Data monitoring experience in the AIDS toxoplasmic encephalitis study

The toxoplasmic encephalitis (TOXO) study was designed to determine whether primary prophylaxis with pyrimethamine (25 mg thrice weekly) or clinidamycin (300 mg twice daily) would reduce the incidence of toxoplasmic encephalitis (TE) among HIV-infected patients considered at risk for the opportunistic infection. Using a modified double-blind design, patients were randomized to clindamycin or matching placbo (2: 1) or to pyrimethamine or matching placebo (2: 1). The clindamycin arm of the study was terminated after a median follow-up of three months due to dose-limiting toxcities; the pyrimethamine arm was terminated after a median follow-up of eight months due to a very low TE event rate in the placebo and pyrimethamine groups and a higher death rate among patients assigned pyrimethamine.