Bioavailability means the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action.
Purpose of Bioavailability Studies
Bioavailability studies are performed for both approved active drug ingredients and therapeutic moieties not yet approved for marketing by the FDA. The drug product must meet all applicable standards of identity, strength, quality, and purity. To ensure that these standards are met, the FDA requires bioavailability/pharmacokinetic studies and, where necessary, bioequivalence studies for all drug products.
Bioequivalence studies are used to compare the bioavailability of the same drug (same salt or ester) from various drug products. Bioavailability and bioequivalence can also be considered as performance measures of the drug product in-vivo. If the drug products are bioequivalent and therapeutically equivalent (as defined above), then the clinical efficacy and the safety profile of these drug products are assumed to be similar and may be substituted for each other.
Pharmaceutically equivalent multi-source pharmaceutical products must be shown to be therapeutically equivalent to one another in order to be considered interchangeable. Several test methods are available to Therapeutic equivalence, including:
(a)Pharmacokinetic studies in humans (bioequivalence) in which the active drug substance or one or more metabolites are measured in an accessible biologic fluid such as plasma, blood or urine.
(b) Comparative pharmacodynamic studies in humans.
(c) Comparative clinical trials.
(d) In-Vitro Studies
|Pharmacokinetic studies||Pharmacodynamic studies||Comparative clinical trials||In – vitro studies|
|AUC||Mechanism of action||Target parameters||Formulations|
|Cmax||Efficacy studies||The size acceptance range||Site manufacture|
|Tmax||Therapeutic index||Statistical methods||Process of manufacture|
|t1/2||Safety studies||Safety end points||Manufacturing equipment|