Study of Bictegravir/Emtricitabine/Tenofovir Alafenamide Fixed Dose Combination in Adolescents and Children With Human Immunodeficiency Virus-1

Study Overview
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Brief Summary
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The goals of this clinical study are to learn how Bictegravir/Emtricitabine/Tenofovir Alafenamide fixed dose combination (FDC) interacts with the body, confirm the dose, and also to learn more about the safety and tolerability of Bictegravir/Emtricitabine/Tenofovir Alafenamide FDC in adolescents and children with HIV-1.

Official Title
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A Phase 2/3, Open-Label Study of the Pharmacokinetics, Safety, and Antiviral Activity of the GS-9883/Emtricitabine/Tenofovir Alafenamide (GS-9883/F/TAF) Fixed Dose Combination (FDC) in HIV-1 Infected Adolescents and Children

Conditions
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HIV-1 Infection

Intervention / Treatment
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* Drug: B/F/TAF (Adult Strength)
* Drug: B/F/TAF (Low Dose)
* Drug: B/F/TAF (TOS)
* Drug: B/F/TAF (TOS)
* Drug: B/F/TAF (TOS)
* Drug: B/F/TAF (TOS)


Participation Criteria
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Eligibility Criteria
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Key Inclusion Criteria: Cohort 1: HIV-1 infected adolescents (12 to < 18 years of age and screening weight ≥ 35 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 2: HIV-1 infected children (6 to < 12 years of age and screening weight ≥ 25 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 3: HIV-1 infected children (≥ 2 years of age and screening weight of ≥ 14 to < 25 kg) who are virologically suppressed for ≥ 6 months prior to screening. Cohort 4 Group 1: HIV-1 infected children (≥ 2 years of age and screening weight of ≥ 14 to < 25 kg) who are virologically suppressed for ≥ 6 months prior to screening and unable to swallow tablets. Documented plasma HIV-1 RNA < 50 copies/mL on a stable regimen (or undetectable HIV-1 RNA level according to the local assay being used if the limit of detection is ≥ 50 copies/mL) for ≥ 6 months preceding the Screening visit. Unconfirmed virologic elevations of ≥ 50 copies/mL (transient detectable viremia, or blip) prior to screening are acceptable. If the lower limit of detection of the local HIV-1 RNA assay is < 50 copies/mL (eg, < 20 copies/mL), the plasma HIV-1 RNA level cannot exceed 50 copies/mL on two consecutive HIV-1 RNA tests. Stable antiretroviral regimen of 2 nucleoside reverse transcriptase inhibitors (NRTIs) in combination with a third agent for a minimum of 6 months prior to the screening visit. Individuals undergoing dose modifications to their antiretroviral regimen for growth or who are switching medication formulation(s) are considered to be on a stable antiretroviral regimen. Estimated glomerular filtration rate (GFR) ≥ 90 mL/min/1.73 m^2 according to the Schwartz Formula No documented or suspected resistance to emtricitabine (FTC), tenofovir (TFV), or integrase strand transfer inhibitors (INSTIs) including, but not limited to, the reverse transcriptase resistance mutations K65R and M184V/I Cohort 4 Group 2-4: HIV-1 infected children (≥ 1 month of age and screening weight of ≥ 3 to < 14 kg) who are treatment naive or on ARV treatment for ≥ 1 month prior to screening Positive confirmatory HIV test (confirmatory nucleic acid-based testing if < 18 months of age) On a stable ARV regimen for ≥ 1 month or treatment naive (Individual is considered treatment naive if ARVs were given for prevention of mother-to-child transmission but not for HIV treatment) For < 1 year of age, eGFR ≥ the minimum normal values for age according to the information below using the Schwartz Formula 30 mL/min/1.73 m^2 for age > 2 months to ≤ 95 days 39 mL/min/1.73 m^2 for age ≥ 96 days to ≤ 6 months 49 mL/min/1.73 m^2 for age > 6 months to < 12 months For ≥ 1 year of age, eGFR ≥ 90 mL/min/1.73 m^2 using the Schwartz Formula No documented or suspected resistance to FTC, TFV, or INSTIs including, but not limited to, the reverse transcriptase resistance mutation K65R. For individuals < 14 kg, M184V/I AND HIV-1 RNA < 50 copies/mL will be allowed. Individuals with HIV-1 RNA > 50 copies/mL should not have FTC, TFV, or INSTI resistance mutations. Last dose of nevirapine (NVP) or efavirenz (EFV), if applicable, ≥ 14 days prior to enrollment Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Ages Eligible for Study
