Preparation of Pyrazinamide Eutectics versus Cocrystals Based on Supramolecular Synthon Variations

Cocrystallization of the antituberculosis drug pyrazinamide (PZA) with several substituted aromatic carboxylic acids as coformers was studied. The combinations were analyzed by X-ray diffraction and melting behavior to assess the formation of eutectic versus cocrystal. Benzoic acid, cinnamic acid, and N-heterocycle coformers gave eutectics, whereas the majority of their hydroxyl/methoxy substitutes formed cocrystals with PZA. X-ray crystal structures were obtained for some cocrystals, and binary phase diagrams were constructed to determine eutectic compositions. Differences in functional group position and variations in supramolecular growth were found to dictate the formation of eutectics versus cocrystals. Supramolecular synthon energy calculations on selected combinations validated the formation of eutectic versus cocrystal.