12th Annual Conference of the British HIV Association 29 March–1 April 2006, Brighton, UK

SUCCESS DESPITE RESISTANCE: EMTRICITABINE INTENSIFICATION OF A TENOFOVIR, DIDANOSINE AND BOOSTED-ATAZANAVIR REGIMEN IN INDIVIDUALS WITH LOW-LEVEL VIROLOGICAL FAILURE

HIV Med 2006; 7(Suppl. 1):14 (abstract no. P14)

Laura Waters, Brian Gazzard and Mark Nelson
Chelsea and Westminster Hospital, London, UK

AIMS: Tenofovir (TFV) and didanosine (ddI) backbones lack potency when combined with a non-nucleoside in naïve subjects; evidence for boosted PI- based regimens is less clear. We describe treatment-experienced individuals on TFV/ddI/ritonavir-boosted-atazanavir (ATV/r) with low-level virological failure who added emtricitabine (FTC) despite previous lamivudine (3TC) failure.

METHODS: Using a prospectively collected database we identified all individuals who had FTC added to ATV/r-based HAART during virological failure; all were receiving TFV/ddI. Treatment history and resistance were analysed; viral loads (VLs) following addition of FTC were collected to 12 months.

RESULTS: Six subjects with detectable viraemia after a median of 12 months (range 6–12) TFV/ddI/ATV/r (four inadequate suppression, two rebound from undetectability) met study criteria. Patients had received a median of 6 (2–12) previous regimens. All were 3TC-experienced (4/6 had M184V, two had received 3TC as part of a non-suppressive regimen) and were fully susceptible to ATV (IAS database); 3/6 had mutations conferring intermediate resistance to TFV, 2/ 6 to ddI. VL at intensification ranged from 89 to 1035 copies/ml and all reached undetectability (<50 copies) within 6 months. 5/6 remain undetectable (median follow-up 10.5 months; range 6–12).

CONCLUSION: We demonstrated the successful use of FTC to intensify HAART in subjects with viraemia and a history of 3TC resistance/failure. This may be due to residual activity of FTC despite M184V and/or increased susceptibility to TFV and/or reduced viral fitness with M184V. TFV/ddI/ATV/r may lack potency in drug-experienced patients.

2006-03-29
P14

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