Characterization and Solid-State Transformations of the Pseudopolymorphic Forms of Sodium Naproxen

Abstract

Sodium naproxen is an antiinflammatory nonsteroidal drug used in the treatment of rheumatoid and arthritic diseases. Three pseudopolymorphic forms have been reported in the literature, along with characterizations of anhydrous and dihydrated forms. In the present work, the monohydrated form of sodium naproxen was prepared by dehydration of the dihydrated form and investigated with thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and microscopy. Characteristic properties of the monohydrated form were compared to the anhydrous and the dihydrated forms, and the transformation of higher hydrated forms to lower ones was performed in an oven or a desiccator without generating other polymorphic forms. DSC and isothermal TGA experiments determined the structural characteristics and mechanisms by which two types of water were removed from the hydrated species.