Solubility and solution thermodynamics of meloxicam in polyethylene glycol 400Â +Â water mixtures

The equilibrium solubility of meloxicam (MEL) in polyethylene glycol (PEG) 400 + water binary mixtures at temperatures from 298.15 K to 318.15 K was determined and the respective thermodynamic quantities of solution and mixing were calculated. MEL solubility increases with the increasing of the PEG 400 proportion in the mixtures at all temperatures. MEL equilibrium solubility in mole fraction increased from x3 = 4.24 × 10− 7 in pure water to x3 = 9.32 × 10− 3 in pure PEG 400 at 298.15 K. Activity coefficients of MEL decreased from 7260 in pure water to 0.33 in pure PEG 400 at the same temperature. Both Gibbs energy and enthalpy of dissolution were positive in all the mixtures under analysis. Otherwise, dissolution entropy is positive in mixtures with mass fractions of PEG 400 equal or lower than 0.40 but negative in all the other mixtures. Non-linear enthalpy-entropy compensation was found for this drug in these mixtures with variant positive slope in the plot of ΔsolnH° vs. ΔsolnG°. Thus, enthalpy-driving was found for transfer processes in all the mixtures evaluated.