Effect of additives on physical properties of fine ethyl cellulose microcapsules prepared by the Wurster process.

Abstract

Ethyl cellulose (EC) microcapsules with fine calcium carbonate cores (32-44μm) and drug layers were prepared. The effect of additives on the particle size distribution, the variation in drug content with particle size and the dissolution properties of the products were evaluated.Among eight additives used, cholesterol (CH) most restrained the release of phenacetin, a model drug, which resulted in a saving of coating material and time. For sustained release of phenacetin, only 6.25% or less coating material relative to core material was sufficient. In addition, CH remarkably reduced particle agglomeration. The mean particle size of a product 25% coated with EC : CH=2 : 1 mixture was 58μm. However, the drug content and the phenacetin release were strongly dependent on the particle size of the product. This was the result of retardation of particle recycling in the Wurster chamber due to its adhesion to the well by electrostatic charge. Stearyltrimethyl-ammonium chloride, a cationic surfactant, reduced the particle adhesion when it was added to EC-CH (2 : 1) in a 1% amount on a dry basis. As a result, the particle size distribution became sharper, and there was higher homogeneity of the physical properties. This effect was not observed with polysorbate 80, a nonionic surfactant.