Table 1 Major limitations of allopurinol therapy

Rash in about 2% of treated patients

Additional intolerance in up to 10% of patients (includes hepatic enzyme, gastrointestinal, and central nervous system effects)

Allopurinol hypersensitivity syndrome: <1/1000 treated patients, but 20% fatality rate

Prolonged renal elimination of active oxypurinol metabolite necessitates reduced dose in renal disease with impaired function

Contraindicated in patients receiving azathioprine or 6-mercaptopurine