Dermal penetration enhancement profile of hexamethylenelauramide and its homologues: in vitro versus in vivo behavior of enhancers in the penetration of hydrocortisone.

Several amides of cyclic amines were prepared and tested as penetration enhancers in the diffusion of various drugs through hairless mouse skin in vitro. Hexamethylenelauramide (hexahydro-1-lauroyl-1H-azepine) was selected as a broad spectrum penetration enhancer worthy of further study. Later, the duration of the effect of various enhancers on the penetration barrier in vivo was determined by evaluating the in vitro diffusion of hydrocortisone through skins that had been pretreated in vivo. We found that the longer the pretreatment, the smaller the amount of penetrated hydrocortisone. Furthermore, our results suggested that differences exist in the retention of various enhancers in living mouse skin. The in vitro pretreatment experiments revealed that the penetration through dead skin is slow compared with the penetration through living skin. Neither the nature of the receptor phase, nor the increased temperature of the in vitro experiments, explain the striking differences between the in vivo and the in vitro experiments. Finally, the penetration of hydrocortisone through the stratum corneum in the presence of enhancers, as well as the penetration of 1-dodecylhexahydro-2H-azepin-2-one (laurocapram), hexamethylenelauramide, and oleic acid, were determined using a stratum corneum stripping technique. More hydrocortisone penetrated through the stratum corneum during the first 3 h in the presence of hexamethylenelauramide than in the presence of laurocapram or oleic acid.