Researchers at the 2016 Conference on Retroviruses and Opportunistic Infections presented results from a randomized double-blind, double-dummy switch study of TAF/FTC. Over 660 patients with virologic suppression on TDF/FTC-containing 3-drug regimens were either switched to TAF/FTC (200/10 mg with boosted PIs, 200/25 mg without boosters) or continued on TDF/FTC; the background third agents were not changed. At 48 weeks, 94.3% of TAF/FTC recipients and 93% of TDF/FTC recipients maintained HIV RNA suppression; the difference was not significant. One patient with virologic failure in the TAF arm developed the M184V mutation; no other patients developed resistance.
There were no notable differences between groups in symptomatic adverse events. The estimated glomerular filtration rate (eGFR) improved somewhat in both groups, but more so in the TAF group (8.4 mL/min vs 2.8 mL/min; p < .001). Albuminuria and proteinuria improved significantly in TAF recipients but worsened in TDF recipients, as has been seen in other studies of TAF. Bone mineral density at spine and hip improved by a mean of 1-1.5% in TAF recipients and did not change significantly in TDF recipients. Those who switched to TAF had modest increases in total and LDL cholesterol and in triglycerides.
Clinical Bottom Line
In this and other switch studies that have compared TAF with TDF, the two tenofovir prodrugs appear to be equally effective in suppressing HIV. TAF's effects on laboratory markers of renal function and on bone mineral density have been quite consistent in various studies. TAF appears to cause less proteinuria than does TDF, but possible differences in effects on eGFR appear modest; further study will be needed to define the renal safety profile of TAF. Note that TAF has been compared only with TDF, and not with other NRTIs or other ARVs. TAF does appear to have beneficial effects on bone mineral density compared with TDF.
Thus, there appears to be no disadvantage to using TAF instead of TDF, and if proven over time, there may be significant advantages. A couple of cautions, however: 1) there are no clinical studies on TAF's use in preexposure prophylaxis (PrEP) -- further study is needed before it can be used for prevention (see Tissue Levels of TAF: Too Low for PrEP?); 2) there are limited data for use in HIV/HBV coinfection (though the available data look promising); and 3) dosage depends on the accompanying ARVs: 10 mg daily if a PK booster (ritonavir or cobicistat) is used, 25 mg daily otherwise.
FDA approval of a TAF/FTC coformulation is expected soon.