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Minimum Age: 1 Month
Maximum Age: 17 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Non-Randomized
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Cohort 1 (12 to < 18 years of age and weight ≥ 35 kg)<br>Part A: Participants will participate in an Intensive PK evaluation at Week 2 or Week 4 and continue to receive the adult strength B/F/TAF FDC through Week 48. Part B: Following confirmation of BIC PK data from Cohort 1 Part A, participants will receive the adult strength B/F/TAF through Week 48. | Drug: B/F/TAF (Adult Strength)<br>* 50/200/25 mg FDC tablets administered orally once daily without regard to food<br>* Other names: Biktarvy®;|
| Experimental: Cohort 2 (6 to < 12 years of age and weight ≥ 25 kg)<br>Part A: Participants will participate in an Intensive PK evaluation at Week 2 or Week 4 and continue to receive the adult strength B/F/TAF FDC through Week 48. Part B: Following confirmation of BIC PK data from Cohort 2 Part A, participants will receive the adult strength B/F/TAF FDC through Week 48. | Drug: B/F/TAF (Adult Strength)<br>* 50/200/25 mg FDC tablets administered orally once daily without regard to food<br>* Other names: Biktarvy®;|
| Experimental: Cohort 3 (≥ 2 years of age and weight ≥ 14 to < 25 kg)<br>Part A: Participants will participate in an Intensive PK evaluation at Week 2 after which they will continue to receive the low dose B/F/TAF FDC tablet through Week 48. Part B: Following confirmation of BIC PK data from Cohort 3 Part A, participants will receive the low dose B/F/TAF FDC tablet through Week 48. | Drug: B/F/TAF (Low Dose)<br>* 30/120/15 mg FDC tablets administered orally once daily without regard to food<br>* Other names: GS-9883/F/TAF;|
| Experimental: Cohort 4 Group 1 (≥ 2 years of age and weight ≥ 14 to < 25 kg)<br>Due to Cohort 3 Part A Intensive PK evaluation at Week 2 with the low dose B/F/TAF FDC tablet, participants will not participate in an Intensive PK evaluation at Week 2. Participants will receive B/F/TAF FDC tablets for oral suspension (TOS) once daily through Week 48. | Drug: B/F/TAF (TOS)<br>* 2 x FDC of bictegravir 15 mg/emtricitabine 60 mg/ tenofovir alafenamide 7.5 mg (B/F/TAF 15/60/7.5 mg) (total dose 30/120/15 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;|
| Experimental: Cohort 4 Group 2 (≥ 1 month of age and weight ≥ 10 to < 14 kg)<br>Participants will participate in an Intensive PK evaluation at Week 2 after which they will continue to receive B/F/TAF FDC TOS twice daily through Week 48. | Drug: B/F/TAF (TOS)<br>* FDC of bictegravir 15 mg/emtricitabine 60 mg/ tenofovir alafenamide 7.5 mg (B/F/TAF 15/60/7.5 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;|
| Experimental: Cohort 4 Group 3 (≥ 1 month of age and weight ≥ 6 to < 10 kg)<br>Participants will participate in an Intensive PK evaluation at Week 2 after which they will continue to receive B/F/TAF FDC TOS twice daily through Week 48. | Drug: B/F/TAF (TOS)<br>* 2 x FDC of bictegravir 3.75 mg/emtricitabine 15 mg/ tenofovir alafenamide 1.88 mg (B/F/TAF 3.75/15/1.88 mg) (total dose 7.5/30/3.75 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;|
| Experimental: Cohort 4 Group 4 (≥ 1 month of age and weight ≥ 3 to < 6 kg)<br>Participants will participate in an Intensive PK evaluation at Week 2 after which they will continue to receive B/F/TAF FDC TOS twice daily through Week 48. | Drug: B/F/TAF (TOS)<br>* FDC of bictegravir 3.75 mg/emtricitabine 15 mg/ tenofovir alafenamide 1.88 mg (B/F/TAF 3.75/15/1.88 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;|
| Experimental: Open-Label Extension<br>Following Week 48, participants in countries where B/F/TAF is not available may have the option to receive adult strength B/F/TAF FDC, low dose B/F/TAF FDC, or B/F/TAF FDC TOS (based on age and weight) until it becomes available for use according to the participant's age and weight or the product becomes accessible to participants through an access program. | Drug: B/F/TAF (Adult Strength)<br>* 50/200/25 mg FDC tablets administered orally once daily without regard to food<br>* Other names: Biktarvy®;Drug: B/F/TAF (Low Dose)<br>* 30/120/15 mg FDC tablets administered orally once daily without regard to food<br>* Other names: GS-9883/F/TAF;Drug: B/F/TAF (TOS)<br>* 2 x