Bioavailability bioequivalance study designs

Bioavailability & Bioequivalence
Studies
RAJENDRA D. MAHAJAN
M.PHARM – 2ND YEAR
PHARMACEUTICS

Essential to ensure uniformity in standards of
quality, efficacy & safety of Pharmaceutical
products.
Release of an active substance should be
known & reproducible.
Both Bioavailability & Bioequivalence
focus on release of drug substance from its
dosage form & subsequent absorption in
circulation.

Bioavailability
 Measurement of the relative amount & rate at which,
the drug from administered dosage form, reaches the
systemic circulation & becomes available at the site of
action
 Bioavailable fraction (F), refers to the fraction of
administered dose that enters the systemic circulation
 F = Bioavailable dose
Administered dose

Absolute Bioavailability
 Compares the bioavailability of the active drug in
systemic circulation following non-intravenous
administration with the same drug following
intravenous administration
 For drugs administered intravenously,
bioavailability is 100%
 Determination of the best administration route
Fab = (AUC)drug
(AUC)IV

Relative Bioavailability
 Compares the bioavailability of a
formulation (A) of a certain drug when
compared with another formulation (B) of
the same drug, usually an established
standard.
F rel = (AUC) drug
(AUC) standard

Concept of Equivalents
 Pharmaceutical equivalents
 equal amounts of the identical active drug ingredient,
(i.e. the same salt or ester of the therapeutic moiety)
 identical dosage forms
 not necessarily containing the same inactive ingredients
 Pharmaceutical alternatives
 identical therapeutic moiety, or its precursor
 not necessarily the same:
• salt or ester of the therapeutic moiety
• amount
• dosage form

 Bioequivalence
 Pharmaceutical equivalent / alternative of the test product,
 when administered at the same molar dose,
 has the rate and extent of absorption
 not statistically significantly different from that of the
reference product.
 Therapeutic equivalence
 Same active substance or therapeutic moiety
 Clinically show the same efficacy & safety profile

Study Design
 Good experimental design, enhances the power of the study
 Depends on: question to be answered, nature of reference
drug/ dosage form, benefit-risk ratio
 As far as possible, the study should be of crossover design &
suitably randomized
 Ideal design: Randomized two-period, two-sequence,Crossover
design with adequate washout period
 If the half-life is long: Parallel design
 For highly variable drugs: Replicate design

Fasting study
 Bioequivalence studies are usually evaluated by a single-
dose, two-period, two-treatment, two-sequence, open-label,
randomized crossover design comparing equal doses of the
test and reference products in fasted, adult, healthy
subjects.
 This study is required for all immediate-release and
modified-release oral dosage forms.
 Both male and female subjects may be used in the study.
 Blood sampling is performed just before (zero time) the
dose and at appropriate intervals after the dose to obtain an
adequate description of the plasma drug concentration–time
profile.

 The subjects should be in the fasting state
(overnight fast of at least 10 hours) before drug
administration and should continue to fast for up
to 4 hours after dosing.
 No other medication is normally given to the
subject for at least 1 week prior to the study.
 In some cases, a parallel design may be more
appropriate for certain drug products, containing a
drug with a very long elimination half-life.
 A replicate design may be used for a drug product
containing a drug that has high intrasubject
variability.

Crossover Designs
 Subjects who meet the inclusion and exclusion study
criteria and have given informed consent are selected at
random.
 A complete crossover design is usually employed, in
which each subject receives the test drug product and the
reference product.
 Examples of Latin-square crossover designs for a
bioequivalence study in human volunteers, comparing
three different drug formulations (A, B, C) or four
different drug formulations (A, B, C, D), are described
in and .

 The Latin-square design plans the clinical trial so that
each subject receives each drug product only once, with
adequate time between medications for the elimination
of the drug from the body ().
 In this design, each subject is his own control, and
subject-to-subject variation is reduced. Moreover,
variation due to sequence, period, and treatment
(formulation) are reduced, so that all patients do not
receive the same drug product on the same day and in
the same order.
 Possible carryover effects from any particular drug
product are minimized by changing the sequence or
order in which the drug products are given to the
subject.

 Thus, drug product B may be followed by drug product
A, D, or C ().
 After each subject receives a drug product, blood
samples are collected at appropriate time intervals so
that a valid blood drug level–time curve is obtained.
 The time intervals should be spaced so that the peak
blood concentration, the total area under the curve, and
the absorption and elimination phases of the curve may
be well described.

