שאלה משלב א׳ במחלות עור ומין · מועד 2021, שאלה 141

The drug added is ALLOPURINOL, which blocks xanthine oxidase and so prevents the degradation of 6-mercaptopurine, causing a massive rise in azathioprine's active metabolites with profound MYELOSUPPRESSION - presenting here as thrombocytopenia and bleeding. If the combination is unavoidable the azathioprine dose must be cut to about a quarter with close blood count monitoring (febuxostat carries the same interaction); the other interactions to remember are with ACE inhibitors, co-trimethoprim and warfarin, and TPMT/NUDT15 activity should be checked before starting azathioprine.

מקור: Bolognia p. 2300