Solubility and Preferential Solvation of Pyrazinamide in Some Aqueous-Cosolvent Mixtures at 298.15 K

Equilibrium solubility of antitubercular agent pyrazinamide in mixed solvents is scarce in the literature. Thus, the mole fraction solubility of this drug in aqueous-cosolvent mixtures of 1,4-dioxane or ethanol has been determined at 298.15 K by means of flask shake and UV–Vis analysis. Solubilities were adequately correlated with the modified Nearly Ideal Binary Solvent/Redlich–Kister model. Moreover, some expressions for the local mole fraction of cosolvents and water around the pyrazinamide molecules in solution were derived on the basis of the inverse Kirkwood Buff integrals. Pyrazinamide is preferentially solvated by water in water-rich mixtures and cosolvent-rich mixtures, but preferentially solvated by cosolvent in mixtures with intermediate compositions.