Inclusion Criteria

Concurrent Medication:

1. Required for patients with CD4 cell count lower than 200:

• PCP prophylaxis with aerosolized pentamidine, trimethoprim/sulfamethoxazole, mepron, or dapsone.
• Allowed:
• Continuation on an approved antiretroviral agent other than non-nucleoside reverse transcriptase inhibitors (e.g., Nevirapine) or other specifically excluded prior medications, if received without complications for at least 4 weeks prior to study entry.

Patients must have:

• Serologically documented HIV infection.
• Single-dose patients:
• CD4 cell count greater than 50 (no upper limit for single-dose cohorts). Repeated-dose patients:
• CD4 count from 50 to 500 within 35 days prior to entrance on study.
• No active opportunistic infection.

Prior Medication:

Allowed for entry onto multiple-dose study:

• Single-dose portion of S-1153 study, provided all study visits and evaluations are completed, all eligibility criteria are met, and a minimum of 30 days has elapsed before Day 1 of the repeated-dose administration.

Exclusion Criteria

Co-existing Condition:

Patients with the following symptoms or conditions are excluded:

Active opportunistic infection.

Concurrent Medication:

Excluded:

Concomitant use (within 5 half-lives prior to administration and for at least 24 hours following cessation of treatment with S-1153) of highly plasma-bound drugs with narrow therapeutic indices, including but not limited to coumadin and dilantin.

Prior Medication:

1. Investigational new drugs.

• Excluded within 30 days prior to study entry:
• Chronic (greater than 7 days) use of drugs known to affect or be extensively metabolized by cytochromes P450, including but not limited to ketoconazole, fluconazole, itraconazole, isoniazid, rifampin, rifabutin, astemizole, terfenadine, or protease inhibitors.

Prior Treatment:

Excluded within 3 weeks prior to study entry:

• Cytotoxic chemotherapy.
• Interferon treatment.
• Radiation therapy.