Chapter 4 - Drug absorption and bioavailability

Abstract

Drug bioavailability is defined as the rate and extent of drug absorption. The rate and extent of drug absorption are determined by both drug physical chemical and formulation characteristics, and underlying patient factors. The latter include gastrointestinal motility, surface area, pH, and intestinal flora. In addition, concomitant ingestion of food or other drugs can also affect drug absorption. The calculation of oral bioavailability entails a comparison, either with an intravenous dose that is completely absorbed or with another oral formulation. In the former case, absolute bioavailability is calculated, in the latter case, the result is termed relative bioavailability. The stable isotope method for conducting bioavailability studies is described and the pharmacokinetic equations for calculating the rate and extent of drug absorption are derived.