Two new solvates of the widely used anthelminthic Praziquantel (PZQ) were obtained
through mechanochemical screening with different liquid additives. Specifically, 2-pyrrolidone and
acetic acid gave solvates with 1:1 stoichiometry (PZQ-AA and PZQ-2P, respectively). A wideranging characterization of the new solid forms was carried out by means of powder X-ray
diffraction, differential scanning calorimetry, FT-IR, solid-state NMR and biopharmaceutical
analyses (solubility and intrinsic dissolution studies). Besides, the crystal structures of the two new
solvates were solved from their Synchrotron-PXRD pattern: the solvates are isostructural, with
equivalent triclinic packing. In both structures acetic acid and 2-pyrrolidone showed a strong
interaction with the PZQ molecule via hydrogen bond. Even though previous studies have shown
that PZQ is conformationally flexible, the same syn conformation as the PZQ Form A of the C=O
groups of the piperazinone-cyclohexylcarbonyl segment is involved in these two new solid forms.
In terms of biopharmaceutical properties, PZQ-AA and PZQ-2P exhibited water solubility and
intrinsic dissolution rate much greater than those of anhydrous Form A.
