Gilead Sciences' experimental Quad pill worked as well as Atripla (the tenofovir/emtricitabine/efavirenz coformulation) in a head-to-head trial of once-daily, all-in-one first-line regimens, researchers reported at CROI (abstract 58LB). The Quad is a combination pill containing the experimental integrase inhibitor elvitegravir, the novel boosting agent cobicistat (formerly GS 9350), tenofovir, and emtricitabine.

In a Phase II trial, 90% of participants in the Quad arm achieved a viral load below 50 copies/mL at 24 weeks, compared with 83% in the Atripla arm. The two coformulations produced equivalent CD4 cell gains, but the Quad was associated with fewer side effects, especially neuropsychological symptoms.

Gilead is also testing cobicistat as a stand-alone drug, a potential competitor for ritonavir (Norvir), currently the sole approved boosting agent, or pharmacoenhancer. In a 24-week analysis, 84% of treatment-naive participants receiving the protease inhibitor atazanavir (Reyataz) boosted with 150 mg cobicistat achieved undetectable viral load, compared with 86% of those receiving atazanavir boosted with 100 mg ritonavir. CD4 cell increases and overall adverse event rates were also similar.

In both trials, however, people taking cobicistat had higher serum creatinine levels and lower estimated glomerular filtration rate (eGFR), two indicators of possible kidney dysfunction. Presenter Calvin Cohen explained that prior studies of healthy HIV negative volunteers suggested that cobicistat may inhibit kidney tubular secretion, leading to elevated creatinine, but it does not appear to cause serious kidney toxicity. Since creatinine is one factor used to calculate eGFR, he said, cobicistat alters estimated but not actual glomerular filtration rate.

Gilead has announced that Phase III studies of both the Quad pill and cobicistat alone are expected to start by the middle of 2010; the company plans to request approval of the two in parallel, along with an elvitegravir/cobicistat coformulation.

Liz Highleyman (liz@black-rose.com) is a freelance medical writer based in San Francisco.