Guidance for Industry, 
Investigators, and Reviewers 
 
Exploratory IND Studies  
 
 
 
 
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
U.S. Department of Health and Human Services 
Food and Drug Administration 
Center for Drug Evaluation and Research (CDER) 
 
January 2006 
Pharmacology/Toxicology 
 
G:\7086fnl.doc 
12/29/05  Contains Nonbinding Recommendations 
 
Guidance for Industry, 
Investigators, and Reviewers 
 
Exploratory IND Studies  
 
 
 
Office of Training and Communication 
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) 
 
January 2006 
Pharmacology/Toxicology 
 
  Contains Nonbinding Recommendations 
 
TABLE OF CONTENTS 
 
 
 
I.  INTRODUCTION.............................................................................................................1 
II.  BACKGROUND...............................................................................................................2 
A.  Traditional Phase 1 Approach......................................................................................................2 
B.  Exploratory IND Approach..........................................................................................................3 
III.  CONTENT OF IND SUBMISSIONS.............................................................................5 
A.  Clinical Information......................................................................................................................5 
1. Introductory statement and general investigational plan................................................................5 
2. Types of studies................................................................................................................................5 
B.  Chemistry, Manufacturing, and Controls Information.............................................................6 
1. General information for the candidate product...............................................................................6 
2. Analytical characterization of candidate product...........................................................................8 
C.  Safety Program Designs  Examples..........................................................................................8 
1. Clinical studies of pharmacokinetics or imaging............................................................................9 
2. Clinical trials to study pharmacologically relevant doses.............................................................10 
3. Clinical studies of MOAs related to efficacy.................................................................................11 
D.  GLP Compliance..........................................................................................................................12 
IV.  CONCLUSION...............................................................................................................12 
ATTACHMENT.........................................................................................................................13 
  Contains Nonbinding Recommendations 
Guidance for Industry and Reviewers1 
 
Exploratory IND Studies  
 
 
 
 
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.  
Alternative approaches can be used if the approach satisfies the requirements of the applicable statutes 
and regulations. Discussions of an alternative approaches can be scheduled by contacting the FDA staff 
responsible for implementing this guidance.  If the appropriate FDA staff cannot be located, contact can 
be made using the telephone number listed on the title page of this guidance.  
 
 
 
 
 
I.  INTRODUCTION  
 
This guidance is intended to clarify what preclinical and clinical approaches, as well as 
chemistry, manufacturing, and controls information, should be considered when planning 
exploratory studies in humans, including studies of closely related drugs or therapeutic biological 
products, under an investigational new drug (IND) application (21 CFR 312).  Existing 
regulations allow a great deal of flexibility in the amount of data that needs to be submitted with 
an IND application, depending on the goals of the proposed investigation, the specific human 
testing proposed, and the expected risks. The Agency believes that sponsors have not taken full 
advantage of that flexibility and often provide more supporting information in INDs than is 
required by regulations.  This guidance is intended to clarify what manufacturing controls, 
preclinical testing, and clinical approaches can be considered when planning limited, early 
exploratory IND studies in humans.   
 
For the purposes of this guidance the phrase exploratory IND study is intended to describe a 
clinical trial that  
- is conducted early in phase 1, 
- involves very limited human exposure, and 
- has no therapeutic or diagnostic intent (e.g., screening studies, microdose studies). 
 
                                                 
1 This guidance was developed by the Office of New Drugs in the Center for Drug Evaluation and Research 
(CDER).  
 
This guidance contains information collection provisions that are subject to review by the Office of Management 
and Budget under the Paperwork Reduction Act of 1995 (44 U.S.C. 3501-3520).  The collection of information in 
this guidance has been approved under OMB Control No. 0910-0014. 
 
  1 Contains Nonbinding Recommendations 
Such exploratory IND studies are conducted prior to the traditional dose escalation, safety, and 
tolerance studies that ordinarily initiate a clinical drug development program.  The duration of 
dosing in an exploratory IND study is expected to be limited (e.g., 7 days).  This guidance 
applies to early phase 1 clinical studies of investigational new drug and biological products that 
assess feasibility for further development of the drug or biological product.2  
 
FDA's guidance documents, including this guidance, do not establish legally enforceable 
responsibilities.  Instead, guidances describe the Agency's current thinking on a topic and should 
be viewed only as recommendations, unless specific regulatory or statutory requirements are 
cited.  The use of the word should in Agency guidances means that something is suggested or 
recommended, but not required. 
 
