Abstract
A pulverized phenacetin powder with a mass median diameter of 11μm was slightly granulated and subsequently coated to produce fine microcapsules by the Wurster process. As a membrane material, a 1 : 1 : 1 mixture of ethyl cellulose (EC), cholesterol (CH) and talc was used in the granulation, and a 1 : 1 : 0.06 mixture of EC, CH and stearyltrimethylammonium chloride in the coating. The produced microcapsules had a mass median diameter of 31μm at 60% coating level and exhibited a practically useful sustained release at 40% or more coaitng.In the granulation process, the membrane material solution was sprayed at a high rate of 14.2 ml/min upon 250g of phenacetin powder. The mass median diameter was increased to 19μm at a binder level of 3% (EC plus CH). THe granules were then dried to reduce the particle size to 14μm. This microgranulation and drying were effective for steady fluidization of the fine powder and to avoid excessive agglomeration. Coating was performed at a lower spray rate of 11.3 ml/min under a stronger agitation to avoid excessive agglomeration. During the coating proces, however, an increase in the mass median diameter by 17μm and the broadening of size distribution were unavoidable. The smallest size of paticle which could be coated with no subsequent agglomeration was estimated to be 20μm. The agglomeration of the particles smaller than 20μm which occupied 78% of the raw powder accounted for the particle growth and the broadening of size distribution.
