Repeat testing of low-level HIV-1 RNA: assay performance and implementation in clinical trials.

OBJECTIVE: Assess the performance of HIV-1 RNA repeat testing of stored samples in cases of low-level viremia during clinical trials. DESIGN: Prospective and retrospective analysis of randomized clinical trial samples and reference standards. METHODS: To evaluate assay variability of the Cobas AmpliPrep/Cobas TaqMan HIV-1 Test, v2.0, three separate sources of samples were utilized: the World Health Organization (WHO) HIV reference standard (assayed using 50 independent measurements at six viral loads <200 copies/ml), retrospective analysis of four to six aliquots of plasma samples from four clinical trial participants, and prospective repeat testing of 120 samples from participants in randomized trials with low-level viremia. RESULTS: The TaqMan assay on the WHO HIV-1 RNA standards at viral loads <200 copies/ml performed within the expected variability according to assay specifications. However, standards with low viral loads of 36 and 18 copies/ml reported values of ≥ 50 copies/ml in 66 and 18% of tests, respectively. In participants treated with antiretrovirals who had unexpected viremia of 50-200 copies/ml after achieving <50 copies/ml, retesting of multiple aliquots of stored plasma found <50 copies/ml in nearly all cases upon retesting (14/15; 93%). Repeat testing was prospectively implemented in four clinical trials for all samples with virologic rebound of 50-200 copies/ml (n = 120 samples from 92 participants) from which 42% (50/120) had a retest result of less than 50 copies/ml and 58% (70/120) retested ≥ 50 copies/ml. CONCLUSION: The TaqMan HIV-1 RNA assay shows variability around 50 copies/ml that affects clinical trial results and may impact clinical practice. In participants with a history of viral load suppression, unexpected low-level viremia may be because of assay variability rather than low drug adherence or true virologic failure. Retesting a stored aliquot of the same sample may differentiate between assay variability and virologic failure as the source of viremia. This retesting strategy could save time, money, and anxiety for patients and their providers, as well as decrease follow-up clinic visits without increasing the risk of virologic failure and resistance development.

Efficacy and safety of emtricitabine/tenofovir alafenamide (FTC/TAF) vs. emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) as a backbone for treatment of HIV-1 infection in virologically suppressed adults: subgroup analysis by third agent of a randomized, double-blind, active-controlled phase 3 trial.

BACKGROUND: FTC/TAF was shown to be noninferior to FTC/TDF with advantages in markers of renal and bone safety. OBJECTIVE: To evaluate the efficacy and safety of switching to FTC/TAF from FTC/TDF by third agent (boosted protease inhibitor [PI] vs. unboosted third agent). METHODS: We conducted a 48-week subgroup analysis based on third agent from a randomized, double blind study in virologically suppressed adults on a FTC/TDF-containing regimen who switched to FTC/TAF vs. continued FTC/TDF while remaining on the same third agent. RESULTS: We randomized (1:1) 663 participants to either switch to FTC/TAF (N = 333) or continue FTC/TDF (N = 330), each with baseline third agent stratifying by class of third agent in the prior treatment regimen (boosted PI 46%, unboosted third agent 54%). At week 48, significant differences in renal biomarkers and bone mineral density were observed favoring FTC/TAF over FTC/TDF (p < 0.05 for all), with similar improvements in the FTC/TAF arm in those who received boosted PI vs. unboosted third agents. At week 48, virologic success rates were similar between treatment groups for those who received a boosted PI (FTC/TAF 92%, FTC/TDF 93%) and for those who received an unboosted third agent (97% vs. 93%). CONCLUSIONS: In virologically suppressed patients switching to FTC/TAF from FTC/TDF, high rates of virologic suppression were maintained, while renal and bone safety parameters improved, regardless of whether participants were receiving a boosted PI or an unboosted third agent. FTC/TAF offers safety advantages over FTC/TDF and can be an important option as an NRTI backbone given with a variety of third agents.

Switching from ritonavir to cobicistat in HIV patients with renal impairment who are virologically suppressed on a protease inhibitor.

INTRODUCTION: Cobicistat (COBI) is a pharmacoenhancer and one of the components of ECF/TDF (elvitegravir/cobicistat/emtricitabine/tenofovir DF), which is approved in treatment-naïve HIV patients with creatinine clearance (CrCl) ≥70 mL/min. Study 118 assessed the renal safety of COBI-containing regimens in HIV patients with mild to moderate renal impairment. MATERIAL AND METHODS: Phase 3, open label study in HIV-1-infected patients with CrCl 50-89 mL/min who are virologically suppressed on a stable regimen containing ritonavir (RTV)-boosted atazanavir (ATV) or darunavir (DRV). Patients switched RTV to COBI, while keeping the rest of their regimen unchanged. We present the 96-week (Wk) data. RESULTS: Seventy-three patients were enrolled. Mean age was 54 years; male 82%; white 77%; hypertension 38%; diabetes 18%; baseline proteinuria (≥trace) 51%; median CrCl 71 mL/min (range: 42-98). At Wk 96, 89% maintained virologic suppression (95% CI 77.4-95.8%). No emergent resistance developed. Reductions in CrCl (median [IQR]) were observed as early as Wk 2, after which they were nonprogressive through Wk 96 (Wk 48: -3.8 [-9-0.8]; Wk 96: -5.0 [-13.0-0.1]). Changes in CrCl by baseline CrCl (<70 vs ≥70) at Wk 96 were: -3.1 [-5.1-0.5] vs -7.6 [-15.2 to -3.6], respectively. Cystatin C-based eGFR remained stable through Wk 96 (median [IQR]: -2.8 [-7.4-8.9 mL/min/1.73 m(2)). Actual GFR assessment using CLiohexol (n=14) was unaffected over 24 Wks (median at baseline: 82.5, median changes from baseline at Wks 2, 4, and 24: 1.6, 7.0, -4.1 mL/min, respectively). Three renal discontinuations occurred (two worsening CrCl and one proteinuria/hematuria); none had proximal renal tubulopathy [PRT]. No patient had laboratory evidence of PRT (>1 confirmed renal laboratory abnormalities [increase in serum Cr≥0.4 mg/dL, ≥2-grade increase in proteinuria,≥1-grade increase in normoglycemic glycosuria or hypophosphatemia]). CONCLUSIONS: In HIV-infected patients with CrCl 50-89 mL/min, on ATV- or DRV-based regimen switching to COBI from RTV, demonstrated that COBI was well tolerated with no cases of PRT through 96 Wks. The renal safety profile of COBI in patients with mild to moderate renal impairment was consistent with the long-term data in patients without renal impairment (CrCl≥70 mL/min) from the phase 3 studies of COBI-containing regimens.