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.

BioavailabilityMeasurement 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

Therapeutic Relevance

Absolute BioavailabilityCompares 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 BioavailabilityCompares 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

Pharmacokinetic Studies

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 DesignsSubjects 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.

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.

TTREATMENT 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 DesignReplicated 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 RGroup 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

ReferencesLeon 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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