ABSTRACT
Most drugs are absorbed by passive diffusion. Drugs pass from the gastrointestinal tract into the bloodstream primarily by passive diffusion. Therefore bioavailability entails both the amount of drug entering the bloodstream and the rate at which it enters. Biopharmaceutics is the study of those factors which influence bioavailability and the subsequent use of this knowledge to optimize clinical success in the use of drug products. The relative bioavailability may be assessed for several dosage forms of the same drug without knowing the absolute bioavailable dose. Throughout the range of drug delivery systems a common trait is the control of drug release from the formulation relative to a rapidly dissolving tablet or capsule. Control of clinical response must therefore rely upon the assays for drug concentrations in plasma. Urinary data are more variable and their concentrations are subject to variable urine volumes.
