A statistical experimental approach to cosolvent formulation of a water-insoluble drug

Solubility of drugs in aqueous solutions

The results obtained previously by Ruckenstein and Shulgin [Int. J. Pharm. 258 (2003a) 193; Int. J. Pharm. 260 (2003b) 283] via the fluctuation theory of solutions regarding the solubility of drugs in binary aqueous mixed solvents were extended in the present paper to multicomponent aqueous solvents. The multicomponent mixed solvent was considered to behave as an ideal solution and the solubility of the drug was assumed small enough to satisfy the infinite dilution approximation. An expression derived for the activity coefficient of a solid solute in a multicomponent solvent was used to obtain an equation for the solubility of a drug in terms of its solubilities in two subsystems of the multicomponent solvent and their molar volumes. Ultimately the solubility can be expressed in terms of those in binary or even in individual solvents and their molar volumes. The method was applied to the solubility of tioconazole and 19-Nor-1alpha,25-dihydrovitamin D(2) in several ternary and in a quaternary aqueous mixed solvents. The predicted solubilities were compared with experimental data and good agreement was found.

Prediction of drug solubility in ternary solvent mixture

Applicability of the combined, nearly ideal, binary solvent/Redlich-Kister equation for calculating drug solubility in ternary mixtures is presented. The advantages of the proposed model are discussed and compared with a recently published equation that calculates the solute solubility in ternary solvent mixtures based on the mixture response methodology.