Principles in the absorption, distribution and elimination of pharmaceuticals

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Abstract
The processes by which the body handles drugs and which determine the temporal profile of drug concentrations in the body can be conveniently categorized into: absorption—process of drug transport from the site of release of drug from the delivery system into the systemic blood circulation; distribution—process of reversible transport of drug molecules from the site of absorption to those tissues of the body into which the drug is able to distribute; and elimination—process of irreversible removal of drug molecules from the body. Elimination of drug from the body will occur by metabolism—chemical modification of drug, and/or excretion—physical removal of drug from the body, e.g. renal or biliary excretion. This article first discusses the composition and structure of mammalian cell membranes, as this is fundamental to understanding the relationship between a drug's physicochemical properties and its membrane transport, and as a corollary, the understanding of the processes of drug absorption, distribution and elimination. Mechanisms involved in the absorption, distribution and elimination of pharmaceuticals are then discussed through integration of mammalian physiology, biochemistry and drug physicochemical properties. Further, the effect of changes in the above processes upon drug concentration‐time profiles in the body is considered.