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.