ABSTRACT
Before bioequivalence (BE) became a main part of the biopharmaceutical lexicon, the concept of bioavailability (BA) was established and has been defined in the Code of Federal Regulations (CFR) Sec 320.1 Subchapter D-Drugs for Human Use as follows, “Bioavailability is measured by assessing 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 (1)”. For drug products that are not intended to be absorbed into the bloodstream, BA may be assessed by measurements intended to reflect the rate and extent to which the active ingredient or active moiety becomes available at the site of action. This emphasis on active moiety suggests that an active metabolite as well as the parent drug may need to be considered in the determination of BA.
