Formulation optimization of diltiazem hydrochloride matrix tablets containing modified ispaghula husk using factorial design

The purpose of this study was to develop modified-release tablets of diltiazem hydrochloride using physically modified ispaghula husk as a hydrophilic matrixing agent. Ispaghula husk and water were exposed to heat in a hot air oven or microwave oven. The treated samples were evaluated for swelling and rigid gel formation. Microwave oven treated samples showed rigid gel formation and hence they were systematically studied using 3(2) factorial design using heating time and amount of water as independent variables. Diltiazem tablets were prepared using treated samples and analyzed for in vitro drug release. A polynomial equation was generated using statistically significant terms such as heating time, X-1, amount of water, X-2, and X1X2 and X-1(2) for predicting time required for 80% drug dissolution. Heating time was found to have a predominant effect in sustaining the drug release. A contour plot is presented for interpretation of the results. The tablets exhibited more axial swelling than radial swelling. The results of F-statistics revealed that the drug release pattern fit well in the Higuchi model.