Optimization of drug release from dermatological semisolid preparations

The aim of the present study was to optimize the process of drug release. Factors which influence drug release were studied in detail and their effects were described numerically. The factors studied were as follows: the concentration of the pharmacon (salicylic acid); its particle size; its suspended, dissolved, solubilized, or molecular encapsulated state;, the composition of the vehicle; the quantities of the polar and apolar components; and the viscosity of the vehicle. Drug release studies were carried out with Hanson's vertical diffusion cell. The process was described quantitatively by the slope of the equation describing the time‐course of the liberation, by the quantity of pharmacon liberated in 8 h and also by the optimization parameter determined on the basis of the 22 model of the factorial design method. Increase of the concentration of salicylic acid was found to be accompanied by an exponential rise in drug release, while the extent of liberation decreased linearly with increasing viscosity. The greatest increase in the optimization parameter was observed when the polarity of the vehicle was changed. The process of liberation consists of the following steps: dissolution of the pharmacon, diffusion of the dissolved molecules, and their distribution. The current data revealed that the distribution is the most important element and exerts the greatest influence on optimal drug release. Drug Dev. Res. 59:316–325, 2003.