FDC of bictegravir 15 mg/emtricitabine 60 mg/ tenofovir alafenamide 7.5 mg (B/F/TAF 15/60/7.5 mg) (total dose 30/120/15 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;Drug: B/F/TAF (TOS)<br>* FDC of bictegravir 15 mg/emtricitabine 60 mg/ tenofovir alafenamide 7.5 mg (B/F/TAF 15/60/7.5 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;Drug: B/F/TAF (TOS)<br>* 2 x FDC of bictegravir 3.75 mg/emtricitabine 15 mg/ tenofovir alafenamide 1.88 mg (B/F/TAF 3.75/15/1.88 mg) (total dose 7.5/30/3.75 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;Drug: B/F/TAF (TOS)<br>* FDC of bictegravir 3.75 mg/emtricitabine 15 mg/ tenofovir alafenamide 1.88 mg (B/F/TAF 3.75/15/1.88 mg) administered orally as TOS, once daily without regard to food<br>* Other names: GS-9883/F/TAF;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| PK Parameter: AUCtau of Bictegravir | AUCtau is defined as concentration of drug over time (the area under the concentration verses time curve over the dosing interval). Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Ctau of Bictegravir | Ctau is defined as the observed drug concentration at the end of the dosing interval. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: AUClast of TAF (Cohort 4) | AUClast is defined as area under the concentration versus time curve from time zero to the last quantifiable concentration. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Cmax of TAF (Cohort 4) | Cmax is defined as maximum observed concentration of drug. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| Percentage of Participants Experiencing Treatment-Emergent Adverse Events (AEs) Through Week 24 |  | Up to 24 weeks | 
| Percentage of Participants Experiencing Treatment-Emergent Laboratory Abnormalities Through Week 24 |  | Up to 24 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Proportion of Participants with Plasma HIV-1 RNA < 50 copies/mL at Week 24 as Defined by the US FDA-Defined Snapshot Algorithm |  | Week 24 | 
| Proportion of Participants with Plasma HIV-1 RNA < 50 copies/mL at Week 48 as Defined by the US FDA-Defined Snapshot Algorithm |  | Week 48 | 
| Change from Baseline in CD4+ Cell Counts at Week 24 |  | Baseline, Week 24 | 
| Change from Baseline in CD4+ Cell Counts at Week 48 |  | Baseline, Week 48 | 
| Change from Baseline in CD4+ Cell Count Percentages at Week 24 |  | Baseline, Week 24 | 
| Change from Baseline in CD4+ Cell Count Percentages at Week 48 |  | Baseline, Week 48 | 
| PK Parameter: Tmax of Bictegravir | Tmax is defined as the time (observed time point) of Cmax. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Cmax of Bictegravir | Cmax is defined as the maximum observed concentration of drug. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: AUClast of Bictegravir | AUClast is defined as the area under the concentration of drug from time zero to the last observable concentration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: T1/2 of Bictegravir | T1/2 is defined as the estimate of the terminal elimination half-life of the drug. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Apparent Clearance (CL) of Bictegravir | CL is defined as the systemic clearance of the drug following study drug administration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Apparent Vz of Bictegravir | Vz is defined as the volume of distribution of the drug after study drug administration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: AUCtau of TAF and FTC | AUCtau is defined as concentration of drug over time (the area under the concentration verses time curve over the dosing interval). Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: AUClast of TAF and FTC (Cohorts 1, 2, and 3) | AUClast is defined as the area under the concentration of drug from time zero to the last observable concentration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose | 
| PK Parameter: AUClast of FTC (Cohorts 4) | AUClast is defined as area under the concentration versus time curve from time zero to the last quantifiable concentration. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Cmax of TAF and FTC (Cohorts 1, 2, and 3) | Cmax is defined as the maximum observed concentration of drug. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose | 
