Tenofovir resistance – need for caution but not panic

Global epidemiology of drug resistance after failure of WHO recommended first-line regimens for adult HIV-1 infection: a multicentre retrospective cohort study.

TenoRes Study Group. Lancet Infect Dis. [1] 2016 Jan 28. pii: S1473-3099(15)00536-8. doi: 10.1016/S1473-3099(15)00536-8. [Epub ahead of print]

Background: Antiretroviral therapy (ART) is crucial for controlling HIV-1 infection through wide-scale treatment as prevention and pre-exposure prophylaxis (PrEP). Potent tenofovir disoproxil fumarate-containing regimens are increasingly used to treat and prevent HIV, although few data exist for frequency and risk factors of acquired drug resistance in regions hardest hit by the HIV pandemic. We aimed to do a global assessment of drug resistance after virological failure with first-line tenofovir-containing ART.

Methods: The TenoRes collaboration comprises adult HIV treatment cohorts and clinical trials of HIV drug resistance testing in Europe, Latin and North America, sub-Saharan Africa, and Asia. We extracted and harmonised data for patients undergoing genotypic resistance testing after virological failure with a first-line regimen containing tenofovir plus a cytosine analogue (lamivudine or emtricitabine) plus a non-nucleotide reverse-transcriptase inhibitor (NNRTI; efavirenz or nevirapine). We used an individual participant-level meta-analysis and multiple logistic regression to identify covariates associated with drug resistance. Our primary outcome was tenofovir resistance, defined as presence of K65R/N or K70E/G/Q mutations in the reverse transcriptase (RT) gene.

Findings: We included 1926 patients from 36 countries with treatment failure between 1998 and 2015. Prevalence of tenofovir resistance was highest in sub-Saharan Africa (370/654 [57%]). Pre-ART CD4 cell count was the covariate most strongly associated with the development of tenofovir resistance (odds ratio [OR] 1.50, 95% CI 1.27-1.77 for CD4 cell count <100 cells per µL). Use of lamivudine versus emtricitabine increased the risk of tenofovir resistance across regions (OR 1.48, 95% CI 1.20-1.82). Of 700 individuals with tenofovir resistance, 578 (83%) had cytosine analogue resistance (M184V/I mutation), 543 (78%) had major NNRTI resistance, and 457 (65%) had both. The mean plasma viral load at virological failure was similar in individuals with and without tenofovir resistance (145 700 copies per mL [SE 12 480] versus 133 900 copies per mL [SE 16 650; p=0.626]).

Interpretation: We recorded drug resistance in a high proportion of patients after virological failure on a tenofovir-containing first-line regimen across low-income and middle-income regions. Effective surveillance for transmission of drug resistance is crucial.

Abstract [1]  Full-text [free] access  [2]

Editor’s notes: Global surveillance for tenofovir (TDF) resistance is important at a time of expanding use of TDF-containing regimens for treatment and prevention. This collaborative analysis used data collated from several small studies in different settings. Overall, around one in three people who had failed on TDF-containing treatment had evidence of TDF resistance, although this frequency varied between 20% in Europe to almost 60% in Africa. Mutations associated with NNRTIs and lamivudine/emtricitabine resistance were more common overall and were present in most people with TDF resistance.

The regional variation probably reflects differences in clinical practice and study inclusion criteria. All European studies involved cohorts with frequent viral load monitoring, whereas half of the African cohorts had no routine viral load monitoring. All European studies included people with virologic failure but with low-level viraemia (viral load <1000 copies/ml) whereas almost all African studies included only people with viral load >1000 copies/ml.

While these data provide useful estimates of the frequency of drug resistance mutations in people with virologic failure on first-line ART, there should be caution about extrapolating beyond this. Reports from cohort studies with an accurate denominator of all people starting TDF-containing first-line ART would be useful to give more reliable estimates of overall incidence of acquired TDF resistance. Moreover, there remains a need for representative population-based surveillance for acquired and transmitted drug resistance. So far, global surveillance has detected limited evidence of transmitted TDF-associated mutations, but this needs to be monitored closely, especially in high incidence settings.

Africa [7], Asia [8], Europe [9], Latin America [10], Northern America [11]
Botswana [12], Brazil [13], Burkina Faso [14], Cameroon [15], Canada [16], Democratic Republic of the Congo [17], France [18], Germany [19], Hong Kong Special Administrative Region of China [20], India [21], Israel [22], Italy [23], Kenya [24], Luxembourg [25], Malawi [26], Mexico [27], Netherlands [28], Nigeria [29], Portugal [30], Senegal [31], Singapore [32], South Africa [33], Spain [34], Swaziland [35], Sweden [36], Switzerland [37], Thailand [38], Uganda [39], United Kingdom [40], United Republic of Tanzania [41], United States of America [42], Zambia [43], Zimbabwe [44]
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