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Inclusion Criteria

Concurrent Medication:

Allowed:

• AZT.

Patients must have:

• Documented HIV infection as determined by a positive ELISA and/or Western blot.
• Absolute CD4 count of 100 - 500 cells/mm3 within 90 days prior to registration OR a CD4 count of 50 - 99 cells/mm3 within 30 days prior to registration.
• Prior zidovudine therapy for at least 6 months and currently tolerating at least 500 mg daily.

Exclusion Criteria

Co-existing Condition:

Patients with the following symptoms and conditions are excluded:

• Newly diagnosed AIDS-defining opportunistic infection requiring acute therapy at time of enrollment.
• Need for chronic systemic therapy at time of enrollment.
• Intractable diarrhea.
• Signs or symptoms of bilateral peripheral neuropathy at time of screening.
• Demonstrated intolerance to zidovudine therapy.
• Any other clinical conditions that would render the patient unsuitable for study or unable to comply with the dosing requirements.

Concurrent Medication:

Excluded:

• Chronic systemic therapy with agents likely to suppress bone marrow, cause neurotoxicity, or create hepatic dysfunction.

Patients with the following prior conditions are excluded:

• Prior history of bilateral peripheral neuropathy.
• Demonstrated intolerance to zidovudine therapy.

Prior Medication:

Excluded:

• Prior d4T, ddI, or ddC.
• Other investigational antiretroviral drugs (e.g., AZddU, Al 721, interferon, or immunomodulating drugs within 1 month prior to study entry or ribavirin within 3 months prior to study entry).
• Prior myelosuppressive, neurotoxic, or cytotoxic anticancer therapy within 3 months prior to study entry.
• Any prior therapy that would render the patient unsuitable for study or unable to comply with dosing requirements.

Required:

• At least 6 months of prior AZT and currently tolerating at least 500 mg daily, with the last dose received no more than 7 days prior to study entry.