Cocrystal polymorphs and solvates of the anti-Trypanosoma cruzi drug benznidazole with improved dissolution performance

Benznidazole, the primary drug used in Chagas' disease treatment, has known side effects, which may limit its widespread use. Its low solubility could negatively interfere in the bioavailability, even accentuating the toxic effects. Cocrystals have been extensively used to modify and optimize physicochemical properties, but, as single-component raw materials, they are susceptible to the phenomenon of polymorphism. In this work, we report a trimorphic cocrystal containing a 1:1 ratio of benznidazole and salicylic acid. The crystalline structures of three polymorphs were elucidated by single-crystal X-ray diffraction. Moreover, several isostructural solvates were also synthesized and analyzed. The same carboxylic acid-imidazole supramolecular heterosynthon is present in the four forms, but the main structural feature is an extended column based on amide-amide hydrogen bonds. On the basis of the crystalline structures, the trimorphic system was classified as conformational and packing polymorphism. Furthermore, the dissolution profiles of the stable forms were determined and showed a significant solubility improvement over the raw material.