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

The equilibrium solubility of sulfadiazine (SDZ) 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. At all temperatures, SDZ solubility increases with the increasing of the PEG 400 proportion in the mixtures. SDZ equilibrium solubility in mole fraction increased from x3 = 4.81 × 10− 6 in neat water to x3 = 1.29 × 10− 2 in neat PEG 400 at 298.15 K. 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 the transfer processes in all the mixtures evaluated.