People taking an antiretroviral (ARV) combination including abacavir and lamivudine (typically used together as Epzicom) were just as likely to maintain an undetectable viral load over one year as people taking a combination including tenofovir and emtricitabine (typically used together as Truvada)—regardless of their initial HIV levels. These results, from a Canadian HIV cohort, were presented Thursday, July 22, at the XVIII International AIDS Conference (IAC), taking place July 18 to 23 in Vienna.

HIV experts have disagreed for a couple of years now over the appropriate place of abacavir/lamivudine in a person’s initial ARV regimen. Though British and European treatment guidelines recommend this nucleoside reverse transcriptase inhibitor (NRTI) duo for first-line therapy, U.S. Department of Health and Human Services (DHHS) guidelines list the combination as an alternative regimen. This is largely due to two lingering issue.

First there is concern regarding abacavir use and the potential increased risk of a heart attack. Though some studies have demonstrated a link, others have not.

Then there are efficacy concerns. In one study in particular, people with virus levels over 100,000 copies, who were taking a regimen including Epzicom, were less likely to get and keep their HIV under control, compared with people people taking a regimen containg Truvada.

To shed further light on the question of abacavir/lamivudine efficacy, Curtis Cooper, MD, from the University of Ottawa, and his colleagues from the Canadian Observational Cohort Collaboration (CANOC), reviewed the medical records of HIV-positive participants within the cohort. To be included in this analysis, participants’ abacavir/lamivudine- or tenofovir/emtricitabine-inclusive regimen must have been their first ARV combinations, they must have started treatment on or after January 1, 2000, and they must have had a CD4 and viral load test before starting therapy.

In all, 713 people were included in the study: 442 on abacavir/lamivudine and 271 on tenofovir/emtricitabine. These were combined with Sustiva (efavirenz), Viramune (nevirapine), Kaletra (lopinavir plus ritonavir) or Norvir (ritonavir)–boosted Reyataz (atazanavir). Cooper’s team analyzed the data in terms how well participants’ regimen suppressed HIV, when participants switched or stopped any part of their ARV regimen, and when they sopped taking their NRTIs specifically.

Cooper and his colleagues found no difference in efficacy between regimens of those taking abacavir/lamivudine and those taking tenofovir/emtricitabine. At 12 months, 93 percent of the participants taking an abacavir/lamivudine-inclusive regimen had fully suppressed virus, and 89 percent of those on a tenofovir/emtricitabine-inclusive regimen had suppressed virus. There were also no significant differences in terms of when someone stopped or switched any part of his or her ARV regimen.

There are weaknesses to the study, which Cooper acknowledged. These include the fact that the abacavir/lamivudine group included people who took it once daily as well as those who took it twice-daily, and while some took their pills separately (e.g., as Ziagen and Epivir), some took the fixed-dose combination of Epzicom. Also, the reasons that a person was put on a particular regimen, and the reasons for starting or stopping any of the drugs, were not available in the database. The CANOC study also does not address previous concerns about heart attack risks.

Lastly, because this study could only look backward at a group of people based on their treatment history (called a retrospective study), there could be confounding factors that wouldn’t have been present in a randomized controlled study, where people are randomly selected to take one treatment or another and followed closely.

Nevertheless, Cooper concluded his talk by stating that these data support including abacavir/lamivudine—Epzicom—as a reasonable first-line NRTI backbone choice.