A quantitative approach to the determination of drug release from reverse-phase evaporation lipid vesicles. The influence of sodium ion-pair formation on warfarin partitioning and permeability

The influence of sodium ion-pair formation on warfarin partitioning and permeability has been investigated using reverse-phase evaporation lipid vesicles. An experimental method for the isolation of the vesicles having known amounts of encapsulated drug has been described. The partitioning of warfarin between phospholipid membrane and aqueous phase at different Na⁺ concentrations was determined in separate experiments. Thus, using a two-compartment cylinder assembly the influence of Na⁺ concentration on the release rate of the encapsulated warfarin from the vesicles could be measured quantitatively. It appears that under the present experimental conditions warfarin partitioning does depend on Na⁺ concentration whereas vesicle permeability towards warfarin does not seem to be affected.