Formulation design and optimization of modified-release microspheres of diclofenac sodium

The present study deals with the preparation of microspheres of diclofenac sodium using cross-linked poly(vinyl alcohol) (PVA). A central composite design consisting of a two-level full factorial design superimposed on a star design was employed for developing the microspheres. The PVA to the drug ratio X1 and amount of glutaral-dehyde cross-linking agent X2 were chosen as the independent variables. The time required for 50% drug dissolution t50 in phosphate buffer (pH 7.2) was selected as the dependent variable. An optimum polynomial equation was generated for the prediction of the response variable t50. Based on the results of multiple linear regression analysis and F statistics, it may be concluded that sustained action can be obtained when X1 and X2 are kept at high levels. The X1X2 interaction was found to be statistically significant. A response surface plot is presented to show the effects of X1 and X2 on t50. The drug release pattern fit the Higuchi model well. A model was validated for accurate prediction of the drug dissolution profile with constraints on the percentage drug release in the first, fifth, and seventh hours. The data of a selected batch were subjected to an optimization study, and an optimal formulation was fabricated. Good agreement was observed between the predicted and the observed dissolution profiles of the optimal formulation.