Abstract

Microcapsules ethylene vinyl acetate with nifedipine as the core were prepared by the method of emulsion solvent evaporation and studied. Microcapsules were free flowing discrete, spherical, types of multi nuclear matrix and monolithic. The efficiency of microencapsulation was of the order of 93-99 %. Differential calorimetry studies scanning and infrared spectroscopy indicates that there is no interaction between the coating, vinyl acetate and ethylene and the base nifedipine. The release rate of nifedipine from the microcapsules was very slow and depends on the coat: core ratio, the wall thickness and the size of the microcapsules. Release was controlled by diffusion mechanism and followed first order kinetics. A good linear relationship was observed between the wall thickness of the microcapsules and the drug release rate and the 50 % release time value. The amount of nifedipine release in microcapsule MC 1 (Size 20/35) was close to the required theoretical sustained release amount and also meets the official release rate specification of nifedipine sustained release tablets (United States Pharmacopoeia XXIV). Nifedipine soft capsules were quickly absorbed after administration. The absorption of nifedipine in ethylene vinyl acetate microcapsules was slower and lasts for up to 8-10 h. For ethylene vinyl acetate microcapsules, the serum nifedipine concentration was stable and maintained in a narrow range (28-43 ng/ml) for a longer period of time (1-10 h). Using ethylene vinyl acetate microcapsules, the average residence time increased from 3.34 h for soft capsules to 7.05 h. Compared with soft capsules (100 %), the relative bioavailability of ethylene vinyl acetate microcapsules was 91.5 %.