Deviation from linearity of drug solubility in ethanol/water mixtures.

A new empirical function that describes the deviation from linearity of solubility of a drug in an ethanol/water matrix is applied to the experimental data for 51 compounds. The proposed model is a more accurate predictor of the co-solvent solubility profile than a general third order polynomial with the same number of parameters. Both the root mean square error and average absolute error for the proposed model are significantly lower than those of existing models. The model also accurately predicts the fraction of co-solvent that gives maximum solubility (fmax).