Polymorphism of Tegafur: Physico-chemical Properties of Four Polymorphs.

Four crystalline forms of tegafur were prepared by recrystallization from different solvents (α-, β-, δ-forms) and by heating (γ-form). They have been characterized using powder X-ray diffraction, thermal analysis, microscopy, density measurements and infrared spectroscopy. From differential scanning calorimetry measurements, it was confirmed that the γ- and δ-forms melted at 175°C and 165°C, whereas the α- and β-forms transformed into the γ-form at about 162°C and 120°C, respectively. The infrared absorption spectral differences observed between the α- and β-forms were discussed in relation to their intermolecular hydrogen bonding systems. It was also found that the difference in crystal forms significantly altered the dissolution rate of tegafur.