 
II.  BACKGROUND 
 
In its March 2004 Critical Path Report,3 the Agency explained that to reduce the time and 
resources expended on candidate products that are unlikely to succeed,4 new tools are needed to 
distinguish earlier in the process those candidates that hold promise from those that do not.  This 
guidance describes some early phase 1 exploratory approaches that are consistent with regulatory 
requirements while maintaining needed human subject protection, but that involve fewer 
resources than is customary, enabling sponsors to move ahead more efficiently with the 
development of promising candidates.  
 
A.  Traditional Phase 1 Approach 
 
Typically, during pharmaceutical development, large numbers of molecules are generated with 
the goal of identifying the most promising candidates for further development.  These molecules 
are generally structurally related, but can differ in important ways.  Promising candidates are 
often selected using in vitro testing models that examine binding to receptors, effects on enzyme 
activities, toxic effects, or other in vitro pharmacologic parameters; these tests usually require 
only small amounts of the drug.  Candidates that are not rejected during these early tests are 
prepared in greater quantities for in vivo animal testing for efficacy and safety.  Commonly, a 
single candidate is selected for an IND application and introduction into human subjects, initially 
healthy volunteers in most cases.  
 
Before the human studies can begin, an IND must be submitted to the Agency containing, among 
other things, information on any risks anticipated based on the results of pharmacologic and 
                                                 
2 Specifically, this guidance is limited to drug and certain well-characterized therapeutic biological products (e.g., 
recombinant therapeutic proteins and monoclonal antibodies) regulated by CDER.  The guidance does not apply to 
human cell or tissue products, blood and blood proteins, vaccines, or to products regulated as devices.   
 
3 Innovation or Stagnation, Challenge and Opportunity on the critical Path to New Medical Products (March 2004). 
 
4 "A new medical compound entering phase 1 testing, often representing the culmination of upwards of a decade of 
preclinical screening and evaluation, is estimated to have only an 8 percent chance of reaching the market," Critical 
Path Report, March 2004. 
 
  2 Contains Nonbinding Recommendations 
toxicological data collected during studies of the drug in animals (21 CFR 312.23(a)(8)).  These 
basic safety tests are most often performed in rats and dogs.  The studies are designed to permit 
the selection of a safe starting dose for humans, to gain an understanding of which organs may be 
the targets of toxicity, to estimate the margin of safety between a clinical and a toxic dose, and to 
predict pharmacokinetic and pharmacodynamic parameters.  These early tests are usually 
resource intensive, requiring significant investment in product synthesis, animal use, laboratory 
analyses, and time.  Many resources are invested in, and thus wasted on, candidate products that 
subsequently are found to have unacceptable profiles when evaluated in humans  less than 10 
percent of INDs for new molecular entities (NME) progress beyond the investigational stage to 
submission of a marketing application (NDA).3  In addition, animal testing does not always 
predict performance in humans, and potentially effective candidates may not be developed 
because of resource constraints.  
 
Existing regulations allow a great deal of flexibility in terms of the amount of data that need to 
be submitted with any IND application, depending on the goals of the proposed investigation, the 
specific human testing proposed, and the expected risks.  The Agency believes that sponsors 
have not taken full advantage of that flexibility.  As a result, limited, early phase 1 studies, such 
as those described in this guidance, are often supported by a more extensive preclinical database 
than is required by the regulations.   
 
This guidance describes preclinical and clinical approaches, and the chemistry, manufacturing, 
and controls information that should be considered when planning exploratory IND studies in 
humans, including studies of closely related drugs or therapeutic biological products, under a 
single IND application (21 CFR 312).   
 
B.  Exploratory IND Approach 
 
Exploratory IND studies usually involve very limited human exposure and have no therapeutic 
or diagnostic intent.  Such studies can serve a number of useful goals.  For example, an 
exploratory IND study can help sponsors 
  
  Determine whether a mechanism of action defined in experimental systems  can also be 
observed in humans (e.g., a binding property or inhibition of an enzyme) 
  Provide important information on pharmacokinetics (PK) 
  Select the most promising lead product from a group of candidates5 designed to interact 
with a particular therapeutic target in humans, based on PK or pharmacodynamic (PD) 
properties 
                                                 
5 For the purposes of this guidance, the term candidate, or candidate product, is used to describe a drug or biologic 
that is being tested in early exploratory studies under an IND.  This guidance does not distinguish between a drug 
product and a drug substance as some other Agency guidances do.  
 
