Tenofovir/emtricitabine (TDF/FTC) and abacavir/lamivudine (ABC/3TC) are widely used with ritonavir (RTV)-boosted protease inhibitors (PIs) as first-line highly active antiretroviral therapy (HAART), but there is conflicting evidence on their relative efficacy. The ACTG 5202 and BICOMBO trials suggested higher efficacy for TDF/FTC, whereas the HEAT trial showed no efficacy difference between the nucleoside reverse transcriptase inhibitor (NRTI) backbones.
A systematic MEDLINE search identified 21 treatment arms in 12 clinical trials of 5168 antiretroviral-naïve patients, where TDF/FTC (n=3399) or ABC/3TC (n=1769) was used with RTV-boosted PI. For each NRTI backbone and RTV-boosted PI, the percentage of patients with viral load <50 HIV-1 RNA copies/mL at week 48 by standardized Intent to Treat, Time to Loss of Virological Failure (ITT TLOVR) analysis were combined using inverse-variance weighting. The effect of baseline HIV RNA, CD4 cell count and choice of NRTI backbone were examined using a weighted analysis of covariance.
Across all the trials, HIV RNA suppression rates were significantly higher for those with baseline viral load below 100 000 copies/mL (77.2%) vs. above 100 000 copies/mL (70.9%) (P=0.0005). For the trials of lopinavir/ritonavir (LPV/r), atazanavir/ritonavir (ATV/r) and fosamprenavir/ritonavir (FAPV/r) using either TDF/FTC or ABC/3TC, the HIV RNA responses were significantly lower when ABC/3TC was used, relative to TDF/FTC, for all patients (P=0.0015) and for patients with baseline viral load <100 000 copies/mL (70.1%vs. 80.6%, P=0.0161), and was borderline for those with viral load >100 000 copies/mL (67.5%vs. 71.5%, P=0.0523).
This systematic meta-regression analysis suggests higher efficacy for first-line use of a TDF/FTC NRTI backbone with boosted PIs, relative to use of ABC/3TC. However, this effect may be confounded by differences between the trials in terms of baseline characteristics, patient management or adherence.