Increased risk of toxoplasmic encephalitis in human immunodeficiency virus - Infected patients with pyrimethamine-related rash

Although drug-induced rash is frequent in human immunodeficiency virus (HIV)-infected patients, rash due to pyrimethamine has not been described previously. In a randomized, double-blind, placebo-controlled study of pyrimethamine as primary prophylaxis for toxoplasmic encephalitis, the incidence of rash (per hundred patient-years) was 8.1 in the pyrimethamine group versus 1.5 in the placebo group (P < .0002). The 1-year incidence of toxoplasmic encephalitis after occurrence of rash was 37%, as compared with 9.6% in the pyrimethamine group without rash, with a 3.7 times higher risk for patients with pyrimethamine-induced rash (P = .001); the incidence was 13% in the placebo group. At the time of toxoplasmic encephalitis, pyrimethamine was successfully readministered to 80% of patients who discontinued it because of rash. Thus, pyrimethamine, when used for prophylaxis, does induce rash in HIV-infected patients. These patients are at higher risk for toxoplasmic encephalitis and should be carefully monitored for it.