(Most guidances use the term drug product to refer to a finished dosage form (e.g., tablet, capsule, solution) that 
contains an active drug ingredient generally, but not necessarily, in association with inactive ingredients, or a 
finished dosage form that does not contain an active ingredient but is intended to be used as a placebo.  Drug 
substance usually refers to any component that is intended to furnish pharmacological activity or other direct effect 
  3 Contains Nonbinding Recommendations 
  Explore a products biodistribution characteristics using various imaging technologies   
Whatever the goal of the study, exploratory IND studies can help identify, early in the process, 
promising candidates for continued development and eliminate those lacking promise.  As a 
result, exploratory IND studies may help reduce the number of human subjects and resources, 
including the amount of candidate product, needed to identify promising drugs. The studies 
discussed in this guidance involve dosing a limited number of subjects with a limited range of 
doses for a limited period of time.   
 
Existing regulations provide more flexibility with regard to the preclinical testing requirements 
for exploratory IND studies than for traditional IND studies.  However, sponsors submitting the 
kinds of studies described in this guidance have not always taken full advantage of that 
flexibility.  Sponsors often provide more supporting information in their INDs than is required 
by the regulations.  Because exploratory IND studies involve administering either sub-
pharmacologic doses of a product, or doses expected to produce a pharmacologic, but not a toxic, 
effect, the potential risk to human subjects is less than for a traditional phase 1 study that, for 
example, seeks to establish a maximally tolerated dose.  Because exploratory IND studies 
present fewer potential risks than do traditional phase 1 studies that look for dose-limiting 
toxicities, such limited exploratory IND investigations in humans can be initiated with less, or 
different, preclinical support than is required for traditional IND studies.6   
 
The Agency expects that this early phase 1 exploratory IND approach will apply to a number of 
different study paradigms.  Although his guidance explores several potential applications, many 
others can be proposed.  The Agency believes that, consistent with its Critical Path Initiative, 
clarifying Agency thinking about how much and what kind of testing is needed to support early 
studies in humans will facilitate the entry of new products into clinical testing and speed product 
development. 
 
Although exploratory IND studies may be used during development of products intended for any 
indication, it is particularly important for manufacturers to consider this approach when 
developing products to treat serious diseases.  Because the approach can help identify promising 
candidates more quickly and precisely, exploratory IND studies could become an important part 
of the armamentarium when developing drug and biological products to treat a serious or life-
threatening illness.  The Agency has previously articulated its commitment to ensuring that 
appropriate flexibility is applied when patients with a serious disease and no satisfactory 
alternative therapies are enrolled in a trial with therapeutic intent.7 
 
                                                                                                                                                             
in the diagnosis, cure, mitigation, treatment, or prevention of disease, or to affect the structure or any function of the 
body.)  
 
6 Generally, these types of studies would not be carried out in pediatric patients or in pregnant or lactating women. 
 
7 Subpart H Accelerated  Approval of New Drugs for Serious or Life-Threatening Illnesses.  See also FDA guidance 
for industry Fast Track Drug Development Programs  Designation, Development, and Application Review.  
 
  4 Contains Nonbinding Recommendations 
III.  CONTENT OF IND SUBMISSIONS 
 
To begin any kind of testing in humans, applicants must submit an IND application to the 
Agency with certain types of information (see 21 CFR 312.23 IND Content and Format).  The 
primary purpose of the IND submission is to ensure that subjects will not face undue risk of 
harm.  The major information that must be submitted includes:  
 
  Information on a clinical development plan  
  Chemistry, manufacturing, and controls information 
  Pharmacology and toxicology information  
  Previous human experience with the investigational candidate or related compounds, 
if there is any 
 
The following sections discuss the first three in more detail.  Because the exploratory IND 
studies addressed by this guidance will be first in human studies, previous human experience is 
not pertinent and will not be discussed.  The common theme throughout is that, depending on the 
study, the informational requirements for exploratory IND studies are more flexible than for 
traditional IND studies.  
 
