Design and optimization of diclofenac sodium controlled release solid dispersions by response surface methodology.

A 3(2) factorial design was employed to produce controlled release solid dispersions of diclofenac sodium in Eudragit RS and RL by coevaporation of their ethanol solution in a flash evaporator. The effect of critical formulation variables namely total polymer pay loads and levels of Eudragit RL on percent drug incorporation (% DI), drug release at the end of 12 hours (Rel(12)) and drug release at the end of 3 hours (Rel(3)) were analyzed using response surface methodology. The parameters were evaluated using the F test and mathematical models containing only the significant terms were generated for each parameter using multiple linear regression analysis and analysis of variance. Both the formulation variables studied exerted a significant influence (p < 0.05) on the drug release whereas the total polymer levels emerged as a lone factor significantly influencing the percent drug incorporation. Numerical optimization technique employing desirability approach was used to develop a new formulation by setting constraints on the dependent and independent variables. The experimental values of % DI, Rel(12) and Rel(3) for the optimized batch were found to be 95.22 +/- 1.13%, 74.52 +/- 3.16% and 29.37 +/- 1.26% respectively which were in close agreement with those predicted by the mathematical models. The Fourier transform infrared spectroscopy, Differential scanning calorimetry and Powder x-ray diffractometry confirmed that the drug was reduced to molecular or microcrystalline form in the hydrophobic polymeric matrices, which could be responsible for the controlled drug release from the solid dispersions. The drug release from the solid dispersions followed first order rate kinetics and was characterized by Higuchian diffusion model.