Table 3.

6-Mercaptopurine (6-MP) Drug Interactions

Drug	Drug-Drug Interaction	Renal Impairment	Hepatic Impairment
6-MP	Allopurinol: may cause increased levels of mercaptopurine by inhibition of xanthine oxidase; may potentiate effect of bone marrow suppression. Aminosalicylates (olsalazine, mesalamine, sulfasalazine): may inhibit thiopurine methyltransferase, increasing toxicity and causing leukopenia/myelosuppression Azathioprine: metabolized to mercaptopurine; concomitant use may result in profound myelosuppression Doxorubicin: synergistic liver toxicity with mercaptopurine in more than 50% of patients Hepatotoxic drugs: any agent that could potentially alter the metabolic function of the liver could produce higher drug levels and greater toxicities from either mercaptopurine or 6-thioguanine Warfarin: mercaptopurine inhibits the anticoagulation effect of warfarin by an unknown mechanism	Dose should be reduced to avoid accumulation, but specific guidelines are not available Hemodialysis removed; supplemental dosing is usually required	Dose should be reduced to avoid accumulation, but specific guidelines are not available

5-ASA

5-aminosalicylic acid.