What is bioequivalence and how is it predicted in generic formulations?

Predicting Bioequivalence During Generic Drug Formulation

Small variations in formulation can affect bioequivalence. However, with simultaneous dissolution-permeation testing, true absorption potential is revealed.

Generic drugs are essential for increasing access to therapies that are safe, effective, and affordable. They contain the same active pharmaceutical ingredient (API) as the brand-name reference product and must also demonstrate the same clinical efficacy and safety when administered to patients under specified conditions of use.

While a generic small-molecule drug should contain the same API as the reference product, its overall formulation does not need to be identical. Manufacturers can choose different excipients to enhance a product’s manufacturability, stability, or availability, provided those choices do not affect efficacy or safety.

This flexibility allows developers to alter the formulation. As a result, assessing how excipients affect the API’s dissolution and absorption characteristics, and ultimately whether there is in vivo bioequivalence, is essential.

The U.S. Food and Drug Administration (FDA), the European Medicines Agency (EMA), and other regulatory bodies require bioequivalence research before approving generic drugs. These studies are key for confirming the efficacy and safety of the generic formulation, facilitating approval, and supporting patient access to cost-effective treatments.

In 21 CFR 314.3(b), bioequivalence is defined as the “absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study.” ¹

The process for confirming the bioequivalence of different generic drug formulations with the reference product usually includes in vitro dissolution testing, which is especially important for poorly water-soluble APIs, before any clinical trials.

Such screening research aims to predict the in vivo bioavailability of formulations modified to enhance key drug characteristics and to identify optimized formulation options. Although human clinical trials for bioequivalence are the ultimate test, they are very costly and time-consuming to conduct, hence the need for more informative in vitro approaches.

Continue to the App Note

References and Further Reading

1. https://www.ecfr.gov/current/title-21/chapter-I/subchapter-D/ part-314/subpart-A/section-314.3