VEHICULAR INFLUENCE ON TRANSDERMAL DRUG PENETRATION

The realization of the composition and structure of the intercellular multiple bilayers of the horny layer lipids has created a basis for understanding the diffusive control of transdermal xenobiotic permeation and the enhancing effects of vehicles and other ingredients added to dermal preparations. The measurement of concentration profiles in the stratum corneum and deeper skin layers yields insight into the transdermal permeation mechanisms. Lipid solubility is a predominant criterion for the transdermal permeation of substances which enter via the lipid route. Applying lipid vehicles, liquid components carrying dissolved drug substances enter the intercellular spaces of the stratum corneum disjunctum by spreading and by capillary action. Drugs and certain vehicle constituents diffuse into the stratum corneum conjunctum and deeper skin layers. There, they lower the diffusion resistance of the horny layer by interfering with the molecular packing of the dermal lipids and by disturbing their order. Furthermore, the dissolving power of the horny layer lipids may be changed.