To obtain preliminary evidence of antiretroviral activity of 1592U89 when administered in combination with other specific NRTI agents in NRTI experienced patients and to assess the safety and tolerance of multiple oral doses of 1592U89 when administered in combination with specific marketed NRTIs.

Patients will all receive oral doses of 1592U89 in combination with protocol specific current antiretroviral therapy. The treatment groups will be assigned based on each subject's previous NRTI experience.

The study medication is self administered and all evaluations will be performed on an outpatient basis. Patients will be seen at day 0 and weeks 2, 4, 12, 16, 20 and 24.

Inclusion Criteria

Patients must have:

• CD4+ cell count >= 100 /mm3.
• Plasma HIV RNA >= 30,000 copies/ml.
• Study participants may be recruited from all clinical categories, provided they do not meet any of the exclusion criteria.
• Parent or legal guardian to sign written, informed consent for patients under the age of 18.

Exclusion Criteria

Co-existing Condition:

Patients with any of the following symptoms or conditions are excluded:

• Patients with active or ongoing AIDS-defining opportunistic infection or disease. NOTE:
• For this study, a CD4+ cell count <= 200 cells/mm3 in the absence of any other AIDS defining indicator condition is not considered an AIDS defining event.
• Malabsorption syndrome or other gastrointestinal dysfunction that might interfere with drug absorption.
• Patients with life threatening infection or other serious medical conditions whose participation may compromise patient safety.

Concurrent Medication:

Excluded:

• Treatment with cytotoxic chemotherapeutic agents within the 24 weeks of the study.
• Patients receiving other investigational drugs.
• Foscarnet therapy or therapy with other agents with documented activity against HIV in vitro.
• Treatment with immunomodulators.
• Patients on methadone.

Concurrent Treatment:

Excluded:

• Treatment with radiation therapy within the 24 weeks of the study. NOTE:
• Localized radiation therapy may be permitted following consultation with the sponsor.

Patients with any of the following prior conditions are excluded:

• Subjects with a history of lymphoma.
• Subjects with a history of clinically apparent pancreatitis or hepatitis within the last 6 months.

Prior Medication:

Excluded:

• Treatment with any antiretroviral therapy with NRTIs (alone or in combination) other than those defined for each treatment group.
• Treatment with any non-nucleoside RT inhibitors or protease inhibitors.
• Treatment with cytotoxic chemotherapeutic agents within 1 month prior to study entry.
• Investigational HIV vaccine within the past 3 months.
• Immunomodulating agents such as systematic corticosteroids, interleukins, thalidomide, anticytokine agents, anti-oxidants or interferons within 1 month of study entry.

Prior Treatment:

Excluded:

• Treatment with radiation therapy within 1 month of entry.

Risk Behavior:

Excluded:

Patients with current alcohol or illicit drug use that, in the opinion of the principal investigator, may interfere with the patient's ability to comply with the study protocol.