Drug Dosage Formulations

The discovery and development of a new drug can be a lengthy and expensive business (Fig. 1). The starting point is the active compound as synthesized by the medicinal chemist and screened by the pharmacologist. There then follows a series of complex tests and evaluations to produce a satisfactory formulation and sufficient data for presentation to regulatory authorities such as the Committee on the Safety of Drugs. Unfortunately, this aspect of drug research has been sadly neglected until recent years. Today, however, the formulation of new drugs is based on sound physical and chemical principles. To illustrate some of the concepts involved I will concentrate on the oral route of administration and pay particular attention to the fate of tablets and capsules after administration (Fig. 2). In formulation we can affect the absorption of the drug in two ways: (1) the rate at which the drug goes into solution (dissolution), or (2) the rate of absorption of the drug across biological membranes.