The prolongation of the in vitro dissolution of a soluble drug (phenethicillin potassium) by microencapsulation with ethyl cellulose

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Abstract
Microcapsules of phenethicillin potassium as a model water-soluble drug, coated with ethyl cellulose, have been prepared (core: wall ratios 1:1, 1:2 and 1:3) in which the taste has been masked, the odour almost eliminated and the release retarded. Sieve analysis showed that with decreasing core: wall ratios there was a trend towards increasing amounts of larger sized microcapsules. At constant core: wall ratios in vitro release of drug was generally greatest from the larger microcapsules. This result correlated with the surface areas of the microcapsules which became less as the asymmetry of the microcapsules diminished with decrease in microcapsule size. There was a linear relation between the amount of ethyl cellulose and the time for 60% release of drug, and the release pattern was analogous to that from insoluble porous matrices. Scanning electron micrographs showed the microcapsules to be irregularly shaped with circular surface pores, and they did not alter in shape or size during dissolution. Tableting of 1:1 core: wall ratio microcapsules significantly further retarded the dissolution.