Allopurinol hypersensitivity syndrome

Allopurinol hypersensitivity syndrome, abbreviated AHS, typically develops in people who already have kidney failure. Weeks to months after starting allopurinol, the affected person develops a measles-like skin eruption or, less commonly, one of several more serious and potentially fatal severe cutaneous drug reactions, including DRESS syndrome, Stevens-Johnson syndrome, or toxic epidermal necrolysis; about 1 in 1,000 patients who take allopurinol are affected, and reported mortality rates for the syndrome range between 20 and 25 percent.