Thermodynamic study of aceclofenac solubility, distribution and sublimation

Abstract

Equilibrium solubility of aceclofenac - a non-steroidal anti-inflammatory drug – has been measured using the shake-flask method between T = (293.15–313.15) K in four pharmaceutically important solvents: buffers (pH 2.0 and 7.4), 1-octanol and hexane. The activity coefficients at infinite dilution of the compound in each of the solvents and molar excess thermodynamic functions have been calculated. It has been established that the entropy term of the Gibbs energy makes the main contribution to the deviation from ideality in the studied drug – solvent systems. The saturated vapor pressures of aceclofenac have been measured in the temperature range T = (355.15–372.15) K, using the transpiration method and the sublimation enthalpy, at T = 298.15 K, has been found to be 102.7 kJ·mol−1. Based on the dissolution and sublimation data, the drug solvation enthalpies in the studied solvents have been obtained. The distribution coefficients of aceclofenac have been determined in the systems 1-octanol/buffer (pH 2.0 and 7.4) within the temperature range T = (293.15–313.15) K. The process of the drug distribution in the studied systems is characterized by favourable energy of transfer from the aqueous phase to the organic one and by positive values of transfer enthalpy and entropy. It has been found that the increase in the drug hydration in buffer solutions reduces the drug distribution coefficients.