Hazard of Combining Allopurinol and Thiopurine

To the Editor: Regarding the Clinicopathologic Conference of January 27, 1972,¹ discussed by Dr. John J. Calabro involving a case of embryonal rhabdomyosarcoma in a 16-year-old boy, we wish to call attention to the effects of xanthine oxidase inhibitors on thiopurine metabolism. It is stated in the case record that the patient was discharged from the hospital “on a regimen of prednisone, 60 mg. allopurinol, 300 mg, 6-mercaptopurine (6-MP), 150 mg, and aspirin, 1.5 g, daily.” Two weeks later he presented with severe thrombocytopenia, a 10-point drop in hematocrit, leukopenia and severe epistaxis. In this respect, the case is similar.