Release of drugs from oil-water microemulsions

The release of five drugs with different lipophilicities from oil-water (o/w) microemulsions (isopropyl myristate as oil, 1-butanol as cosurfactant, aerosol-OT as surfactant and buffer, pH 7.0, as the aqueous phase) was studied by determining mass transfer constants of the drugs through a hydrophilic membrane separating the o/w microemulsions from the receiving aqueous phase. The initial mass transfer constants measured were linearly related to the partition coefficients (P_cos) of the drugs in the oil-cosurfactant-water mixtures. The P_cos values were used to approximate the drug concentration in the aqueous phase of the emulsion. The initial mass transfer constants of different drugs calculated on the basis of these concentrations were very similar to the mass transfer constants of the drugs obtained by permeation studies through the same membrane using an aqueous phase.