Characterization and Thermodynamic Relationship of Three Polymorphs of a Xanthine Oxidase Inhibitor, Febuxostat.Febuxostat (FXT), a xanthine oxidase inhibitor, is an interesting and unique molecule, which exhibits extensive polymorphism, with over 15 polymorphic forms reported to date.  The primary purpose of the study was to characterize the three polymorphic forms with respect to their thermodynamic quantities and establish thermodynamic relationship between them.  The polymorphs were characterized by thermal and powder X-ray diffraction methods.  Three different methods were used to calculate the transition temperatures (Ttr) and thereby their thermodynamic relationships.  Besides the relative thermodynamic aspects (free energy differences, enthalpy, entropy contributions) using different methods, the pharmaceutical implications and phase transformation aspects have also been covered.
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