Application Of Simplex Lattice Design For The Development Of Transdermal Gels Of Diclofenac Sodium
The present study deals with the preparation and evaluation of diclofenac sodium gels using an indigenously available synthetic gelling agent, Acrypol 940. A Simplex lattice design was employed for preparation of the gel possessing optimized characteristics. The amount of ethanol (X1), propylene glycol (X2) and polyethylene glycol 400 (X3) were chosen as the independent variables to study the combined effect of cosolvents. The % of drug permeated in 1,3,5 and 7 h (Y7) through the rat skin in phosphate buffer (pH 7.2) were selected as dependent variables. Full and refined models were derived for the prediction of the response variable Y7, Based on the results of multiple linear regression analysis and F-statistics, it is concluded that higher % of drug release can be obtained when X1, X2 and X3 are kept in an equal transformed proportion. The batch containing 33 % w/w of ethanol, 8.4 % w/w of propylene glycol and 8.4 % w/w of PEG 400 showed maximum drug release over 7 h in the in vitro dissolution test. The probable reasons for improved drug dissolution are permeation enhancing effect, altered drug affinity for the solvent and controlled viscosity of the gel. A contour plot is also presented to visualize the effect of the selected independent variables on Y7. The drug release data was well described by Korsemeyer and Peppas model. Considering the % of diclofenac sodium permeated in 1,3,5 and 7 h, an equation is also derived for the expression of dissolution profile. The application of the equation is demonstrated for predicting % drug permeated for an extra-design checkpoint. A permeation study of the best batch was also conducted on human cadaver skin. The release profiles obtained with rat skin and human cadaver skin were found to be comparable.