Physico-chemical properties and bioavailability of benoxaprofen polymorphs.

The different crystal forms of benoxaprofen were obtained by recrystallization from several solvents. These crystal forms were identified by using X-ray diffractometry, infrared spectroscopy, differential scanning calorimetry and thermogravimetry. It was found that benoxaprofen exists in two polymorphic forms and that form II is more stable than form I. The thermodynamic values of the two polymorphic forms of benoxaprofen were calculated from solubility measurements. The transition temperature and the free energy difference (ΔG) were estimated to be 98.0°C and-232cal/mol, respectively. The solubility of form I was about 1.5 times greater than that of form II. However, there was no significant difference in the bioavailability of the two polymorphic forms in rabbits.