ENHANCED TRANSDERMAL DELIVERY OF ESTRADIOL IN-VITRO USING BINARY VEHICLES OF ISOPROPYL MYRISTATE AND SHORT-CHAIN ALKANOLS

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-stare 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 mu g/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.