Crystal engineering approach to improve the solubility of mebendazole

An anthelmintic drug, mebendazole, shows a very low bioavailability (less than 10%) due to its poor aqueous solubility (0.035 mg/mL at 25 degrees C for form C). To improve its solubility, we combined a group of dicarboxylic acids with mebendazole via liquid-assisted grinding and reaction crystallization methods, and two salts with oxalic and maleic acids, as well as two co-crystals with malonic and glutaric acids, were obtained. These novel multi-component complexes were characterized by powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analyses and infrared spectra. The single-crystal structures of mebendazole-maleate salt, mebendazole-glutaric acid co-crystal, and mebendazole-monomethyl oxalate salt, in which one of the carboxyl groups of oxalic acid was esterified during the single-crystal growth in methanol, were determined. It was observed that mebendazole combines dicarboxylic acid/ester via a R-2(2)(8) hydrogen-bonding motif that involves a carbamyl benzimidazole and a carboxyl group, resulting in the 1:1 stoichiometry. The powder dissolution studies revealed that the apparent solubility of the complexes was significantly increased after the formation of co-crystals and salts.