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Bioequivalence Studies for Solid Oral Drug Products

Objective of Bioequivalence Studies

The objective of a bioequivalence study is to measure and compare formulation performance between two or more pharmaceutically equivalent drug products.

Design of Bioequivalence Studies

The FDA’s Division of Bioequivalence, Office of Generic Drugs provides guidance for the performance of in vitro dissolution and in vivo bioequivalence studies. These guidance are available at their official website.

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 (generic) and reference (brand) products in fasted, adult, healthy subjects.

  • Both men and women may be used in the study.
  • Blood sampling is performed just before the dose (zero time) and at appropriate intervals after the dose to obtain an adequate description of the plasma drug concentration versus time profile.

Food Intervention Study

If the bioavailability of the active drug ingredient is known to be affected by food, the generic drug manufacturer must include a single-dose, randomized, crossover, food effects study comparing equal doses of the test product and reference products given immediately after a standard high fat content breakfast.

Other Study Designs

Crossover studies may not be practical in drugs with a long half-life in the body, and a parallel study design may be used instead. Alternate study methods, such as in vitro studies or equivalence studies with clinical or pharmacodynamic end points, are used for drug products where plasma concentrations are not useful to determine delivery of the drug substance to the site of activity (such as inhalers, nasal sprays, and topical products applied to the skin).

Waiver of an In-vivo Bioequivalence Study (Biowaiver)

  • A comparative in vitro dissolution (drug-release) study between the test and the reference products may be used in lieu of an in vivo bioequivalence study for some immediate-release (conventional) oral drug products.
  • No bioequivalence study is required for certain drug products given as a solution such as oral, parenteral, ophthalmic, or other solutions because bioequivalence is self-evident. In this case, the drug is in a pure aqueous solution, and there is no drug dissolution rate consideration.
  • Immediate-release (IR) solid oral drug products that meet biopharmaceutics classification system (BCS) class 1 drugs—that is, highly water soluble, rapidly dissolving, and rapid permeation of cellular membranes—may obtain a biowaiver.
  • Drug products containing a lower dose strength (e.g., 200 mg, 100 mg, and 50 mg IR tablets). The drug product must be in the same dosage form, lower strength, and is proportionately similar in its active and inactive ingredients.

Pharmacokinetic Evaluation of the Data

Pharmacokinetic analysis includes calculation for each subject of the AUC to the last quantifiable concentration (AUC 0-t) and to infinity (AUC 0-∞), Tmax, and Cmax. In addition, the elimination rate constant (k), the elimination half-life (t½), and other parameters may be estimated.

Statistical Evaluation of the Data

The statistical methodology for analyzing bioequivalence studies is called the two one-sided test procedures. Two situations are tested with this statistical methodology.

  • The first of the two one-sided tests determines whether a generic product (test), when substituted for a brand-name product (reference), is significantly less bioavailable.
  • The second of the two one-sided tests determines whether a brand-name product (reference), when substituted for a generic product (test), is significantly less bioavailable.

Based on the opinions of FDA medical experts, a difference of > 20% for each of the aforementioned tests was determined to be significant and, therefore, undesirable for all drug products.

An analysis of variance (ANOVA) should be performed on the log transformed AUC and Cmax values obtained from each subject. The 90% confidence intervals for both pharmacokinetic parameters, AUC and Cmax, must be entirely within the 80% to 125% boundaries based on log transformation of the data. 

The ratio of the means of the study data (test to reference) should lie in the center of the 90% confidence interval, or close to 100% (equivalent to a test to reference ratio of 1).

Different statistical criteria are sometimes used when bioequivalence is demonstrated through comparative clinical trials, pharmacodynamic studies, or comparative in vitro methodology.

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