A Study of Pyrimethamine in the Treatment of Infection by a Certain Parasite in HIV-Positive Patients

Inclusion Criteria Concurrent Medication: Allowed: * Aerosolized pentamidine for Pneumocystis carinii pneumonia prophylaxis. * Isoniazid not initiated during study period. * Methadone maintenance. Required: * Stable prescribed dose of zidovudine (AZT) of at least 500 mg/day. Exclusion Criteria Co-existing Condition: Patients with the following conditions or symptoms are excluded: * Prior history of toxoplasmic encephalitis. * Unable to take oral medication reliably or have a malabsorption syndrome (i.e., 3 or more loose stools/day for at least 4 weeks associated with an unintentional weight loss of = or \> 10 percent of body weight). * History of sensitivity to the study medications. Concurrent Medication: Excluded: * Maintenance therapy for opportunistic infections with macrolides or sulfonamides, immunomodulators, rifampin, amphotericin, dapsone, ganciclovir, antifolates, probenecid, benzodiazepines, nephrotoxins, and experimental cytotoxic chemotherapy. * Medications such as aspirin, benzodiazepines, cimetidine, indomethacin, morphine, and sulfonamides should be avoided. Concurrent Treatment: Excluded: * Lymphocyte replacement. Patients with the following are excluded: * Any medical or social condition that, in the opinion of the investigator, would adversely affect either participation or compliance in the study. * Diagnosis of AIDS and febrile and have evidence of another serious opportunistic infection or central nervous system impairment. Prior Medication: Excluded: * Maintenance therapy for opportunistic infections with macrolides or sulfonamides, immunomodulators, rifampin, amphotericin, dapsone, ganciclovir, antifolates, probenecid, benzodiazepines, nephrotoxins, and experimental cytotoxic chemotherapy within past 14 days. Prior Treatment: Excluded: * Lymphocyte replacement within past 14 days. Patients have the following symptoms and conditions: * Laboratory evidence of HIV infection. * Serological evidence of exposure to Toxoplasma gondii, but no clinical evidence of active toxoplasmic infection. * Able to understand and sign a written informed consent. * Either homosexual male or intravenous drug user. Required: * Stable prescribed dose of zidovudine (AZT) of at least 500 mg/day for 4 weeks. Intravenous drug abuse.