In vitro release of propranolol from oil/water microemuisions

Oil/water (o/w) microemulsions containing propranolol were studied. Isopropylmyristate was used as the oil, Tween 60 as a surfactant, butanol as a co-surfactant and a buffer of pH 6.5 for the continuous phase. The lipophilicity of propranolol was enhanced by formation of lipophilic ion-pairs to obtain a disperse phase that could act as a reservoir; octanoic acid was used as counter-ion. The diffusion rates of propranolol from microemulsions through a hydrophilic membrane decreased as the concentration of octanoic acid increased. The apparent permeability constant, determined at the beginning of the experiment, was 2.9 × 10^?9 cm s^?1 for propranolol alone and diminished until 3.5 × 10^?10 cm s^?1 in the presence of octanoic acid, at a concentration of 16.4 times that of propranolol.