Measurement and Thermodynamic Modeling of Oxaprozin Solubility in Polymers and Mixed Solutions

Measuring and modeling the solubility of drugs in different solvent systems is helpful to guide the selection of appropriate solvents at various stages of drug formulation development. In this work, the gravimetrical method was used to determine the solubility data of oxaprozin (OXA) in different compositions of water/organic solvents (methanol and ethanol) binary mixtures within the range of 293.15 to 333.15 K. Subsequently, the differential scanning calorimetry method was used to measure the solubility of the drug in polymers (Polyethylene Glycol 6000 and Polyvinylpyrrolidone K30) at above 400 K. Then, the solubility of OXA in ultrapure water and polymer aqueous solution was acquired by UV spectrophotometry or HPLC within a temperature range of 303.15 to 323.15 K. Finally, the experimental values were compared with the calculated values from the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) to investigate the prediction accuracy of this model in different complex mixed solvent systems. The average relative deviations (ARD) were used to evaluate the model performance of PC-SAFT. Furthermore, PC-SAFT combined with solid–liquid equilibrium theory not only modeled the phase behavior between pure or mixed solvents and drugs independent of the molecular weight of the solvent but also did not require any experimental data or model parameters from the ternary system to predict the phase behavior of OXA in binary solvents. The results of this work illustrate that PC-SAFT is a beneficial model in drug development.