A.  Clinical Information 
 
1.  Introductory statement and general investigational plan 
 
A traditional IND application describes the rationale for the proposed clinical trial program and 
discusses the potential outcome of the clinical investigation.  The exploratory IND studies 
discussed here focus on a circumscribed study or group of studies, and plans for further 
development cannot be formulated without the results of these studies.  Therefore, an exploratory 
IND application should articulate the rationale for selecting a compound (or compounds) and for 
studying them in a single trial or related trials, as this represents all that is known about the 
overall development plan at this stage.  This section should also make it clear that the IND is 
intended to be withdrawn8 after completion of the outlined study or studies. 
 
2.  Types of studies  
 
Potentially useful study designs include both single- and multiple-dose studies.  In single-dose 
studies, a sub-pharmacologic9 or pharmacologic dose is administered to a limited number of 
subjects (healthy volunteers or patients).  For example, microdose studies usually involve the 
single administration of a small dose with the goal of collecting pharmacokinetic information or 
performing imaging studies, or both. 
                                                 
8 The withdrawn, or inactive, IND can be referenced in any subsequent traditional IND. 
 
9 A radiolabeled candidate compound can be administered at doses that are known to have no pharmacologic effect 
in humans without an IND application in basic research studies when the compound has previously been studied in 
humans and the results published in the literature.  These basic research investigations are conducted under the 
oversight of an institutional review board (IRB) and a radioactive drug research committee (21 CFR 361.1).  
 
  5 Contains Nonbinding Recommendations 
 
Repeat dose clinical studies can be designed with pharmacologic or pharmacodynamic 
endpoints.  In exploratory IND studies, the duration of dosing should be limited (e.g., 7 days).  
For escalating dose studies done under an exploratory IND, dosing should be designed to 
investigate a pharmacodynamic endpoint, not to determine the limits of tolerability.   
 
B.  Chemistry, Manufacturing, and Controls Information 
 
The regulations at 21 CFR 312.23(a)(7)(i) emphasize the graded nature of chemistry, 
manufacturing, and controls (CMC) information needed as development under an IND 
application progresses.  Although in each phase of a clinical investigational program sufficient 
information should be submitted to ensure the proper identification, strength, quality, purity, and 
potency of the investigational candidate, the amount of information that will provide that 
assurance will vary with the phase of the investigation, the proposed duration of the 
investigation, the dosage form, and the amount of information already available.  For the purpose 
of an exploratory IND application, the CMC information indicated below can be provided in a 
summary report to enable the Agency to make the necessary safety assessment.   
 
The sponsor must state in the beginning of the exploratory IND application whether it believes 
the chemistry or manufacturing of the candidate product presents any potential for human risk 
(e.g., specific findings in preclinical studies associated with known risks of related compounds) 
( 312.23).  If so, these potential risks should be discussed, and the steps proposed to monitor for 
such risks should be described.  
 
The Agency is in the process of developing guidance explaining the stepwise approach to 
meeting current good manufacturing practice (CGMP) regulations.  Once finalized, that guidance 
will be useful to persons seeking to manufacture, or prepare, products intended for use in an 
exploratory IND study.  
  
1.  General information for the candidate product 
 
Except as noted below, the extent and type of chemistry and manufacturing information to be 
submitted in an exploratory IND application is similar to that described in current guidance for 
use of investigational products.10  Information on each candidate product (i.e., the active 
ingredient) can be submitted in a summary report containing the following items.  
 
  Description of the candidate product, including physical, chemical, and/or biological 
characteristics, as well as its source (e.g., synthetic, animal source, plant extract, or 
biotechnology-derived) and therapeutic class (e.g., radiopharmaceutic, 
immunosuppressant, agonist, antagonist) (see sections below for exceptions).  
  Description of the dosage form and information related to the dosage form 
                                                 
10 See guidance for industry Content and Format of Investigational New Drug Applications for Phase 1 Studies of 
Drugs, Including Well-Characterized, Therapeutic, Biotechnology-Derived Products. 
 
