People taking an antiretroviral (ARV) combination including abacavir and lamivudine (typically used together as Epzicom) were no more likely to experience treatment failure, compared with 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 published in the September 1 issue of the Journal of Acquired Immune Deficiency Syndromes.

HIV experts have disagreed for a several 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 taking a regimen containing Truvada.

To shed further light on the question of abacavir/lamivudine efficacy, Darrell Tan, MD, from the University of Toronto, 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, 1,764 people were included in the study: 588 on abacavir/lamivudine and 1,176 on tenofovir/emtricitabine. These were combined with Sustiva (efavirenz), Viramune (nevirapine), Kaletra (lopinavir plus ritonavir) or Norvir (ritonavir)–boosted Reyataz (atazanavir). Tan’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 stopped taking their NRTIs specifically.

Tan and his colleagues did not find any statistically significant differences in the time to regimen failure, virologic failure, switching or stopping ARVs for non-virologic failure reasons, or virologic suppression according to the NRTIs used. In addition, there was no association between the NRTIs used and pre-treatment viral loads for any of the efficacy outcomes; results were similar for those who started treatment with viral loads in excess of 100,000 compared with those with pre-treatment viral loads below 100,000.

There are weaknesses to the study, which Tan and his colleagues acknowledged. These include the facts 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 (for example, 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, Tan’s group concluded by noting that these data support including abacavir/lamivudine—Epzicom—as a reasonable first-line NRTI backbone choice. “These results support the use of either NRTI backbone in the initial therapy of ART-naive patients and would support continuing [abacavir/lamivudine] as a ‘preferred’ NRTI option.”