| PK Parameter: Cmax of FTC (Cohorts 4) | Cmax is defined as maximum observed concentration of drug. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Ctau of TAF and FTC | Ctau is defined as the observed drug concentration at the end of the dosing interval. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Tmax of TAF and FTC | Tmax is defined as the time (observed time point) of Cmax. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: T1/2 of TAF and FTC | T1/2 is defined as the estimate of the terminal elimination half-life of the drug. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Apparent CL of TAF and FTC | CL is defined as the systemic clearance of the drug following study drug administration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| PK Parameter: Apparent Vz of TAF and FTC | Vz is defined as the volume of distribution of the drug after study drug administration. Cohorts 1 & 2 Part A will participate in an Intensive PK Evaluation at Week 2 or Week 4. Samples will be collected at 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, and 24 hours post-dose. Cohort 3 Part A will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, and 24 hours post-dose. Cohort 4 Groups 2, 3, and 4 participants will participate in an Intensive PK evaluation at Week 2. Samples will be collected at 0 (pre-dose) 0.5, 1, 2, 4, and 8 hours post-dose. | Week 2 or Week 4 for Cohorts 1 & 2: 0 (pre-dose), 0.5, 1, 2, 3, 4, 6, 8, & 24 hours postdose; Week 2 for Cohort 3: 0 (pre-dose), 0.25, 0.5, 1, 1.5, 2, 3, 4, 5, 8, & 24 hours post-dose; Week 2 for Cohort 4: 0 (predose) 0.5, 1, 2, 4, & 8 hours postdose | 
| Percentage of Participants Experiencing Treatment-Emergent Adverse Events Through Week 48 |  | Up to 48 weeks | 
| Percentage of Participants Experiencing Treatment-Emergent Laboratory Abnormalities Through Week 48 |  | Up to 48 weeks | 
| Acceptability of B/F/TAF Formulation at Day 1 (All Cohorts) | Participants or legal guardian will be asked: if study drug shape and size were acceptable (for Cohort 1 and Cohort 2) about ease of swallowability and the shape and size of study drug when swallowed (for Cohort 3) about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste (for Cohort 4) | Day 1 | 
| Palatability of B/F/TAF Formulation at Day 1 (All Cohorts) | Participants or legal guardian will be asked about the study drug taste (All Cohorts) | Day 1 | 
| Acceptability of B/F/TAF Formulation at Week 4 (All Cohorts) | Participants or legal guardian will be asked: if study drug shape and size were acceptable (for Cohort 1 and Cohort 2) about ease of swallowability and the shape and size of study drug when swallowed (for Cohort 3). about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste (for Cohort 4) | Week 4 | 
| Palatability of B/F/TAF Formulation at Week 4 (All Cohorts) | Participants or legal guardian will be asked about the study drug taste (All Cohorts) | Week 4 | 
| Acceptability of B/F/TAF Formulation at Week 24 (Cohort 3 and Cohort 4) | Participants or legal guardian will be asked: about ease of swallowability and the shape and size of study drug when swallowed (for Cohort 3). about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste (for Cohort 4) | Week 24 | 
| Palatability of B/F/TAF Formulation at Week 24 (Cohort 3 and Cohort 4) | Participants or legal guardian will be asked about the study drug taste | Week 24 | 
| Acceptability of B/F/TAF Formulation at Week 48 (Cohort 3 and Cohort 4) | Participants or legal guardian will be asked: about ease of swallowability and the shape and size of study drug when swallowed (for Cohort 3). about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste (for Cohort 4) | Week 48 | 
| Palatability of B/F/TAF Formulation at Week 48 (Cohort 3 and Cohort 4) | Participants or legal guardian will be asked about the study drug taste | Week 48 | 
| Acceptability of B/F/TAF Formulation at Week 1 (Cohort 4) | Participants or legal guardian will be asked about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste | Week 1 | 
| Palatability of B/F/TAF Formulation at Week 1 (Cohort 4) | Participants or legal guardian will be asked about the study drug taste | Week 1 | 
| Acceptability of B/F/TAF Formulation at Week 2 (Cohort 4) | Participants or legal guardian will be asked about their understanding of instructions, preparation of the study drug formulation and study drug administration and taste | Week 2 | 
| Palatability of B/F/TAF Formulation at Week 2 (Cohort 4) | Participants or legal guardian will be asked about the study drug taste | Week 2 |