  6 Contains Nonbinding Recommendations 
  Description of the formulation or routes of administration intended to be used in the 
human trial.  For oral administration, sponsors can consider using suspensions or 
solutions in addition to the more usual tablets, powders, and capsules.  For products 
intended for ophthalmic, inhalational (aqueous base), or parenteral administration, 
sterility and apyrogenicity must be ensured.  For biological candidate products, freedom 
from contaminants associated with their manufacture, such as viruses, mycoplasma, and 
foreign DNA, also should be ensured.  All excipients should be generally recognized as 
safe11 or part of a formulation that is approved or licensed in the United States for the 
same route of administration and amount,12 or adequately qualified through appropriate 
animal studies. 
  The grade and quality (e.g., USP, NF, ACS) of excipients used in the manufacture of the 
investigational candidate product, including both those components intended to appear in 
the product and those that may not appear, but that are used in the manufacturing process 
  Name and address of the manufacturer(s) (if different from the sponsor) 
 
  The method of preparation of the candidate product lots used in preclinical studies and 
intended for the proposed human study, including a brief description of the method of 
manufacture and the packaging procedure, as appropriate, with a description of the 
container and closure system.  For the active substance, include a list of the starting 
materials, reagents, solvents, catalysts used, and purification steps employed to prepare 
the candidate product.  For sterile products, describe the sterilization process and controls 
for ensuring sterility.  For biological/biotechnology-derived products, also identify the 
source material (e.g., Master Cell Bank), describe the expression system (e.g., 
fermentation methods) and harvest methods, as well as methods for removal/inactivation 
of potential viral contaminants.  We recommend the use of a detailed flow diagram that 
includes all materials used as the usual, most effective, presentation of this information. 
 
  Quantitative composition of the product 
 
  A brief description of adequate test methods used to ensure the identity, strength, quality, 
purity, and potency accompanied by the test results, or a certificate of analysis, of the 
candidate product lots used in toxicological studies and intended for the proposed human 
study.  For biotechnology products produced in mammalian cells or animals, this will 
include tests and studies to ensure the removal and/or inactivation of potential viral 
contaminants. 
  Information that demonstrates the stability of the product during toxicology studies and 
an explanation of how stability will be evaluated during the clinical studies 
                                                 
11  Excipients considered to be generally recognized as safe (GRAS) are included in a list that is maintained on the 
Internet at http://www.accessdata.fda.gov/scripts/cder/iig/index.cfm.  See also 21 CFR 330.1, which explains the 
GRAS concept. 
 
12  Novel excipients should be appropriately qualified for their intended use.  FDA has issued guidance on 
Nonclinical Studies for Development of Pharmaceutical Excipients.   
  7 Contains Nonbinding Recommendations 
  For ophthalmic, inhalational (aqueous base), or parenteral dosage forms, results from 
sterility and pyrogenicity tests 
  
2.  Analytical characterization of candidate product 
 
There are two scenarios under which CMC information can be provided to an IND application.  
In the first scenario, the same batch of candidate product is used in both the toxicology studies 
and clinical trials.  This material will be qualified for human use based on the CMC information 
(see III.B.1, above) and results of the toxicology studies described elsewhere in this guidance.  
Although we recommend establishing the impurity profile to the extent possible for future 
reference and/or comparison, not all impurities of the candidate product may need 
characterization at this stage of product development.  If an issue arises during the toxicology 
qualification of the product, the appropriate parameters can be studied further, on an as-needed 
basis.  Impurities (e.g., chemical and microbiological) should be characterized in accordance 
with recommendations in Agency guidance,13 if, and when, the sponsor files a traditional IND 
for further clinical investigation. 
 
In the second scenario, the batch of candidate drug product to be used in the clinical studies may 
not be the same as that used in the nonclinical toxicology studies.  In such a case, the sponsor 
should demonstrate by analytical testing that the batch to be used is representative of batches 
used in the nonclinical toxicology studies.  To achieve this, relevant analytical quality test results 
should be sufficient to enable comparison of different batches of the product.  Tests to 
accomplish this include: 
 
  Identity 
  Structure (e.g., optical rotation (for chiral compounds), reducing/non-reducing 
electrophoresis (for proteins))  
  Assay for purity 
  Impurity profile (e.g., product- and process-related impurities, residual solvents, 
heavy metals)  
  Assay for potency (biologic) 
  Physical characteristics (as appropriate) 
  Microbiological characteristics (as appropriate) 
 
C.  Safety Program Designs  Examples  
 
Pharmacology and toxicology information is derived from preclinical safety testing performed in 
animals and in vitro.  Preclinical studies for small molecules are described in ICH M3 while 
those for biologics follow guidance described in ICH S6.  Some of the toxicology tests described 
in this guidance may not be appropriate for biologics.  The toxicology evaluation recommended 
for an exploratory IND application is more limited than for a traditional IND application.14  The 
                                                 
13  See footnote 10 and guidance for industry, INDs for Phase 2 and Phase 3 Studies, Chemistry, Manufacturing, 
and Controls Information. 
 
