Systematic solvate screening of trospium chloride: discovering hydrates of a long-established pharmaceutical

The ability of the antispasmodic agent trospium chloride (TCl) to form solvates was investigated by applying conventional solvate screening methods on 20 solvents. According to the solubility of TCl, different approaches were considered (slow evaporation, slurrying and anti-solvent addition). Five solvates, with the solvents methanol, acetonitrile, propionitrile, N,N-dimethylformamide, nitromethane and dihydrate, were identified and characterized by various analytical techniques. Moreover, a solvate with isopropyl alcohol and TCl sesquihydrate was prepared circumstantially outside the systematic screening. The structures of all the solvates were determined by single crystal X-ray diffraction. The reproducible forms were further characterized by powder X-ray diffraction and desolvation behaviour was observed by thermoanalytical (TGA/DSC) methods. Structural features of novel solvates and of previously described polymorphs and cocrystals of TCl were compared, presented by a tree diagram which classifies the structures according to their molecular packing.