Role of stratum corneum lipid fluidity in transdermal drug flux.

Fatty acids are effective penetration enhancers for the transdermal delivery of certain co-applied drugs. In order to assess the mechanism of enhancement, spectrometric, calorimetric, and flux techniques were used to study porcine stratum corneum following treatment with a series of cis- and trans-positional isomers of octadecenoic acid. Results obtained from spectrometric and calorimetric measurements show increased lipid fluidity following treatment of the stratum corneum with the cis monoenoic acids which have the site of unsaturation centrally located. Under similar conditions, these same cis monounsaturated acids resulted in enhancement of salicyclic acid flux through porcine skin. The striking parallelism between flux and fluidity measurements suggests that transdermal drug flux may be ultimately related to stratum corneum lipid structure.