Optimization and formulation design of carbopol loaded Piroxicam gel using novel penetration enhancers

The aim of the study was to develop and optimize Piroxicam transdermal gel formulation using three-factor, three-level Box–Behnken design by deriving a second-order polynomial equation to construct contour plots for prediction of responses as three selected independent variables with ratio of carbopol 974 (X1), ratio of propylene glycol (PG) (X2) and ratio of ethanol (X3). The dependent variables studied were the skin permeation rate of piroxicam (Y1), viscosity of the gel (Y2) and pH of the gel (Y3). Response surface plots were drawn, statistical validity of the polynomials was established to find the compositions of optimized formulation which was evaluated using the vertical Franz-type diffusion cell. The permeation rate of piroxicam increased proportionally with ethanol concentration but decreased with polymer concentration. The design demonstrated the role of the derived polynomial equation and contour plots in predicting the values of dependent variables for the preparation and optimization of gel formulation.