The purpose of in vivo bioavailability studies is to determine the pharmacokinetics of a new drug molecule. Bioequivalence studies aim to find out if two molecules of interest are biologically identical in their therapeutic properties.

What are bioavailability studies?

Bioavailability studies are critical during drug design and development. Bioavailability is the rate and extent to which the active moiety or ingredient is available at the target site in the study system.

In the case of standard bioavailability studies, the rate and extent of absorption are equal to the area under the plasma or blood concentration-time curve and the maximum available concentration (Cmax) of the drug being tested.

For any molecule that is not absorbed into the vascular system, bioavailability assessment depends on the extent and rate of the availability of the active ingredient at the target site.

What are bioequivalent studies?

Two drugs are bioequivalent when they offer the same therapeutic effects. Two or more drugs are pharmaceutical equivalents when they have the same amount of active moieties. When they have identical active molecules, but do not have them in the same amount (dosage) these drugs become pharmaceutical alternatives of each other.

Typically, pharmaceutical equivalents are drugs that have similar dosage forms manufactured by different pharmaceutical companies, and pharmaceutical alternatives are drugs, which have different dosage forms.

What is the significance of bioavailability and bioequivalence studies?

In the US, a generic or pharmaceutical company can file an abbreviated new drug application (ANDA) with the Food and Drug Administration (FDA) when a brand-name drug is about to go off patent. The generic drugs can only become drug products or identical to brand-name or innovative drug products only if its active ingredients, route of administration, dosage and strength are the same as that of an NDA (approved).

Typically, bioavailability and bioequivalence studies require a crossover design that enables the comparison of absorption rate, availability, strength and administration route within each subject. The team of researchers collects pharmacokinetic data, which they use to conduct bioequivalence studies in accordance with regulations for bioequivalence pre-defined by the FDA.

How do bioavailability and bioequivalence studies help consumers?

Since the ANDA does not have to undergo extensive preclinical study, clinical trial and documentation, the potential cost of the ANDA drug products can be much lower than that of the brand-name drug, although they will have identical bioavailability. The ANDA drug and the approved NDA have to be bioequivalent for the former to gain FDA approval.

One of the most important roles of bioavailability and bioequivalence studies is to make generic alternatives available to the customers at lower (around 20% of the cost of brand-name drugs) prices. The FDA has mandated the evidence of the bioequivalence study of new drugs (ANDA). It is a surrogate for the clinical assessment of comparable drug products.