When to switch to second-line ART in children?

HIV-1 drug resistance and second-line treatment in children randomized to switch at low versus higher RNA thresholds.

Harrison L, Melvin A, Fiscus S, Saidi Y, Nastouli E, Harper L, Compagnucci A, Babiker A, McKinney R, Gibb D, Tudor-Williams G; PENPACT-1 (PENTA 9PACTG 390) Study Team. J Acquir Immune Defic Syndr. 2015 Sep 1;70(1):42-53. doi: 10.1097/QAI.0000000000000671.

Background: The PENPACT-1 trial compared virologic thresholds to determine when to switch to second-line antiretroviral therapy (ART). Using PENPACT-1 data, we aimed to describe HIV-1 drug resistance accumulation on first-line ART by virologic threshold.

Methods: PENPACT-1 had a 2 x 2 factorial design, randomizing HIV-infected children to start protease inhibitor (PI) versus nonnucleoside reverse transcriptase inhibitor (NNRTI)-based ART, and switch at a 1000 copies/mL versus 30 000 copies/mL threshold. Switch criteria were not achieving the threshold by week 24, confirmed rebound above the threshold thereafter, or Center for Disease Control and Prevention stage C event. Resistance tests were performed on samples ≥1000 copies/mL before switch, resuppression, and at 4-years/trial end.

Results: Sixty-seven children started PI-based ART and were randomized to switch at 1000 copies/mL (PI-1000), 64 PIs and 30 000 copies/mL (PI-30 000), 67 NNRTIs and 1000 copies/mL (NNRTI-1000), and 65 NNRTI and 30 000 copies/mL (NNRTI-30 000). Ninety-four (36%) children reached the 1000 copies/mL switch criteria during 5-year follow-up. In 30 000 copies/mL threshold arms, median time from 1000 to 30 000 copies/mL switch criteria was 58 (PI) versus 80 (NNRTI) weeks (P = 0.81). In NNRTI-30 000, more nucleoside reverse transcriptase inhibitor (NRTI) resistance mutations accumulated than other groups. NNRTI mutations were selected before switching at 1000 copies/mL (23% NNRTI-1000, 27% NNRTI-30 000). Sixty-two children started abacavir + lamivudine, 166 lamivudine + zidovudine or stavudine, and 35 other NRTIs. The abacavir + lamivudine group acquired fewest NRTI mutations. Of 60 switched to second-line, 79% PI-1000, 63% PI-30 000, 64% NNRTI-1000, and 100% NNRTI-30 000 were <400 copies/mL 24 weeks later.

Conclusions: Children on first-line NNRTI-based ART who were randomized to switch at a higher virologic threshold developed the most resistance, yet resuppressed on second-line. An abacavir + lamivudine NRTI combination seemed protective against development of NRTI resistance.

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Editor’s notes: Paediatric guidelines recommend that children living with HIV initiate ART early in life. Therefore duration of treatment is likely to be for several decades in children. Children have tended to be maintained on failing therapies longer than adults due to limited treatment options, particularly in resource-limited settings.

The PENPACT-1 trial compared two HIV viral load thresholds, <1000 and <30 000 copies/ml, for switching to second-line ART among children taking non-nucleoside reverse transcriptase inhibitor (NNRTI) or protease inhibitor (PI)-based first-line regimens. As expected, children starting NNRTIs as their first-line regimen developed more NRTI mutations than children starting on boosted PIs. Importantly, children switching to second line ART at the higher viral load threshold were much more likely to develop resistance if they were taking NNRTI as their first line regimen than if they were taking boosted PIs. The study highlights the more “forgiving” nature of the PI drug class in terms of development of drug resistance. The main implication of this finding is that delayed switching on PI-based ART is a safe option in settings where future drug options are limited, as the risk of development of clinically significant PI or NRTI mutations is low. Interestingly, use of an abacavir + lamivudine nucleoside backbone resulted in fewer thymidine analogue mutations (TAMs) than use of lamivudine + zidovudine or stavudine backbone. This finding was based on analysis of non-randomised data, but supports the current WHO recommendations to use abacavir as the first-line drug of choice in the NRTI backbone.

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