Imidazole-4-carboxylic Acid is used as a reagent in the synthesis of 6-Mercaptopurine-13C,15N2 (M225453, HCl); the isotope labelled analog of 6-Mercaptopurine (M225450) which is an immunosuppressive drug used to treat leukemia. It is also used for pediatric non-Hodgkin’s lymphoma, polycythemia vera, and psoriatic arthritis.