Enhanced transdermal delivery of estradiol in vitro using binary vehicles of isopropyl myristate and short-chain alkanols

Abstract The effect of binary vehicles of isopropyl myristate (IPM) and short-chain alkanols on the enhancement of skin permeation of estradiol (E 2 ) was studied in vitro using human epidermal membrane. The steady-state fluxes of E 2 and solvents across the skin were determined from saturated solutions of neat and binary solvents of IPM and ethanol (EtOH), n -propanol ( n -PrOH), n -octanol ( n -OcOH), or isopropanol (i-PrOH). While the neat solvents modestly increased the E 2 flux, addition of IPM to the alkanols resulted in a synergistic enhancement of the E 2 flux. Among the (1:1) binary cosolvents evaluated, i-PrOH produced the highest E 2 flux (1.1 μg/cm 2 per h), which was 35-fold greater than from water and over 15-fold greater than from the neat solvents. This combination was also the best in terms of relative compositions of the IPM/i-PrOH cosolvents. A strong correlation between E 2 and i-PrOH fluxes suggested the enhancement for both permeants. While i-PrOH traversed the skin, IPM was retained in the stratum corneum. The uptake of both IPM and E 2 in the stratum corneum was largely increased by adding i-PrOH (up to 50%) to IPM.