Current treatment guidelines recommend combination regimens of 2 nucleoside analogues with either a PI or an NNRTI for the initial treatment of HIV infection. However, the efficacy of current regimens is limited by their complexity, pharmacokinetic characteristics, short- and long-term side effects, and drug-resistance profiles at the time of virologic failure. Consequently, the identification of new initial regimens that are simpler, better tolerated, preserve treatment options in the event of failure, and improve antiretroviral potency is needed. In addition, recent concern over the long-term toxicities of PIs and the extensive cross-resistance among the available PIs have led to the testing of PI-sparing regimens.

Participants will be in this study for a minimum of 120 weeks and a maximum of approximately 4 years. In Step 1, patients are randomly selected to receive 1 of 3 blinded treatment regimens: abacavir (ABC)/lamivudine (3TC)/zidovudine (ZDV)/efavirenz (EFV), ABC/3TC/ZDV, or 3TC/ZDV/EFV. Patients with confirmed virologic failure on Step 1 and two successive plasma HIV RNA levels of 10,000 copies/ml or greater must register to Step 2. Patients with confirmed virologic failure on Step 1 and whose plasma HIV RNA is under 10,000 copies/ml may remain on Step 1 or register to Step 2. [AS PER AMENDMENT 04/11/03: Discontinuation of Arm B was recommended. Consequently, Arms A and C were unblinded to EFV but not to ABC. A number of options are available for patients originally randomized to Arm B.]

Step 2 is open label. Regimens include 2 or 3 nucleoside reverse transcriptase inhibitors (NRTIs) in combination with EFV, atazanavir (ATZ), ritonavir-boosted ATZ, or tenofovir disoproxil fumarate (TDF). Patients on Arm B treatment who have an HIV RNA level less than 200 copies/ml within the past 8 weeks are eligible for randomization to open-label intensification of Arm B on Step 3.

Step 3 regimens include ABC/3TC/ZDV plus either EFV or TDF. Patients with evidence of treatment-limiting toxicity to Step 3 study drugs have the option of substituting d4T for ZDV, ddI for ABC or TDF, and/or NVP for EFV. Patients with confirmed virologic failure on Step 3 and whose plasma HIV RNA is less than 10,000 copies/ml may either remain on Step 3 or register to Step 4. Patients with two successive plasma HIV RNA levels of 10,000 copies/ml or greater on Step 3 must register to Step 4.

Step 4 is open label. Regimens include two or three NRTIs plus EFV, ATV, ritonavir-boosted ATV, or TDF. Clinical assessments and laboratory evaluations are done at entry, at Weeks 2, 4, 6, 8, 12, 16, 20, 24, and then every 8 weeks thereafter for the duration of the study. Evaluations are also required when a protocol-allowed drug substitution is made.

In addition, 3 substudies are being conducted: a neurology substudy for efavirenz, a pharmacology substudy for atazanavir, and a viral dynamics substudy.