Rate control in transdermal beta-estradiol reservoir membrane systems: the role of membrane and adhesive layer.

PURPOSE: The aim of our study was to clarify the kinetic performance of a membrane controlled reservoir system (MCRS) for beta-estradiol (E2) under in vitro conditions by determination of the role of membrane and adhesive layer on E2 flux control.
METHODS: E2 and ethanol fluxes across EVA membrane or membrane coated with adhesive from saturated solutions in defined ethanol/PBS mixtures were measured in the symmetric and asymmetric configuration. Physicochemical parameters of the EVA membrane were determined.
RESULTS: The E2 flux across the 9% EVA membrane steadily increased with increasing ethanol concentrations in both configurations, due to enhanced uptake of E2 by the polymer and increasing membrane diffusivity. Permeation across the EVA membrane coated with an adhesive layer in symmetric and asymmetric configuration increased up to maximum values of 0.80+/-0.14 micrograms X cm-2 X h-1 and 0.37+/-0.02 micrograms X cm-2 X h-1, respectively, at 62.5% (v/v) ethanol. The fluxes then decreased with further increase in the volume fraction of ethanol due to a dramatically reduced permeability of the adhesive layer. For the asymmetric case, a linear dependence of E2 on the ethanol fluxes was observed.
CONCLUSIONS: The E2 flux from MCRS is strictly dependent on reservoir ethanol concentrations, whereas the adhesive layer represents the rate controlling barrier at high ethanol levels (> 70% v/v).