Mathematical modeling of pH-surfactant-mediated solubilization of nimesulide.

AIM: The equilibrium-based mathematical model was used to describe the pH-surfactant-mediated solubilization of weakly acidic electrolyte, nimesulide, in buffer solutions. This model assumed that the total drug solubility could be expressed as a sum of the solubilities of four different species: unionized and ionized form in solution and their corresponding micellar forms. Sucrose-laurate, new synthetic surfactant, and polysorbate 80 were investigated for their benefits in the testing of poorly soluble acidic model drug. METHOD: Two sets of solubility data, determined at pH values 4.5 and 9.0 in media containing different surfactant concentrations, were used to calculate solubilization slopes and corresponding micellar equilibrium constants for the unionized (Kn) and ionized (K(i)) drug. These values were used to estimate drug solubilization in media considered to represent physiologically relevant conditions. RESULTS: Predicted solubility values were in good agreement with the experimental data, suggesting that the impact of pH and surfactant on nimesulide solubility could be well characterized by the equilibrium model described in this article. CONCLUSIONS: Obtained results indicated that the extent of solubilization was significantly dependent on the surfactant used.