Emtricitabine/Tenofovir Alafenamide for Pre-exposure Prophylaxis (PrEP)
Since 2012, the only FDA-approved option for PrEP has been FTC/TDF. This changed in 2019 with the approval of combination emtricitabine/tenofovir alafenamide (FTC/TAF), a structurally similar combination medication. It is now indicated for use in PrEP in uninfected patients at high risk for HIV transmission via sexual intercourse. This excludes patients at risk from receptive vaginal intercourse, as this population has not yet been evaluated.
Approval of PrEP is based on the recent DISCOVER trial, a randomized, double-blind study comparing FTC/TAF with standard-of-care FTC/TDF in reducing the risk of acquiring HIV-1 infection in men and transgender women who have sex with men and are at risk of HIV-1 infection. The trial was conducted as a randomized, double-blind, parallel-group study with a minimum follow-up of 48 weeks, with at least 50% of the participants having 96 weeks of follow-up after randomization. It enrolled 5,399 participants who were randomized 1:1 into either group. The study's primary objective was to assess the incidence of HIV-1 infection per 100 person-years. Among the 2,694 participants in the FTC/TAF arm, HIV-1 incidence was seen in 7 patients (0.16/100 person-years). Among the 2,693 participants in the FTC/TDF arm, HIV-1 incidence was seen in 15 patients (0.34/100 person-years). These incidences demonstrate that FTC/TAF was noninferior to FTC/TDF in study participants who were at risk of acquiring HIV and, ultimately, allowed the FDA to add PrEP to the indications for FTC/TAF.
The place of FTC/TAF in HIV therapy is likely still unclear. While it has found use in other areas of HIV treatment, its benefit over the alternative in this setting is yet to be conclusively determined. While similar, the TAF may offer a lower incidence of bone-density changes and renal dysfunction, adverse effects associated with TDF. This difference is not well established, however, with some data suggesting that, in regimens that do not include a pharmacokinetic booster such as cobicistat or ritonavir, this benefit may not be clinically significant.[27–29]
US Pharmacist. 2020;45(10):17-25. © 2020 Jobson Publishing