The purpose of this study is to see if it is safe and effective to give T-20, a new type of anti-HIV drug, with a combination of other anti-HIV drugs. The other anti-HIV drugs used are abacavir (ABC), amprenavir (APV), ritonavir (RTV), and efavirenz (EFV). Three different doses of T-20 are tested.

Patients are assigned to one of four groups. Three dose groups receive a background antiretroviral regimen (ABC, APV, RTV, and EFV) and T-20, which is given at one of three doses on a twice-daily regimen. The fourth group (control) receives the background antiretroviral regimen alone. For each treatment group, 17 patients are enrolled. Treatment is administered for 16 weeks, followed by a 32-week treatment extension, and a 2-week follow-up period. The following are assessed throughout the trial: safety parameters (as measured by hematology, clinical chemistry, urinalysis, and treatment-emergent adverse events); virologic and immunologic activity; phenotypic and genotypic resistance; T-20 plasma levels; and pharmacokinetics of T-20 and oral antiretrovirals. The total study duration is 1 year.

Inclusion Criteria

Patients may be eligible for this study if they:

• Are HIV-positive.
• Have an HIV level (viral load) between 400 and 100,000 copies/ml at the screening visit.
• Have taken at least 1 PI (protease inhibitor) for at least 16 weeks, and have had no interruptions in their most recent PI-containing anti-HIV drug regimen.
• Are at least 18 years old.
• Agree to abstinence or use of 2 effective methods of birth control, including a barrier method, during the study.

Exclusion Criteria

Patients will not be eligible for this study if they:

• Have ever taken an NNRTI (nonnucleoside reverse transcriptase inhibitor).
• Have an opportunistic (HIV-related) infection.
• Have had an unexplained fever of at least 38.5 C for 7 days in a row within 30 days prior to screening.
• Have had diarrhea lasting at least 15 days within 30 days prior to screening.
• Have ever taken abacavir, amprenavir, or efavirenz (ABC, APV, or EFV).
• Have certain genetic characteristics (drug resistance mutations) that could change the way a drug acts in the body.
• Are allergic to any of the study medications.
• Have a tumor other than certain skin or cervical cancers.
• Are on chemotherapy that cannot be discontinued during the study.
• Are taking an investigational drug within 30 days prior to screening.
• Have ever received an HIV vaccine.
• Are taking certain medications.
• Abuse drugs or alcohol.
• Have hemophilia or another blood clotting disorder.
• Have had an organ transplant.
• Are pregnant or breast-feeding.