bioavailabilitydetermine

Bioavailability determination, in pharmacology and pharmaceutical science, is the process of assessing the extent and rate at which an administered substance enters systemic circulation and becomes available at the site of action. The two commonly used concepts are absolute bioavailability, the fraction of an administered dose that reaches systemic circulation compared to an intravenous reference dose, and relative bioavailability, the comparison between two non-intravenous formulations.

In vivo methods involve pharmacokinetic studies in humans or animals, with blood sampling to derive concentration–time profiles. The total exposure is summarized by the area under the concentration–time curve (AUC); other key metrics include maximum concentration (Cmax) and time to reach it (Tmax). Absolute bioavailability is calculated by comparing oral (or other non-intravenous) AUC to intravenous AUC, adjusting for dose. Relative bioavailability compares two formulations using the same route. Non-compartmental analysis is frequently used, though compartmental models provide detailed parameters. In vitro methods, such as dissolution testing and cell-based absorption assays, can anticipate in vivo performance and support in vitro–in vivo correlation (IVIVC).

Bioavailability is influenced by formulation, physicochemical properties, and physiological factors such as gastric pH, gut motility, enzymatic activity, and first-pass metabolism. Accurate determination supports drug development, formulation optimization, and regulatory submissions, including bioequivalence studies for generics. While gold-standard in humans is informative but costly and ethically sensitive, alternative approaches and modeling aim to predict human bioavailability from preclinical data, though with limitations. The concept also applies to nutrients, supplements, and environmental chemicals where systemic exposure is of interest.