A Randomized Prospective Study of Pyrimethamine Therapy for Prevention of Toxoplasmic Encephalitis in HIV-Infected Individuals With Serologic Evidence of Latent Toxoplasma Gondii Infection

Inclusion Criteria Concurrent Medication: Required: * Prophylactic treatment for Pneumocystis carinii pneumonia with aerosolized pentamidine, dapsone, or trimethoprim / sulfamethoxazole. Allowed: * Most medications not specifically excluded. Prior Medication: Allowed: * Antivirals. * Antiretrovirals. Patients: * Must be HIV positive or have an AIDS-defining illness OR be at known risk for HIV infection and have a CD4 cell count \< 200/mm3 and no other known immunosuppressive disease. * Must have positive titer for Toxoplasma gondii. * Must be or become a patient of a CPCRA physician. * May participate in other clinical trials as long as there is no potential activity against Toxoplasma gondii or cross-toxicity among study drugs. Exclusion Criteria Co-existing Condition: Patients with the following conditions or symptoms are excluded: * History of ocular, pulmonary, or central nervous system (CNS) toxicity. * CNS lesions. * Neurologic deficits except peripheral neuropathy. * Mild, moderate, severe, or end-stage AIDS dementia complex. Grade 3 or higher nausea and/or vomiting. * Sensitivity to pyrimethamine. Concurrent Medication: Excluded: * On-going therapy with clindamycin, fansidar, methotrexate, trimetrexate, spiramycin, azithromycin, clarithromycin, 566C80, and/or sulfa agents other than anti-PCP agents. Patients with the following are excluded: * History of ocular, pulmonary, or central nervous system (CNS) toxicity. * CNS lesions or history of CNS lesions. * Neurologic deficits except peripheral neuropathy. * Mild, moderate, severe, or end-stage AIDS dementia complex. Grade 3 or higher nausea and/or vomiting. * Sensitivity to pyrimethamine.