Eudragit microcapsules of nifedipine and its dispersions in HPMC-MCC: Physicochemical characterization and drug release studies

Nifedipine and its solid dispersions in hydroxypropyl methyl cellulose-microcrystalline cellulose (HPMC-MCC) were microencapsulated with Eudragit RL PM by an emulsion solvent evaporation method. The microcapsules are spherical, discrete, free flowing, and covered with a continuous coating of the polymer. XRD and DTA indicated the presence of nifedipine in solution form in the solid dispersions and their microcapsules. No chemical interaction between nifedipine and excipients in the microcapsules was observed. Nifedipine as such and its microcapsules gave very slow release because of its highly crystalline nature and poor solubility. Solid dispersion in HPMC-MCC gave fast and rapid dissolution of nifedipine. When these solid dispersions were microencapsulated a slow, controlled and complete release over a period of 12 hr was observed from the resulting microcapsules. Drug release depended on the proportion of HPMC-MCC in the solid dispersion used as a core, coat:core ratio, and size of the microcapsules. Release was independent of pH and ionic strength. Drug release was governed by diffusion rate and followed first-order kinetics.