1 interaction related to tpmt
Allopurinol inhibits xanthine oxidase, the enzyme responsible for inactivating azathioprine's active metabolite 6-mercaptopurine. Combined use shunts more 6-MP into the active 6-thioguanine pathway, increasing azathioprine's effects 3-4 fold and producing potentially fatal myelosuppression, pancytopenia, and hepatotoxicity.