Gastrointestinal and dermal absorption: interspecies differences

It has been repeatedly demonstrated that there are considerable interspecies differences with respect to the dermal absorptions of a chemically diverse set of substances, ranging from ionic substances to complex organic molecules, some of which are of great relevance to environmental/occupational health (e.g., the organophosphate insecticides). In general, human skin was found to be much less permeable to the substances evaluated when compared to rabbit and rodent skin; however, the pig and monkey appear to most closely simulate the absorption capabilities of human skin for a variety of substances. Unfortunately, no truly systematic evaluations of numerous classes of compounds have been made via interspecies comparisons. Thus, even though the data derived until now are very consistent, one could argue that strong general conclusions with respect to interspecies differences in dermal absorption cannot yet be made because the substances evaluated thus far may not be sufficiently representative. Clearly, further research along these lines is required.