Percutaneous absorption on the relevance of in vitro data

The use of in vitro preparations of human skin to study percutaneous absorption is widespread. Yet, up to the present time, little has been done to systematically validate this model and demonstrate the extent to which it mimicks in vivo absorption. In this study, the permeability of 12 organic compounds has been evaluated in excised skin and the results compared to those obtained previously by others in living man. With special emphasis being given here to duplicating in vivo conditions, it was possible to demonstrate an excellent qualitative agreement between the two methods. In all cases, the absorption pattern determined in vitro rather precisely paralleled the pattern which was obtained in vivo. Quantitative agreement between the two sets of data was less than perfect, although the in vitro method adequately distinguished compounds of low permeability from those of high permeability and ranked then in approximately the same order found in vivo. This systematic comparison of in vitro with in vivo data was clearly shown how accurately in vitro absorption studies can reflect the living state.