ESTRADIOL PERMEATION FROM NONIONIC SURFACTANT VESICLES THROUGH HUMAN STRATUM-CORNEUM IN-VITRO

The permeation of estradiol from vesicular formulations through human stratum corneum was studied in vitro. The vesicles were composed of no nionic n-alkyl polyoxyethylene ether surfactants (C(n)EO(m)). The ther modynamic activity of estradiol present in each formulation was kept c onstant by saturating all formulations with estradiol. The effects of both the particle size and the composition of the formulation on estra diol permeation across excised human stratum corneum were investigated . Stratum corneum that was pretreated with empty surfactant carriers a llowed for significantly higher estradiol fluxes compared with untreat ed stratum corneum. However, estradiol fluxes obtained in these pretre atment experiments appeared to be significantly lower than those obtai ned by the direct application of the estradiol-saturated carrier formu lation on top of the stratum corneum. Furthermore, in the case of pret reatment of the stratum corneum, an increase in carrier size resulted in a decrease in estradiol flux. For direct application the opposite w as found. Two mechanisms are proposed to play an important role in ves icle-skin interactions, i.e., the penetration enhancing effect of surf actant molecules and the effect of the vesicular structures that are m ost likely caused by adsorption of the vesicles at the stratum corneum -suspension interface.