Guideline for Industry

Pharmacokinetics: 

Guidance for Repeated Dose

Tissue Distribution

Studies

ICH-S3B

March 1995
i

TABLE OF CONTENTS

I.INTRODUCTION1

II.CIRCUMSTANCES UNDER WHICH REPEATED DOSE TISSUE DISTRIBUTION

STUDIES SHOULD BE CONSIDERED2

III.DESIGN AND CONDUCT OF REPEATED DOSE TISSUE DISTRIBUTION

STUDIES2

IV.SUMMARY3

V.REFERENCE3
This guideline has been developed within the Expert Working Group (Safety) of 1

the International Conference on Harmonisation of Technical Requirements for

Registration of Pharmaceuticals for Human Use (ICH) and has been subject to

consultation by the regulatory parties, in accordance with the ICH process. This

document has been endorsed by the ICH Steering Committee at Step 4 of the ICH

process, October 27, 1994. At Step 4 of the process, the final draft is recommended

for adoption to the regulatory bodies of the European Union, Japan and the USA. In

the past, guidelines have generally been issued under § 10.90(b) [21 CFR 10.90(b)],

which provides for the use of guidelines to state procedures or standards of general

applicability that are not legal requirements but that are acceptable to FDA. The

agency is now in the process of revising §10.90(b). Therefore, this guideline is not

being issued under the authority of §10.90(b), and it does not create or confer any

rights, privileges or benefits for or on any person, nor does it operate to bind FDA in

any way. For additional copies of this guideline, contact the Consumer Affairs Branch

(formerly the Executive Secretariat Staff), HFD-210, Center for Drug Evaluation and

Research, 7500 Standish Place, Rockville, MD 20855, 301-594-1012. An electronic

version of this guideline is also available via Internet by connecting to the CDER file

transfer protocol (FTP) server (CDVS2.CDER.FDA.GOV).

GUIDELINE FOR INDUSTRY1

PHARMACOKINETICS:

GUIDANCE FOR REPEATED DOSE TISSUE DISTRIBUTION

STUDIES

I.INTRODUCTION

A comprehensive knowledge of the absorption, distribution, metabolism and elimination

of a compound is important for the interpretation of pharmacology and toxicology

studies. Tissue distribution studies are essential in providing information on distribution

and accumulation of the compound and/or metabolites, especially in relation to

potential sites of action; this information may be useful for designing toxicology and

pharmacology studies and for interpreting the results of these experiments.

In the European Union, United States and Japan, there has been a general agreement

on the need to conduct single dose tissue distribution studies as part of the non-clinical

program. These studies often provide sufficient information about tissue distribution.

There has been no consistent requirement for repeated dose tissue distribution

studies. However, there may be circumstances when assessments after repeated
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dosing may yield important information.

This paper provides guidance on circumstances when repeated dose tissue

distribution studies should be considered and on the conduct of such studies.

II.CIRCUMSTANCES UNDER WHICH REPEATED DOSE TISSUE

DISTRIBUTION STUDIES SHOULD BE CONSIDERED

A.When single dose tissue distribution studies suggest that the apparent half-life of the

test compound (and/or metabolites) in organs or tissues significantly exceeds the

apparent half-life of the elimination phase in plasma and is also more than twice the

dosing interval in the toxicity studies, repeated dose tissue distribution studies may be

appropriate.

B.When steady-state levels of a compound/metabolite in the circulation, determined in

repeated dose pharmacokinetic or toxicokinetic studies, are markedly higher than

those predicted from single dose kinetic studies, then repeated dose tissue distribution

studies should be considered.

C.When histopathological changes, critical for the safety evaluation of the test

substances, are observed that would not be predicted from short-term toxicity studies,

single dose tissue distribution studies and pharmacological studies, repeated dose

tissue distribution studies may aid in the interpretation of these findings. Those organs

or tissues which were the site of the lesions should be the focus of such studies.

D.When the pharmaceutical is being developed for site-specific targeted delivery,

repeated dose tissue distribution studies may be appropriate.

III.DESIGN AND CONDUCT OF REPEATED DOSE TISSUE DISTRIBUTION

STUDIES

The objectives of these studies may be achieved using radiolabelled compounds or

alternative methods of sufficient sensitivity and specificity.

Dose level(s) and species should be chosen to address the problem that led to the

consideration of the repeated dose tissue distribution study.

Information from previous pharmacokinetic and toxicokinetic studies should be used in

selecting the duration of dosing in repeated dose tissue distribution studies. One week

of dosing is normally considered to be a minimum period. A longer duration should be

selected when the blood/plasma concentration of the compound and/or its metabolites

does not reach steady state. It is normally considered unnecessary to dose for longer

than three weeks.
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Consideration should be given to measuring unchanged compound and/or metabolites

in organs and tissues in which extensive accumulation occurs or if it is believed that

such data may clarify mechanisms of organ toxicity.

IV.SUMMARY

Tissue distribution studies are an important component in the non-clinical kinetics

program. For most compounds, it is expected that single dose tissue distribution

studies with sufficient sensitivity and specificity will provide an adequate assessment of

tissue distribution and the potential for accumulation. Thus, repeated dose tissue

distribution studies should not be required uniformly for all compounds and should only

be conducted when appropriate data cannot be derived from other sources. Repeated

dose studies may be appropriate under certain circumstances based on the data from

single dose tissue distribution studies, toxicity and toxicokinetic studies. The studies

may be most appropriate for compounds which have an apparently long half-life,

incomplete elimination or unanticipated organ toxicity. The design and timing of

repeated dose tissue distribution studies should be determined on a case-by-case

basis.

V.REFERENCE

Federal Register, Vol. 60, No. 40, Wednesday, March 1, 1995, pages 11274-11275.