Microemulsions for topical delivery of estradiol

Estradiol has been widely used for the treatment of hormonal insufficiencies. Due to its extensive first pass metabolism after oral administration, transdermal administration of estradiol in gels and emulsions has been used to improve its bioavailability, prolong activity and to optimize metabolic profile. The purpose of this study was to investigate microemulsions as delivery systems for estradiol. Various o/w microemulsions were used to deliver estradiol across human abdominal skin in vitro. Trasdermal flux of estradiol was determined using Franz-type diffusion cells and the samples were analyzed by high-performance liquid chromatography (HPLC). The permeation data showed that microemulsion formulations increased estradiol flux 200-700-fold over the control, but permeability coefficients were decreased by 5-18 times. The superior transdermal flux of estradiol was due to 1500-fold improvement in solubilization of estradiol by microemulsions. The results suggest that microemulsions are potential vehicles for improved topical delivery of estradiol.