14 International Conference on Harmonisation (ICH) guidance for industry M3 Nonclinical Safety Studies for the 
Conduct of Human Clinical Trials for Pharmaceuticals describes what is expected for a traditional IND. 
  8 Contains Nonbinding Recommendations 
basis for the reduced preclinical package is the reduced scope of an exploratory IND clinical 
study.  Although exploratory IND studies in some cases are expected to induce pharmacologic 
effects, they are not designed to establish maximally tolerated doses.  Furthermore, the duration 
of drug exposure in exploratory IND studies is limited.  The level of preclinical testing 
performed to ensure safety will depend on the scope and intended goals of the clinical trials. 
 
There are a number of study objectives for which the preclinical safety programs may be tailored 
to the study design.  Examples include: confirming that an expected mechanism of action can be 
observed in humans; measuring binding affinity or localization of drug; assessing PK and 
metabolism; comparing the effect on a potential therapeutic target with other therapies.  Three 
examples are discussed in detail in the following paragraphs. 
 
1.  Clinical studies of pharmacokinetics or imaging 
 
Microdose studies are designed to evaluate pharmacokinetics or imaging of specific targets and 
are designed not to induce pharmacologic effects.  Because of this, the risk to human subjects is 
very limited, and information adequate to support the initiation of such limited human studies 
can be derived from limited nonclinical safety studies.  A microdose is defined as less than 
1/100th of the dose of a test substance calculated (based on animal data) to yield a pharmacologic 
effect of the test substance with a maximum dose of <100 micrograms (for imaging agents, the 
latter criterion applies).15  Due to differences in molecular weights as compared to synthetic 
drugs, the maximum dose for protein products is 30 nanomoles.  
 
FDA currently accepts the use of extended single-dose toxicity studies in animals to support 
single-dose studies in humans.  For microdose studies, a single mammalian species (both sexes) 
can be used if justified by in vitro metabolism data and by comparative data on in vitro 
pharmacodynamic effects.  The route of exposure in animals should be by the intended clinical 
route.  In these studies, animals should be observed for 14 days post-dosing with an interim 
necropsy, typically on day 2, and endpoints evaluated should include body weights, clinical 
signs, clinical chemistries, hematology, and histopathology (high dose and control only if no 
pathology is seen at the high dose).  The study should be designed to establish a dose inducing a 
minimal toxic effect, or alternatively, establishing a margin of safety.  To establish a margin of 
safety, the sponsor should demonstrate that a large multiple (e.g., 100X) of the proposed human 
dose does not induce adverse effects in the experimental animals.  Scaling from animals to 
humans based on body surface area can be used to select the dose for use in the clinical trial.  
Scaling based on pharmacokinetic/pharmacodynamic modeling would also be appropriate if such 
data are available. 
 
Because microdose studies involve only single exposures to microgram quantities of test 
materials and because such exposures are comparable to routine environmental exposures, 
routine genetic toxicology testing is not needed.  For similar reasons, safety pharmacology 
studies are also not recommended.  
 
                                                 
15  See European Medicines Agency (EMEA), Evaluation of Medicines for Human Use, "Position Paper on Non-
Clinical Safety Studies to Support Clinical Trials with a Single Microdose," CPMP/SWP/2599/02Rev 1, 23 June 
2004. 
  9 Contains Nonbinding Recommendations 
2.  Clinical trials to study pharmacologically relevant doses 
 
A second example involves clinical trials designed to study pharmacologic effects of candidate 
products.  More extensive preclinical safety data would be needed to support the safety of such 
studies.  However, since the goal would not include defining a maximally tolerated dose, the 
evaluation can still be less extensive than typically needed to support a traditional IND 
application.  See the flow chart in the Attachment to this document.  
 
Repeat dose clinical trials lasting up to 7 days can be supported by a 2-week repeat dose 
toxicology study in a sensitive species accompanied by toxicokinetic evaluations.  The goal of 
such a study would be to select safe starting and maximum doses for the clinical trial.  The rat is 
the usual species chosen for this purpose, but other species might be selected.  In addition to 
studies in a rodent species, additional studies in nonrodents, most often dogs, can be used to 
confirm that the rodent is an appropriately sensitive species.  If it is known that a particular 
species is most appropriate for a class of compounds, studies can be limited to that species.  This 
confirmation can be approached in a number of ways.  A lack of gender difference in the rodent 
study can serve as a basis for testing only a single sex in the second species if only a single sex 
will be studied in the clinical trial.   
 
