Introduction

In a broad sense, disposition includes all processes and factors that are involved from the time a drug is administered to the time it is eliminated from the body, either in the unchanged form or as a biotransformation product. More specifically, the term encompasses the processes of absorption, distribution, metabolism, and excretion, which are depicted. Absorption is the process by which a test compound and its metabolites are transferred from the site of absorption to the systemic circulation. In animal disposition studies, the test compound is most commonly administered orally — either by gavage as a solid; as a liquid dosage form; or, often in rodents, as a drug-food mixture. In addition to solubility, other physicochemical factors can also influence the absorption of a drug solution in the gastrointestinal tract. These include instability as a result of digestive enzymes or low gastric pH, and drug complexation due to the presence of dietary components.