Application of Carbopol^® to Controlled Release Preparations. II. Controlled Release by Use of Carbopol^® as a Matrix Material, as a Coating Material, and as Both

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The release properties of theophylline (TP) from three different types of tablets were investigated, one using a carboxyvinylpolymer (Carbopol^®: CP) as a matrix material and/or as a coating material. CP-matrix tablets were prepared from TP, lactose, and CP by the direct compression method. CP-coated tablets were prepared by spraying an aqueous solution or dispersion of CP onto core tablets containing TP. CP-coated matrix tablets (CM tablets) were prepared by spraying CP aqueous dispersion onto CP-matrix tablets. TP release profiles from each type of the tablet were studied by the JP 13 paddle method, using JP 1st fluid (pH 1.2), purified water, and JP 2nd fluid (pH 6.8) as the dissolution media. The swelling behaviors of the tablets in each of the dissolution media were observed. When CP was used as a matrix material, TP release was retarded in the JP 2nd fluid. On the other hand, when CP was used as a coating material, the release was slowed in both JP 1st fluid and purified water. TP release from the CP-matrix tablet and CP-coated tablet varied depending on the addition amount and the grade of CP. When CP was used in the combination, TP release was retarded in all dissolution media. Furthermore the difference in TP release, depending on the dissolution medium, was decreased. These results suggest that it is feasible to control drug release in various pH environments by using CP as a matrix material, coating material, or both and by varying the addition amount and the grade of CP.