The numbers of animals used in the confirmatory study can be fewer than normally used to attain 
statistically meaningful comparisons, but of sufficient number to rule out any toxicologically 
significant difference in sensitivity compared with rodent (e.g. four non-rodents per treatment 
group).  The confirmatory study could be a dedicated study involving repeat administrations of a 
single dose level approximating the rat NOAEL16 calculated on the basis of body surface area.  
Alternatively, the test in the second species could be incorporated as part of an exploratory, dose 
escalating study culminating in repeated doses equivalent to the rat NOAEL.  The number of 
repeat administrations at the rat NOAEL should, at a minimum, be equal to the number of 
administrations, given with the same schedule, intended clinically.  The route of administration 
should be the same as the expected clinical route, and toxicokinetic measurements should be 
used to assess exposure.  The same endpoints assessed in the rodent study should be evaluated in 
the second species.  If the data from the confirmatory study suggest that the rodent is not the 
more sensitive species, a 2-week repeated dose toxicity study should be performed in the second 
species to select doses for human trials.  This study should include measurements of body 
weight, clinical signs, clinical chemistries, hematology, and histopathology.   
 
In contrast to microdose studies, for clinical trials designed to evaluate higher or repeated doses, 
each candidate product to be tested should be evaluated for safety pharmacology.17  Evaluation 
of the central nervous and respiratory systems can be performed as part the rodent toxicology 
studies while safety pharmacology for the cardiovascular system can be assessed in the 
nonrodent species, generally the dog, and can be conducted as part of the confirmatory or dose-
escalation study. 
 
                                                 
16 No-observed-adverse-effect level (NOAEL). 
 
17  For details see the guidance for industry S7A Safety Pharmacology Studies for Human Pharmaceuticals. 
   
  10 Contains Nonbinding Recommendations 
In general, each product in this type of exploratory IND should be tested for potential 
genotoxicity unless such testing is not appropriate for the population (e.g. terminally ill patients) 
or product to be studied.  The genetic toxicology tests should include a bacterial mutation assay 
using all five tester strains with and without metabolic activation18 as well as a test for 
chromosomal damage either in vitro (cytogenetics assay or mouse lymphoma thymidine kinase 
gene mutation assay) or in vivo.  The in vivo test can be a micronucleus assay performed in 
conjunction with the repeated dose toxicity study in the rodent species.  The high dose in this 
case should be a maximally tolerated or limit dose.  
 
The results from the preclinical program can be used to select starting and maximum doses for 
the clinical trials.  The starting dose is anticipated to be no greater than 1/50 of the NOAEL from 
the 2-week toxicology study in the sensitive species on a mg/m2 basis.  The maximum clinical 
dose would be the lowest of the following: 
 
   14 of the 2-week rodent NOAEL on a mg/m2 basis 
  Up to 12 of the AUC at the NOAEL in the 2-week rodent study, or the AUC in the dog at 
the rat NOAEL, whichever is lower 
  The dose that produces a pharmacologic and/or pharmacodynamic response or at which 
target modulation is observed in the clinical trial 
  Observation of an adverse clinical response  
 
Escalation from the proposed maximal clinical dose should only be performed after consultation 
with and concurrence of the FDA.   
 
It is recognized that the studies described above are most appropriate for chemical drugs.  Other 
animal models (e.g. nonhuman primates) may be more appropriate for biologics, and some tests 
may be inappropriate (e.g. genetic toxicology testing) for proteins. 
 
