In this open-label, multicenter, multinational study, ZDV is replaced with d4T in ZDV-containing regimens, or d4T is added to non-ZDV-containing regimens in 20 patients experiencing ADC. Patients are defined as having failed treatment if they progress by one ADC stage on the MSK (Memorial Sloan Kettering) rating scale on study (i.e., from Stage 1 to 2 or Stage 2 to 3). Patients are evaluated on a weekly basis until the dementia deterioration is confirmed to be caused by HIV-1. The effect of d4T-containing regimens is assessed for the following parameters: neurological status, survival, AIDS-defining conditions, CSF (cerebrospinal fluid) and plasma viral load, CSF and blood immunological markers, blood CD4 cell counts, and viral resistance. This study also assesses the pharmacokinetics of d4T in the CSF and in the blood.

Inclusion Criteria

You may be eligible for this study if you:

• Are HIV-positive.
• Are at least 13 years old (need consent if under 18).
• Have AIDS Dementia Complex.
• Have been on a stable anti-HIV drug regimen for at least 8 weeks prior to study entry.
• Agree to use effective methods of birth control during the study.
• Are available for at least 16 weeks of study.

Exclusion Criteria

You will not be eligible for this study if you:

• Have ever taken d4T.
• Have a neurological (brain/spinal cord) disease, such as chronic seizures or head injury, or certain other conditions that would interfere with your ability to complete the study.
• Are pregnant or breast-feeding.
• Abuse alcohol or drugs.
• Have peripheral neuropathy or a newly diagnosed AIDS-defining infection that requires treatment at the time of study enrollment.
• Have received certain medications.
• Cannot take medications by mouth.
• Have severe diarrhea for at least 7 days in a row within 30 days prior to study entry.