Microencapsulation of paracetamol using polyacrylate resins (Eudragit Retard), kinetics of drug release and evaluation of kinetic model.

Methacrylate copolymers were used for microencapsulation of paracetamol by phase separation from chloroform with polyisobutylene 6% in cyclohexane. With polyisobutylene as an anti-aggregating agent, high quality microcapsules were obtained. Drug release appeared to fit both first order and Higuchi matrix model kinetics. However, on application of the differential rate treatment, the evidence supported the first order description, which was further supported by computed simulations of the models. Variation of production conditions showed that increasing the proportion of core material raised the microcapsule drug content and the release rate. Reduction of core particle size correlated with reduced coating thickness and faster release rate. The rate constants correlated with the estimated surface areas and wall thicknesses of the various batches. The data were used to estimate an apparent permeability constant for paracetamol in Eudragit RS microcapsules, which was constant and comparable with values found single core, non-aggregated microcapsules containing other similar drugs and different wall materials.