Exploring Solid State Diversity and Solution Characteristics in a Fluorine-Containing Drug Riluzole

Solvent drop grinding experiments on riluzole, an organofluorine drug, with different carboxylic acids (mono and di) and pyridine derivatives, resulted in the formation of 10 different co-crystals, one polymorph of a co-crystal, and a salt. The crystal packing is primarily stabilized via strong N–H···O, O–H···N, O–H···O, and N–H···N hydrogen bonds, in addition to secondary interactions of the type C–H···F/O and S···F intermolecular contacts. The melting point of the new crystalline phases was observed to be present in the range of 90–140 °C which is closely related to the melting point (118 °C) of the original API. It was observed that the co-crystals depicted enhanced the solubility and dissolution rate in comparison to that of the free drug.