I.Two-Period Crossover Design
 2 formulations, even number of
subjects, randomly divided into 2
equal groups.
 First period , each member of one
group receive a single dose of the test
formulation; each member of the
other group receive the standard
formulation
 After a wash period (5 half lives), in
second period , each member of the
respective groups will receive an
alternative formulation & experiment
will be repeated.

Subjects Period 1 Period 2
1-8 T S
9-16 S T

II.Latin Square Design
 More than two formulations.
 A group of volunteers will receive formulations in the
sequence shown.
 a design for three different drug treatment groups given in a
three-period study with six different sequences.

 A design for four different drug treatment groups
given in a four-period study with sixteen different
sequences.

III.Balance Incomplete Block Design (BIBD)
 More than 3 formulations, Latin square design will not be
ethically advisable.
 Because each volunteer may require drawing of too many
blood samples.
 If each volunteer expected to receive at least two
formulation, then such a study can be carried out using
BIBD.

Bioavailability bioequivalance study designs

IV.Parallel-Group Design
 Even number of subjects in two groups.
 Each receive a different formulation.
 No washout necessary.
 For drugs with long half life.

T
TREATMENT A TRAETMENT B
1 2
3 4
5 6
7 8
9 10
11 12

Parallel Crossover
• Groups assigned different
treatments
• Each patient receives both
treatments
Shorter duration Longer duration
Larger sample size Smaller sample size
No carryover effect Carryover effect
•Doesn’t require stable
disease & similar baseline
•Requires stable disease &
similar baseline

V.Replicate Crossover-study design
 For highly variable drugs
 Allows comparisons of within-subject variances
 Reduce the number of subjects needed
 Four-period, two-sequence, two-formulation design
(recommended)
OR
 Three-sequence, three-period, single-dose, partially
replicated

Replicated Crossover Design
 Replicated crossover designs are used for the determination of
individual bioequivalence, to estimate within-subject variance
for both the Test and Reference drug products, and to provide
an estimate of the subject-by-formulation interaction variance.
Generally, a four-period, two-sequence, two-formulation
design is recommended by the FDA.
where R = reference and T = treatment.
 The same reference and the same test are each given twice to
the same subject. Other sequences are possible. In this design,
Reference-to-Reference and Test-to-Test comparisons may
also be made.
PERIOD 1 2 3 4
Group 1 T R T R
Group 2 R T R T

Multiple-Dose (Steady-State) Study
 In a few cases, a multiple-dose, steady-state,
randomized, two-treatment, two-way crossover study
comparing equal doses of the test and reference products
may be performed in adult, healthy subjects.
 For these studies, three consecutive trough
concentrations (C min) on three consecutive days should
be determined to ascertain that the subjects are at steady
state.
 The last morning dose is given to the subject after an
overnight fast, with continual fasting for at least 2 hours
following dose administration.
 Blood sampling is performed similarly to the single-dose
study.

 Statistical Evaluation
 Primary concern of bioequivalence is to limit Consumer’s &
Manufacturer’s risk
• Cmax & AUC analysed using ANOVA
• Tmax analysed by non-parametric methods
 Use natural log transformation of Cmax and AUC
• Calculate Geometric means of Cmax of Test [Cmax’t]
• Calculate Geometric means of Cmax of Reference [Cmax’r]
• Calculate Geometric Mean Ratio= [Cmax’t] / [Cmax’r]

 Calculate 90% confidence interval for this GMR for
Cmax
 Similarly calculate GMR for AUC
 To establish BE:
 The calculated 90% CI for Cmax & AUC, should fall
within range:
80-125% (Range of Bioequivalence)
 Non-parametric data 90% CI for Tmax should lie within
clinical acceptable range

References
 Leon Shargel, Susanna wu-pong, Andrew Yu. Applied
biopharmaceutics and pharmacokinetics. 6th edition, pg no-
417-421.
 D. M. Brahmankar, S.B. Jaiswal; “Biopharmaceutics &
Pharmacokinetics”; first edition, 12th reprint; Vallabh
Prakashan; 339 – 343.
 www.wikipedia.com
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Bioavailability bioequivalance study designs

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Bioavailability bioequivalance study designs