug or biologic (ICH); address data gaps 
 
(i.e., generally all studies recommended for NME). 
 
 
 
  Usually conduct toxicology study of up to 90 days (shorter durations for shorter 
clinical use and nonchronic indications) and embryo-fetal developmental study on 
 
combination; see the text for details on determining whether other studies are 
 
appropriate. 
 
 
 
 
 
If nature of interaction is 
  Do toxicology  Yes
not apparent, consider 
  studies suggest an 
studies to understand the 
  interaction? 
interaction. 
 
 
 
 
       No 
 
 
 
 
Proceed with clinical study at doses 
 
derived from toxicology studies. 
 
 
 
 
 
 
 
 
 
 
 
 
  12 Contains Nonbinding Recommendations 
Figure C:  Combinations of NMEs with NMEs 
 
 
 
  Preferably, evaluate each NME (ICH) before evaluating the combination.  Usually conduct 
  toxicology study of up to 90 days and embryo-fetal developmental study on combination (see the 
  text for details).  If only individual NMEs are studied, use the following approach to address safety 
  concerns. 
 
 
 
 
 
 
  Proceed with clinical 
No 
Concern about 
  study at doses derived 
combination based on 
  from toxicology studies. 
factors in section II.A? 
 
 
Evaluate in 
vitro metab-
Yes No
olism data; if 
not available, 
Yes conduct in 
Metabolic 
Concern about a 
vitro metab-
interaction? 
metabolic 
olism studies 
interaction? 
(in vitro may 
not be 
appropriate for 
biologics).  Yes 
No 
Conduct PK 
Conduct toxicology studies to  clinical study.  
address concerns other than PK? 
Adjust clinical 
study design as 
appropriate. 
  13