Biopharmaceutics is a major branch of the pharmaceutical sciences concerned with the relationship between the physicochemical properties of a drug in a dosage form and the pharmacologic, toxicologic, or clinical response observed after its administration. The study of biopharmaceutics has been extended beyond that of a descriptive discipline by the development of pharmacokinetics, which concerns the study and characterization of the time course of drug absorption, distribution, metabolism, and excretion, as well as the relationship of these processes to the intensity and time course of therapeutic and adverse effects of drugs. Pharmacokinetics involves the application of mathematics and biochemistry in a physiologic and pharmacologic context. The development of clinical pharmacokinetics is the culmination and logical outcome of advances in the areas of pharmacokinetics, clinical pharmacology, analytic chemistry, biopharmaceutics, and therapeutics.