Prediction of in-vivo blood level with controlled-release dosage forms. Effect of the gastrointestinal tract time.

The process of in-vivo drug transfer is very complex in the case of oral dosage forms with controlled release. A numerical model taking all the known facts into account, including the release of the drug controlled by diffusion through the dosage form along the gastrointestinal tract, the kinetics of absorption in the blood compartment and the kinetics of elimination was constructed. Various parameters intervene in an important manner for a given drug: the size of the dosage form which is associated with the rate of release of the drug, and the dose frequency in multidosing. Some emphasis is placed upon the gastrointestinal tract time which appears to be the main and first parameter to be considered in preparing a dosage form.