The preparation and evaluation of drug-containing poly(dl-lactide) microspheres formed by the solvent evaporation...

Several compounds such as caffeine, diazepam, hydrocortisone, progesterone, quinidine, quinidine hydrochloride, quinidine sulfate, and theophylline were evaluated for incorporation into poly(dl-lactide) (PLA) microspheres using the solvent evaporation technique. The process is generally limited to the entrapment of water-insoluble drugs. Adjustment of the pH of the aqueous phase to minimize drug solubility resulted in increased drug contents within the microspheres in the case of ionizable drugs. The release profile of quinidine from the microspheres was characterized by three different release phases, a lag time with no drug release, a burst effect of rapid drug release within a short period of time, and a slow release phase, respectively. The structure of the microsphere surface layer, which was a function of the pH of the aqueous phase at preparation, strongly influenced the rate and amount of drug released. Thermal analysis of quinidine-loaded microspheres revealed three thermal events, corresponding to the glass transition temperature of the polymer and to the recrystallization and melting of quinidine.