Allopurinol associated hypersensitivity reactions: cutaneous and renal manifestations.

Five patients developed fever, "toxaemia", severe skin reactions and eosinophilia, three to six weeks after commencing allopurinol therapy. The presenting feature in these patients was an extensive erythema, progressing to an exfoliative dermatitis, sometimes with oral mucous membrane involvement. One patient developed toxic epidermal necrolysis. The clinical course in two patients was complicated by acute renal failure which necessitated dialysis. The clinical and laboratory features support an acute hypersensitivity mechanism in these allopurinol associated reactions, in agreement with previous studies. Patients with chronic renal failure appear particularly prone to severe, potentially fatal reactions. If these patients need allopurinol, a lower dose than would be normally required should be given.