Gilead Sciences announced last week that that its new “Quad” regimen is as effective as Atripla for treating HIV, according to the 48-week results of their Phase 2 clinical trial.

The company also announced that cobicistat, a component of the Quad pill that is being tested independently as a booster for protease inhibitors, was as effective as Norvir (ritonavir) in a separate 48-week Phase 2 clinical trial.

Gilead scientists were positive about the clinical trial results.

“The advent of the single-tablet regimen helped advance the care of people living with HIV, but additional options are needed, particularly for those who experience side effects with existing drug combinations,” said Dr. Richard Elion, lead researcher for the Quad clinical trial, in a press release.

“These positive Phase 2 data suggest that the Quad could be an important new option for people with HIV,” he added.

The Quad regimen is a fixed-dose, single tablet consisting of cobicistat, elvitegravir, and Truvada (emtricitabine/tenofovir). Elvitegravir is a new integrase inhibitor, which is a relatively new class of antiretrovirals that also includes Isentress (raltegravir).

Atripla, which is also made by Gilead, is a fixed-dose, single tablet that combines Sustiva (efavirenz) and Truvada.

The study included participants who had never taken antiretrovirals before and had viral loads (amount of virus in the blood) of at least 5,000 copies per milliliter and CD4 (white blood cell) counts greater than 50 cells per microliter.

Results showed that after 48 weeks, 90 percent of patients in the Quad treatment group had achieved viral suppression (viral load less than 50 copies per milliliter of blood) compared to 83 percent of participants in the Atripla treatment group.

The total number of reported side effects was similar between the two groups. In both cases, the common side effects were abnormal dreams or nightmares, fatigue, dizziness, diarrhea, drowsiness, headaches, anxiety, nausea, bloating, and rash.

However, researchers reported that fewer participants in the Quad treatment group experienced abnormal dreams or nightmares, dizziness, or anxiety.

Gilead also reported positive results for a separate study examining the use of cobicistat, a component of the Quad regimen, as a booster for protease inhibitor regimens.

Results from the 48-week cobicistat study showed that cobicistat-boosted Reyetaz (atazanavir) plus Truvada is as safe and effective as Norvir-boosted Reyataz plus Truvada.

Gilead is currently recruiting participants for a Phase 3 clinical trial to further study cobicistat as a protease inhibitor booster.

Gilead also announced that it has completed enrollment for a Phase 3 study of the Quad regimen versus Atripla, as well as for a separate Phase 3 study comparing Quad to a protease inhibitor-based antiretroviral regimen. Gilead expects to announce the results of both studies in 2011.

For more information, please see the Gilead website. To participate in the cobicistat Phase 3 clinical trial, please see the United States Clinical Trials registry.