The risk for acquired HIV drug resistance is low, and immediate initiation of antiretroviral therapy (ART) does not increase that risk substantially, according to results of a recent study published in AIDS.

In this cohort study, data from the HIV-CAUSAL Collaboration was used to identify the risk for clinically identified drug resistance after the following treatment approaches: immediate initiation of ART, initiation with CD4 T-cell counts <500 cells/mm3, or initiation with CD4 T-cell counts <350 cells/mm3. The researchers evaluated clinically identified acquired drug resistance up to 7 years after baseline (first period following 1999 that patients were AIDS-free and ART-free).

Of the 50,981 participants, 10% had CD4 T-cell counts >500 cells/mm3 at baseline, and 63% initiated ART over a follow-up of 204,914 person-years. At the time of ART initiation, median CD4 T-cell count was 270 cells/mm3, and time from baseline was a median of 5 months.

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Overall, the risk for acquired drug resistance was 2.7% at 7 years following baseline. The risk was modestly higher for immediate ART initiation (3.2%) and for initiation at CD4 <500 cells/mm3 (3.1%). For initiation at CD4 T-cell counts <350 cells/mm3, the risk for acquired resistance was 2.8%.

Among participants with a baseline between 2005 and 2015, the estimated 7-year risk for acquired resistance was 1.9% for immediate initiation, 1.9% for initiation at CD4 T-cell counts <500 cells/mm3, and 1.8% for initiation at CD4 T-cell count <350 cells/mm3.

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The study authors explained that, “the risk of acquired drug resistance after immediate ART initiation, the currently recommended strategy for ART initiation, is very small and not materially larger than if treatment is deferred. Therefore, it is unlikely that the benefits of immediate ART initiation will be compromised by development of acquired drug resistance in high-income countries and that immediate initiation will imply a substantial increase in need of second line treatments.”


Lodi S, Günthard HF, Dunn D, et al; HIV-CAUSAL Collaboration. Effect of immediate initiation of antiretroviral treatment on the risk of acquired HIV drug resistance [published online November 10, 2017]. AIDS. doi:10.1097/QAD.0000000000001692