Safety and Efficacy of Emtricitabine/Tenofovir Alafenamide as Part of Salvage Antiretroviral Regimens in Patients With Uncontrolled Viremia and Drug-Resistant HIV Infection

Despite the success of antiretroviral therapy (ART), a subset of HIV-1-infected patients have uncontrolled viremia, multiple drug class resistance, and limited treatment options. Tenofovir disoproxil fumarate (TDF) forms part of most ART regimens, however its long-term use is associated with renal tubulopathy and reduced bone mineral density. Viral mutations (eg, K65R, multiple thymidine analog mutations (TAMs) can confer resistance or reduced susceptibility to TDF.

Tenofovir alafenamide (TAF) is an investigational oral prodrug of tenofovir. When compared to TDF, TAF demonstrated lower plasma tenofovir concentrations and more potent antiviral activity at approximately one-tenth of the dose. TAF has the advantage of reduced tenofovir exposure to the renal tubules and bone, potentially resulting in fewer kidney and bone effects. As with TDF, TAF has potent activities against hepatitis B virus (HBV), and may be a treatment option for patients with HIV/HBV co-infections. Phase 2 trials have demonstrated the non-inferiority of TAF to TDF in treating HIV-1 infection in ART-naive patients. Smaller reductions in bone mineral density were measured with TAF than TDF. The most common adverse events were nausea and diarrhea.

This single-arm, single-site, open-label trial will explore the safety and efficacy of TAF in a fixed combination with emtricitabine (FTC) (F/TAF, Gilead Sciences Inc.) as part of a salvage antiretroviral regimen for HIV-1-infected adults and adolescents (greater than or equal to 14 years) who experienced virologic failure. The study will recruit patients who have failed TDF-containing regimens or cannot take TDF (due to resistance mutations or risk of renal injury) and for whom abacavir/lamivudine (ABC/3TC) is not an optimal alternative. Eligible patients will begin 9 days of inpatient directly observed therapy (DOT) with F/TAF plus their pre-enrollment background regimen. On Day 10, patients will switch to F/TAF plus OBT while waiting for the results of Day 10 HIV RNA results. Patients with an HIV RNA decline of <0.5 log10 from Day 1 to Day 10 will discontinue F/TAF, end their study participation, and continue OBT (with TDF/FTC or ABC/3TC in place of F/TAF, as appropriate) under the 14-I-0009 protocol. Patients with a greater than or equal to 0.5 log10 decline in HIV RNA will continue on F/TAF + OBT for 48 weeks, with periodic outpatient assessments of adherence, safety, renal function, bone mineral density, HIV RNA, and CD4 T cell counts. Switching of one or more drugs in an ART regimen due to inadequate viral response will require inpatient DOT under 14-I-0009.