[Code of Federal Regulations]
[Title 21, Volume 5]
[Revised as of April 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR320.27]

[Page 193-194]
 
                        TITLE 21--FOOD AND DRUGS
 
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN 
                          SERVICES (CONTINUED)
 
PART 320_BIOAVAILABILITY AND BIOEQUIVALENCE REQUIREMENTS--Table of Contents
 
      Subpart B_Procedures for Determining the Bioavailability or 
                     Bioequivalence of Drug Products
 
Sec. 320.27  Guidelines on the design of a multiple-dose in vivo 
bioavailability study.

    (a) Basic principles. (1) In selected circumstances it may be 
necessary for the test product and the reference material to be compared 
after repeated administration to determine steady-state levels of the 
active drug ingredient or therapeutic moiety in the body.
    (2) The test product and the reference material should be 
administered to subjects in the fasting or nonfasting state, depending 
upon the conditions reflected in the proposed labeling of the test 
product.
    (3) A multiple-dose study may be required to determine the 
bioavailability of a drug product in the following circumstances:
    (i) There is a difference in the rate of absorption but not in the 
extent of absorption.
    (ii) There is excessive variability in bioavailability from subject 
to subject.
    (iii) The concentration of the active drug ingredient or therapeutic 
moiety, or its metabolite(s), in the blood resulting from a single dose 
is too low for accurate determination by the analytical method.
    (iv) The drug product is an extended release dosage form.
    (b) Study design. (1) A multiple-dose study should be crossover in 
design, unless a parallel design or other design is more appropriate for 
valid scientific reasons, and should provide for a drug elimination 
period if steady-state conditions are not achieved.
    (2) A multiple-dose study is not required to be of crossover design 
if the study is to establish dose proportionality under a multiple-dose 
regimen or

[[Page 194]]

to establish the pharmacokinetic profile of a new drug product, a new 
drug delivery system, or a extended release dosage form.
    (3) If a drug elimination period is required, unless some other 
approach is more appropriate for valid scientific reasons, the drug 
elimination period should be either:
    (i) At least five times the half-life of the active drug ingredient 
or therapeutic moiety, or its active metabolite(s), measured in the 
blood or urine; or
    (ii) At least five times the half-life of decay of the acute 
pharmacological effect.
    (c) Achievement of steady-state conditions. Whenever a multiple-dose 
study is conducted, unless some other approach is more appropriate for 
valid scientific reasons, sufficient doses of the test product and 
reference material should be administered in accordance with the 
labeling to achieve steady-state conditions.
    (d) Collection of blood or urine samples. (1) Whenever comparison of 
the test product and the reference material is to be based on blood 
concentration-time curves at steady state, appropriate dosage 
administration and sampling should be carried out to document attainment 
of steady state.
    (2) Whenever comparison of the test product and the reference 
material is to be based on cumulative urinary excretion-time curves at 
steady state, appropriate dosage administration and sampling should be 
carried out to document attainment of steady state.
    (3) A more complete characterization of the blood concentration or 
urinary excretion rate during the absorption and elimination phases of a 
single dose administered at steady-state is encouraged to permit 
estimation of the total area under concentration-time curves or 
cumulative urinary excretion-time curves and to obtain pharmacokinetic 
information, e.g., half-life or blood clearance, that is essential in 
preparing adequate labeling for the drug product.
    (e) Steady-state parameters. (1) In certain instances, e.g., in a 
study involving a new drug entity, blood clearances at steady-state 
obtained in a multiple-dose study should be compared to blood clearances 
obtained in a single-dose study to support adequate dosage 
recommendations.
    (2) In a linear system, the area under the blood concentration-time 
curve during a dosing interval in a multiple-dose steady-state study is 
directly proportional to the fraction of the dose absorbed and is equal 
to the corresponding ``zero to infinity'' area under the curve for a 
single-dose study. Therefore, when steady-state conditions are achieved, 
a comparison of blood concentrations during a dosing interval may be 
used to define the fraction of the active drug ingredient or therapeutic 
moiety absorbed.
    (3) Other methods based on valid scientific reasons should be used 
to determine the bioavailability of a drug product having dose-dependent 
kinetics (non-linear system).
    (f) Measurement of an acute pharmacological effect. When comparison 
of the test product and the reference material is to be based on acute 
pharmacological effect-time curves, measurements of this effect should 
be made with sufficient frequency to demonstrate a maximum effect and a 
lack of significant difference between the test product and the 
reference material.

[42 FR 1648, Jan. 7, 1977, as amended at 67 FR 77674, Dec. 19, 2002]