EFFECT OF SOME ORGANIC SOLVENTS IN SATURATION ON THE THERMODYNAMIC FUNCTIONS OF DISSOLUTION FOR NAPROXEN IN AQUEOUS MEDIA AT PHYSIOLOGICAL pH

Naproxen (NAP) is a widely used non-steroidal anti-inflammatory drug, whose physicochemical properties have not been thoroughly studied. As a contribution to the physicochemical characterization of NAP in aqueous solution, we evaluated the effect of some organic solvents in aqueous saturation on the thermodynamic functions of a NAP solution at physiological pH. Based on solubility values at different temperatures, using the equations of Gibbs and Van´t Hoff, the thermodynamic functions Gibb´s free energy, enthalpy and enthropy were determined for the solution and salvation processes of NAP in three aqueous saturated media at pH 7,4, each one of them with octanol W(ROH), isopropyl myristate W(IPM), or chloroform W(CLF). Results were compared with those obtained for NAP in pure buffer, W, previously reported. Solubility of NAP at 25º C increased in the following order: W(ROH) < W < W(IPM) ≤ W(CLF). In every system, enthalpies and enthropies of the solution of this drug were, respectively, positive and negative; on the other hand, solvation thermodynamic functions were negative in all cases. Results are discussed in terms of solute-solvent interactions