Plasma HIV-1 RNA Dynamics in Antiretroviral-Naive Subjects Receiving either Triple-Nucleoside or Efavirenz-Containing Regimens: ACTG A5166s

Objective. We sought to compare clearance rates of plasma human immunodeficiency virus type 1 (HIV-1) RNA in men and women starting triple-nucleoside-based versus efavirenz (EFV)-based regimens. Methods. First- and second-phase decay rates of plasma HIV-1 were compared in men and women initiating a triple nucleoside reverse-transcriptase inhibitor (NRTI) regimen versus regimens that included EFV plus an NRTI. Subjects (n = 64) were randomized to receive zidovudine/lamivudine/abacavir (triple-nucleoside regimen), zidovudine/lamivudine plus EFV (3-drug EFV regimen) or zidovudine/lamivudine/abacavir plus EFV (4-drug EFV regimen). Plasma HIV-1 RNA levels were fitted to a biexponential viral-dynamics model using a nonlinear mixed-effects model. Nonparametric Wilcoxon tests compared empirical Bayes estimates of first- and second-phase viral decay rates between treatment arms and sex. Results. Median first-phase viral decay rates were significantly faster in subjects receiving the 3-drug EFV regimen (0.67/day), compared with those receiving the triple-nucleoside regimen (0.56/day; P = .02). The second-phase viral decay rate was also faster in the 3-drug EFV group than in the triple-nucleoside group (P = .09). Decay rates in the 4-drug EFV group were intermediate. Viral decay rates were not significantly different in men and women. Conclusions. Faster initial viral decay in subjects randomized to a 3-drug EFV-based regimen corresponded to the overall superior efficacy of that regimen. Viral decay rates did not differ by sex.