Tenofovir and abacavir combination therapy: lessons learned from an urban clinic population

Regimens containing abacavir (ABC), tenofovir (TDF), and lamivudine (3TC) have recently been demonstrated to have high failure rates. This poses a clinical dilemma of how to manage patients currently being treated with other regimens containing tenofovir/abacavir. We evaluated the outcomes of tenofovir/abacavir regimens in our clinical practice through a retrospective review of 2655 charts. Two hundred patients (7%) were on a tenofovir/abacavir-containing regimen. Fifty-nine patients met the criteria for analysis and were grouped into three groups: (1) antiretroviral naïve, (2) virally suppressed patients switched to TDF/ABC, and (3) patients with failure of their first antiretroviral regimen. Rates of viral suppression in the naïve, switch, and first-failure groups were 95%, 86%, and 46%, respectively. In the first-failure group, viral suppression was 66% without and 18% with a preexisting M184V. A composite analysis of the groups revealed a success rate of 86% when the regimen contained zidovudine (ZDV) and 62% when it did not. No K65R mutations were noted. These findings support continued caution in the use of TDF/ABC in combination. However, these data suggest that this combination may be successfully used in selected situations such as in combination with ZDV. In patients already virally suppressed on a TDF/ABC-containing regimen, considerations include continuing the regimen or adding zidovudine, in the attempt to protect against the development of a K65R mutation and/or virologic failure, versus changing a stable regimen.