Pharmacokinetics of topical products

Pharmacokinetics is the study of changes in drug concentrations in the body with time. It is commonly considered in four main phases: absorption, distribution, metabolism and excretion. Following topical administration, drugs must first be absorbed into the skin, from where they distribute through the skin tissue. Drug metabolism may occur in the skin but once the drug reaches the systemic circulation, its fate is similar to that of systemically administered drugs. The concentrations of a drug that reach the target site from a topically administered medicine are highly dependent on the characteristics of both the drug itself and its formulation, as well as the properties of the skin to which it is applied. This article in providing an overview of the topic discusses the general principles affecting drug pharmacokinetics and in particular drug absorption from topically applied formulations