Febuxostat is a selective xanthine oxidase inhibitor; like allopurinol it blocks the conversion of 6-mercaptopurine to its inactive metabolite. EMA and FDA list the combination as contraindicated in the febuxostat label.
Symptoms
Same as with allopurinol: pancytopenia with fever, infections and bleeding within the first weeks of therapy.
Management
Combination contraindicated. To treat hyperuricaemia in patients on azathioprine, use other classes: probenecid if renal function is preserved or pegloticase for severe gout.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.