Microencapsulation and dissolution properties of a neuroleptic in a biodegradable polymer, poly(d,l-lactide)

Polylactide was polymerized from dilactide under various conditions to yield polymers in the molecular weight range from 11,000 to 21,000 as determined by osmometry. Chlorpromazine was encapsulated by the polylactide polymers by using an emulsification-solvent evaporation method. Microscopic observation revealed that when drug loading was less than or equal to 18%, the drug was in the form of a solid solution in microspheres of polylactide. At higher drug loadings, crystalline drug was present. In vitro dissolution of the encapsulated drug was followed in hydroalcoholic and aqueous buffer media. Studies with the hydroalcoholic media revealed that the drug release rate decreased as microcapsule size increased. However, dissolution in the hydroalcoholic media did not reflect the effect of molecular weight or percentage loading observed in the aqueous system. Dissolution in aqueous buffer showed that t50% increased with molecular weight and that release rates-surface area increased with increasing drug loading.