3.  Clinical studies of MOAs related to efficacy 
 
A third example involves clinical studies intended to evaluate mechanisms of action (MOAs).  
To support this approach, the FDA will accept alternative, or modified, pharmacologic and 
toxicological studies to select clinical starting doses and dose escalation schemes.  For example, 
short-term, modified toxicity or safety studies in two animal species based on a dosing strategy 
to achieve a clinical pharmacodynamic endpoint can in some instances serve as the basis for 
selecting the safe clinical starting dose for a new candidate drug.  These animal studies would 
incorporate endpoints that are mechanistically based on the pharmacology of the new chemical 
entity and thought to be important to clinical effectiveness.  For example, if the degree of 
saturation of a receptor or the inhibition of an enzyme were considered possibly related to 
effectiveness, this parameter would be characterized and determined in the animal study and then 
used as an endpoint in a subsequent clinical investigation.  The dose and dosing regimen 
determined in the animal study would be extrapolated for use in the clinical investigation.  In 
some cases, a single species could be used if it were established as the most relevant species 
based on scientific evidence using the specific candidate intended for the clinical investigation. 
                                                 
18 For details see guidance for industry S2A: Guidance on Specific Aspects of Regulatory Genotoxicity Tests for 
Pharmaceuticals and S2B: Genotoxicity: A Standard Battery for Genotoxicity Testing for Pharmaceuticals. 
  11 Contains Nonbinding Recommendations 
Although the production of frank toxicity is not the primary intended goal of the nonclinical 
study, relevant informative endpoints (e.g., hematology and histopathology) selected as 
important for clinical safety evaluation should be investigated.  For example, an antibody that 
binds with a high degree of selectivity to a tumor-associated antigen could be studied in 
accordance with this third category.  The mechanism of action of antibody-based products is 
generally associated with their binding properties and the effect on functions associated with 
immunoglobulins.  Pharmacology and toxicology studies provide information about the selection 
of doses used in clinical studies through evidence of both a safe upper and potentially efficacious 
lower limit of exposure.  These doses might be consistent with target plasma levels of the drug 
based on animal models of disease.  The upper safe levels could be established in animal studies 
that show a lack of toxicity at these levels. 
 
  D.  GLP Compliance 
 
It is expected that all preclinical safety studies supporting the safety of an exploratory IND 
application will be performed in a manner consistent with good laboratory practices (GLP) (21 
CFR Part 58).  The GLP provisions apply to a broad variety of studies, test articles, and test 
systems.  Sponsors are encouraged to discuss any need for an exemption from GLP provisions 
with the FDA prior to conducting safety related studies, for example, during a pre-IND meeting.  
Sponsors must justify any nonconformance with GLP provisions (21 CFR 312.23(a)(8)(iii)).   
 
 
IV.  CONCLUSION 
 
Existing regulations allow a great deal of flexibility in the amount of data that needs to be 
submitted with any IND application, depending on the goals of an investigation, the specific 
human testing being proposed, and the expected risks.  Sponsors have not taken full advantage of 
that flexibility, and limited, early phase 1 studies, such as those described in this guidance, are 
often supported by a more extensive preclinical database than is needed for those studies alone.    
 
The common theme throughout this guidance is that, depending on the study, the preclinical 
testing programs for exploratory IND studies can be less extensive than for traditional IND 
studies.  This is because for the approaches discussed in this guidance, which involve 
administering sub-pharmacologic doses of a candidate product or products, the potential risks to 
human subjects are less than for a traditional phase 1 study.   
 
The Agency is undertaking a number of efforts to reduce the time spent in early drug 
development on products that are unlikely to succeed.  This guidance describes some exploratory 
approaches that are consistent with regulatory requirements, but that will enable sponsors to 
move ahead more efficiently with the development of promising candidate products while 
maintaining needed human subject protections. 
 
 
  12 Contains Nonbinding Recommendations 
ATTACHMENT 
 
A Preclinical Toxicology Testing Strategy for Exploratory INDs Designed To Administer 
Pharmacologically Active Doses 
Safety 
2-week toxicology  
Pharmacology  In vivo 
study in rodent 
CNS -  micronucleus
  species
Pulmonary
Establishment of NOAEL
Repeat dose toxicology  Safety 
study in nonrodent Pharmacology 
 
CV
Nonrodent more 
 
sensitive
Nonrodent 
equivalent or less 
sensitive 
Candidate  2-week tox 
excluded from  study in 
exp IND  nonrodent 
Calculation of clinical start 
dose, 1/50 of rat NOAEL 
Calculation of clinical 
stop dose (whichever is 
Observation of 
lowest)
adverse clinical 
response 
Achievement of 
Clinical equivalent of 1/2 of 
pharmacological 
Clinical equivalent  AUC in rat or the nonrodent 
effect or target 
to 1/4 rat NOAEL  AUC - whichever is lower 
modulation 
 
 
 
 
 
 
  13