Coating of pharmaceutical powders by fluidized bed process. III. Aqueous coating with ethyl acrylate-methyl methacrylate-2-hydroxyethyl methacrylate copolymer and the dissolution properties of the products.

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Abstract
Aqueous dispersions of ethyl acrylate (EA)-methyl methacrylate (MMA)-2-hydroxyethyl methacrylate (HEMA) copolymers were developed to produce microcapsules with a pH- independently water-insoluble membrane by the Wurster process. The dispersions were prepared by an emulsion polymerization technique. The resin dry weight content of the dispersion was 21-23% Lactose (328 .mu.m) and phenacetin were used as drug models. The mole ratios of EA, MMA and HEMA used were 12:6: X, 9:9:X and 6:12: X (X=4, 6, 8). An increase in MMA content raised the softening temperature of the membrane. HEMA affected it far less than MMA, but remarkably enhanced the release of lactose in JP XI disintegration 2nd fluid (pH 6.8). The delayed release of lactose, characterized by a lag time and subsequent rapid release, was observed mostly clearly for the microcapsules prepared with EA-MMA-HEMA (9:9:4) copolymer. When the lactose microcapsules contained phenacetin and polyvinylpyrrolidone (PVP), PVP did not affect the lag time, but remarkably enhanced the release of lactose after the lag time. Phenacetin who also released in a similar manner. From the expansion of the particles in the dissolution fluid, it was estimated that the lag time corresponded to the time needed for the membrane to be hydrated, and the subsequent rapid release resulted from the permeability change caused by hydration and the reduction in membrane thickness due to the particle expansion by taken-up water. Polyvinylpyrrolidone contained within microcapsules enhanced the water intake, which induced bursting of the membrane.

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