Triple-drug antiretroviral regimens have become the recommended approach to therapy for HIV infection. [AS PER AMENDMENT 12/4/00: The clinical use of multiple-drug antiretroviral regimens containing various combinations of nucleoside reverse transcriptase inhibitors (NRTIs), nonnucleoside reverse transcriptase inhibitors (NNRTIs), and protease inhibitors (PIs) has become a widespread approach to therapy for HIV infection, especially for patients previously treated with PIs.] Since the introduction of PIs, a greater awareness of the relationship between optimal suppression of viral replication, genotypic resistance, and viral rebound has led to the design of more potent antiretroviral drug combinations. Two ACTG clinical trials addressing the issue of virologic failure utilize antiviral regimens that include 2 NRTIs, 2 PIs (one of which is APV), and EFV (NNRTI). Although this drug combination is logical, there is limited PK data to guide the dosing selection. This study enrolls healthy volunteers to obtain PK profiles and metabolic assessments of APV/EFV before and after the addition of a second PI [AS PER AMENDMENT 12/4/00: APV alone, APV combined with EFV, and APV/EFV combined with a second PI].

Upon study entry, volunteers receive APV plus EFV for 2 weeks. [AS PER AMENDMENT 12/4/00: Volunteers receive a single dose of APV alone on Day 0, EFV alone on Days 1 to 10, and APV combined with EFV on Days 11 to 13.] After 2 weeks [AS PER AMENDMENT 12/4/00: After completion of the second PK visit], volunteers are randomized to 1 of 5 treatment arms to add a second PI to the APV/EFV drug combination for 2 more weeks [AS PER AMENDMENT 12/4/00: for at least 1 week]. The treatment arms are as follows:

Arm A (control arm): APV and EFV alone. Arm B: APV and EFV plus IDV [AS PER AMENDMENT 12/4/00: APV and EFV plus NFV]. Arm C: APV and EFV plus NFV [AS PER AMENDMENT 12/4/00: APV and EFV plus IDV]. Arm D: APV and EFV plus RTV sgc. Arm E: APV and EFV plus SQV sgc. On Day 14, 15, or 16, volunteers return to the clinic for PK testing following the dual-drug regimen, and again on Day 29, 30, or 31 following the triple-drug regimen (or continued dual-drug regimen for Arm A). [AS PER AMENDMENT 12/4/00: Volunteers attend clinics for PK testing on Days 0 and 1 (first visit), after taking the dual-drug regimen for at least 3 days (second visit, e.g., on Day 14 or after), and after taking the triple-drug regimen (or, if in Arm A, after continuing on the dual-drug regimen) for at least 7 days (third visit).] Before each PK testing, volunteers complete an Adherence Questionnaire. [AS PER AMENDMENT 12/4/00: The Adherence Questionnaire is administered at the second and third PK visits.] Volunteers maintain a food diary. Two to three weeks after completing the drug regimen [AS PER AMENDMENT 12/4/00: Within 2-3 weeks after the third PK visit], volunteers return to the clinic for evaluations and urine and blood sampling.