Multiple Crystal Forms of p‑Aminosalicylic Acid: Salts, Salt Co-Crystal Hydrate, Co-Crystals, and Co-Crystal Polymorphs

Crystallization of p-aminosalicylic acid, an anti-tuberculosis drug, in the presence of pyridine derivatives as coformers led to formation of nine multicomponent solids that include salts, a salt co-crystal hydrate, co-crystals, and co-crystal polymorphs. Seven of them are new solid forms. The influence of the COOH···Nheterocycle synthon is examined in dictating the various crystal forms, the manifestation of which depends on solvent of crystallization and API-coformer composition in solution.