The equilibrium solubility of three pharmaceutical salts, namely, sodium naproxen (Na.NAP), procaine hydrochloride (PC.HCl), and lysine clonixinate (Lys.Clon), was determined in propylene glycol (PG) + water mixtures at 298.15 K. If the mole fraction concentration scale is considered, the mixtures' composition-dependence on solubility was different for these drugs. Thus, the solubility of Na.NAP increased nonlinearly from pure water to pure PG. By contrast, the solubility of PC.HCl decreased nonlinearly from pure water to pure PG. In a different way, the solubility of Lys. Clon increased from pure water to the mixture with mass fraction of PG, w(1) = 0.80, and later, it decreased to reach a lower value in pure PG. A good correlation of the solubility data was obtained by using the modified NIBS/R-K model. Otherwise, the apparent specific volumes at saturation of these drugs were also calculated in all the mixtures under study.