PREPARATION OF SUBMICRON DRUG PARTICLES IN LECITHIN-STABILIZED O/W EMULSIONS .1. MODEL STUDIES OF THE PRECIPITATION CHOLESTERYL ACETATE

Nanoparticles of a model drug, viz., cholesteryl acetate, were prepared. The cholesteryl acetate was dissolved in cyclohexane containing lecithin. The organic solution was emulsified in an aqueous solution containing a cosurfactant. A stable o/w emulsion resulted. The solvent was evaporated from the emulsion and cholesteryl acetate precipitated in the emulsion droplets. The size of the particles showed only minor variations with the cholesteryl acetate concentration in cyclohexane. Furthermore, the increase in particle size, as a result of an increased oil/water ratio was negligible. With a blend of phosphatidylcholine and sodium glycocholate as emulsifiers, particle sizes down to 25 nm were obtained. The ratio between phosphatidylcholine and sodium glycocholate appears to be critical. On increasing the ratio above 9 : 1, the suspension becomes more unstable as demonstrated by an increase in particle size during storage. The optimal conditions coincide with those given an extensively swelling lamellar liquid crystalline phase containing phosphatidylcholine and sodium glycocholate.