Lesson of the Week: Allopurinol, erythema multiforme, and renal insufficiency

Allopurinol, a xanthine oxidase inhibitor, has become established as the drug of choice for preventing and treating conditions where there is overproduction of uric acid, such as occurs in gout, uric acid nephro- lithiasis, and polycythaemia vera; during chemotherapy for lymphomas; and in the Lesch-Nyhan syndrome.'Allopurinol may, however, cause a severe, and sometimes fatal, hypersensitivity reaction in patients with pre-existing renal disease.We describe two patients with severe hypersensitivity.In both the syndrome was relapsing and in one ultimately fatal.