Variable-temperature X-ray powder diffraction analysis of the crystal transformation of the pharmaceutically preferred polymorph C of mebendazole

Mebendazole is a common benzimidazole anthelmintic that is water insoluble. It is reported to exist in three different polymorphic forms in the solid state, i.e. polymorph A, B and C. Form C is the pharmaceutically preferred form because of its increased aqueous solubility. This paper deals with the use of variable-temperature X-ray powder analysis (VTXRPD) to study the transformation of Form C. Results showed that Form C was stable and transformed to the more stable polymorph A at high temperature (> 180 degrees C). This transformation is a first-order process with activation energy of 238 +/- 116 kJ/mole. Further studies showed that compression did not cause any significant changes in the crystal structure of polymorph C. (c) 2005 Elsevier B.V. All rights reserved.