[Life-threatening adverse effects of pharmacologic antihyperuricemic therapy]

Minor hypersensitivity reactions to allopurinol presenting as skin rash occur in approximately 2% of patients. A more severe, albeit rare, hypersensitivity reaction with fever, eosinophilia, dermatitis, renal failure, vasculitis and hepatic dysfunction carries a mortality of up to 20%. The incidence of this severe reaction can probably be reduced by adjusting the dose of allopurinol in patients with impaired renal function. Azathioprine and mercaptopurine are metabolised by xanthine oxidase, the enzyme that is inhibited by allopurinol. Concomitant administration can result in life-threatening neutropenia unless the dose of allopurinol is reduced by approximately 75%. The uricosuric agent benzbromarone has recently been withdrawn from the market because of several cases of fulminant hepatic failure with subsequent death of the patient or liver transplantation.