TOPICS: Azathioprine, 6 MP, 6 mercaptopurine, immunomodulator, treat Crohn disease, rheumatoid arthritis, autoimmune disease, systemic lupus erythematosus, SLE, prevent organ transplant rejection, acute lymphoblastic leukemia, ALL, HGPRT, purine analog, purine antagonist, disrupts DNA synthesis, inhibit T-cell proliferation, XO, xanthine oxidase, deactivates 6-MP, risk of infection, GI distress, hepatitis, risk of malignancy, pancreatitis, pancytopenia, allopurinol co-administration, increase toxicities, febuxostat, xanthine oxidase inhibition