GlaxoSmithKline (GSK), the maker of Epzicom (abacavir plus lamivudine), has issued a statement responding to changes the AIDS Clinical Trials Group (ACTG) made last week to study A5202. As reported here, the ACTG decided to tell study participants with high pretreatment viral loads whether they had been taking either Epzicom or Truvada (tenofovir plus emtricitabine) and to offer Epzicom users the option of switching to other nucleoside reverse transcriptase inhibitor options. This was because patients receiving Epzicom who began the study with viral loads over 100,000 copies had a poorer treatment response than those taking a regimen containing Truvada.

A5202, a 1,600-person study that began enrolling in 2005, is comparing four popular treatment regimens in people who’ve never taken antiretrovirals before. The study is comparing Epzicom with Truvada in combination with either Sustiva (efavirenz) or Norvir (ritonavir)-boosted Reyataz (atazanavir).

GSK asserts that the lesser response to Epzicom seen in the A5202 study is uncharacteristic. “Data from six GSK studies with 2,595 patients show higher viral load reduction…than was seen in the ACTG study,” the company’s statement reads. “In addition, 48-week results from the recently reported HEAT study…showed treatment with Epzicom reduced viral load to the target at 24 weeks in 94 percent of patients, compared to 95 percent in the Truvada arm—a comparable level of effectiveness.”

GSK also makes the point that A5202 began before a blood test became available to identify, before treatment is started, the roughly 5 percent of people who will have a hypersensitivity reaction (HSR) to abacavir, one of the drugs contained in Epzicom. Because of this, GSK theorizes that a greater number of people receiving Epzicom had to stop treatment early because of an HSR and were therefore counted as a virologic failure, compared with those taking Truvada.

 “GSK does not believe the interim results of this single, ongoing study warrant a change to clinical practice,” the statement concludes. “Epzicom offers a potent, effective, and generally well-tolerated HIV treatment backbone for many patients with HIV.”