Determination of percutaneous absorption by in vitro techniques

In vitro percutaneous absorption methods have become widely used for measuring the absorption of compounds that come in contact with skin. Safety evaluations of toxic chemicals frequently rely on in vitro studies for human permeation data. Animal data must be used cautiously for estimating human absorption due to differences in barrier properties of animal and human skin (1). In vitro absorption studies can also be used to measure skin metabolism if viable skin is obtained for the study and if the viability is maintained in the diffusion cells (2). The in vitro system allows for the isolation of skin so that metabolism of the organ can be distinguished from systemic metabolism. Important considerations is conducting in vitro absorption studies are discussed in the following sections.