Can we exchange water in a hydrate structure: a case study of etoricoxib

Novel crystalline forms of etoricoxib (ETR) with pharmaceutically acceptable coformers (generally regarded as safe, GRAS), such as glutaric acid (1:1), adipic acid (2:1), suberic acid (1:1), and caprolactam, were co-crystallized. The solid forms were prepared from ETR hemihydrate form I and characterized by powder XRD, DSC, and IR, and finally confirmed by single crystal X-ray diffraction. The exchange of water with an organic acid coformer in the crystal structure is explained by lattice energy calculations.