The in vitro permeability of skin and buccal mucosa to selected drugs and tritiated water.

The permeability of whole human skin, human dermis, whole pig skin, and canine buccal mucosa have been determined for four chemically different solutes: tritiated water, amphetamine, estradiol, and ouabain. Several new in vitro techniques for isolation, preservation, and permeability determination of these membranous tissues are described. Water permeabilities of human epidermis and dermis using these techniques agree well with published results. Human and porcine skins are very similar with respect to water permeability, while buccal mucosa is similar to dermis in its permeability characteristics to the four representative test agents. The permeability of hydrated whole skin is determined by the permeability of the epidermis, and the dermis and buccal mucosa behave as if they are water barriers exhibiting a permeability of about 30% of the diffusion through pure water, a difference that can be ascribed to the porosity and/or tortuosity of the tissue matrix.