The Importance Of Bioavailability Assay In Creating Generic Drugs

Bioavailability assays measure the extent and rate to which a drug is absorbed and becomes available at the site of drug action. Bioavailability is of two types, absolute and relative bioavailability. However, relative bioavailability is considered to predict clinical outcomes and thus becomes the primary evaluation step in drug development. Bioavailability and bioequivalence (BA/BE) studies are vital in clinical research. Bioequivalence studies for generic drugs form a crucial step in the drug development of generic products.

In 1984, the US FDA became the authorized party to approve generic drug products. The US FDA approves generic drugs based on in vivo bioequivalence data. Hence, bioequivalence CRO focuses on in vivo bioequivalence studies to gain permission from the FDA. The current article focuses on the importance of bioavailability assay in BABE studies for creating generic drug products.

Significance of Bioavailability assays

The rate and extent of drug absorption are generally determined by defining AUC and Cmax values. However, for drug products not absorbed into the bloodstream, researchers may determine bioavailability by estimating the intended rate and extent of drug absorption and its availability at the site of action. Researchers often perform comparative bioavailability studies to differentiate the bioavailability of different drug products or different formulations of the same drug.

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When two drug products or two formulations of the same drug are bioequivalent, that means they offer the same therapeutic effect or are therapeutically equivalent. However, these two terms are not interchangeable. Two drug products are pharmaceutical equivalents if they have the same amount of the identical active ingredient. On the other hand, two drug products are pharmaceutical alternatives if they have identical therapeutic moiety but not necessarily the same dosage form or amount or ester.

Two drugs are considered bioequivalent if they are pharmaceutical alternatives or pharmaceutical equivalents and their extent and rate of absorption do not vary significantly, or their availability at the site of action does not differ significantly when administered at the same doses and similar conditions.

When a brand-name drug is on the verge of going off-patent, companies may file an ANDA application for generic approval. Generic drug products are identical to innovative drug products. The US FDA monitors the active ingredients, dosage form, route of administration, condition of use, and strength.

As ANDA studies do not require lengthy clinical studies, generic drugs are generally available at much lower costs than their brand-name counterpart. The purpose of generic drugs is to make medicines safe, less expensive, and equally effective for the general public. For the approval of a generic pharmaceutical drug, the US FDA needs data demonstrating therapeutic equivalence between a generic and a brand-name drug through bioequivalence and bioavailability studies.

A typical bioequivalence study involves healthy male volunteers. It demonstrates the efficacy of the relative bioavailability of a drug to predict clinical outcomes. A bioequivalence study generally employs a crossover design for comparing study subjects. Researchers collect pharmacokinetic data and assess bioequivalence using statistical methods with pre-specified criteria. Once the US FDA is satisfied with the data, the generic drug can substitute the brand-name drug.