Study to Evaluate the Efficacy of GS-9131 Functional Monotherapy in Human Immunodeficiency Virus (HIV)-1-Infected Adults Failing a Nucleos(t)Ide Reverse Transcriptase Inhibitor-Containing Regimen With Nucleos(t)Ide Reverse Transcriptase Inhibitor Resistant Virus

Part 1 Sentinel Cohort 1: Change From Baseline in Plasma log10 HIV-1 RNA at Day 11

Time frame: Baseline, Day 11

Part 1 Sentinel Cohort 2: Change From Baseline in Plasma log10 HIV-1 RNA at Day 15

Time frame: Baseline, Day 15

Part 1 Randomized Cohort: Change From Baseline in Plasma log10 HIV-1 RNA at Day 15

Time frame: Baseline, Day 15

Part 2: Percentage of Participants With Plasma HIV-1 RNA < 50 Copies/mL as Defined by the FDA Snapshot Analysis at Week 24

The percentage of participants with HIV-1 RNA \< 50 copies/mL at Week 24 was analyzed using the snapshot algorithm, which defines a participant's virologic response status using only the viral load at the predefined time point within an allowed window of time, along with study drug discontinuation status.

Time frame: Week 24

Part 2: Change From Baseline in Plasma log10 HIV-1 RNA at Week 24

Time frame: Baseline, Week 24

Part 2: Change From Baseline in CD4+ Cell Count at Week 24

Time frame: Baseline, Week 24

Part 2: Number of Participants With Treatment Emergent Nucleos(t)Ide Reverse Transcriptase Inhibitor (NRTI) Mutations at the Time of Virologic Failure

Treatment emergent virological failure was defined as an event with an onset date on or after the study drug start date and no later than 30 days after permanent discontinuation of the study drug. Virologic failure was defined as virologic rebound or as suboptimal virologic response in relation to pre-GS-9131 baseline plasma HIV-1 RNA levels. Virological rebound was defined as if participant at any visit after achieving HIV-1 RNA \< 50 copies/mL, a rebound in HIV-1 RNA ≥ 50 copies/mL, or a \>1 log10 increase in HIV-1 RNA from the nadir which was subsequently confirmed at the following scheduled or unscheduled visit. Suboptimal virologic response was defined as plasma HIV-1 RNA ≥ 200 copies/mL and reduction in HIV-1 RNA ≤ 1 log10 from pre-GS-9131 baseline at the Week 8 visit with confirmation at the next scheduled or unscheduled visit.

Time frame: From first dose up to Week 24

Part 2: Number of Participants With Treatment Emergent Protease Inhibitor (PI) Mutations at the Time of Virologic Failure

Treatment emergent virological failure was defined as an event with an onset date on or after the study drug start date and no later than 30 days after permanent discontinuation of the study drug. Virologic failure was defined as virologic rebound or as suboptimal virologic response in relation to pre-GS-9131 baseline plasma HIV-1 RNA levels. Virological rebound was defined as if participant at any visit after achieving HIV-1 RNA \< 50 copies/mL, a rebound in HIV-1 RNA ≥ 50 copies/mL, or a \>1 log10 increase in HIV-1 RNA from the nadir which was subsequently confirmed at the following scheduled or unscheduled visit. Suboptimal virologic response was defined as plasma HIV-1 RNA ≥ 200 copies/mL and reduction in HIV-1 RNA ≤ 1 log10 from pre-GS-9131 baseline at the Week 8 visit with confirmation at the next scheduled or unscheduled visit.

Time frame: From first dose up to Week 24

Part 2: Number of Participants With Treatment Emergent Integrase Strand Transfer Inhibitor (INSTI) Mutations at the Time of Virologic Failure

Treatment emergent virological failure was defined as an event with an onset date on or after the study drug start date and no later than 30 days after permanent discontinuation of the study drug. Virologic failure was defined as virologic rebound or as suboptimal virologic response in relation to pre-GS-9131 baseline plasma HIV-1 RNA levels. Virological rebound was defined as if participant at any visit after achieving HIV-1 RNA \< 50 copies/mL, a rebound in HIV-1 RNA ≥ 50 copies/mL, or a \>1 log10 increase in HIV-1 RNA from the nadir which was subsequently confirmed at the following scheduled or unscheduled visit. Suboptimal virologic response was defined as plasma HIV-1 RNA ≥ 200 copies/mL and reduction in HIV-1 RNA ≤ 1 log10 from pre-GS-9131 baseline at the Week 8 visit with confirmation at the next scheduled or unscheduled visit.

Time frame: From first dose up to Week 24