The U.S. Food and Drug Administration has rejected Gilead Sciences' application for approval of the HIV antiretrovirals elvitegravir and cobicistat for use as stand-alone drugs, but the reason was because of “deficiencies in documentation and validation of certain quality testing procedures and methods,” the company stated in a release. Gilead submitted new drug applications to the FDA for the drugs in June 2012. The FDA did not raise safety concerns about either drug.

Both cobicistat, which, like ritonavir, boosts the levels of other HIV medications, and the integrase inhibitor elvitegravir are already components of Gilead's once-daily, single-pill combination therapy Stribild (elvitegravir/cobicistat/emtricitabine/tenofovir), which the FDA approved in August of last year.

Elvitegravir needs to be taken once a day, boosted by cobicistat, and operates similarly to Isentress (raltegravir), which is dosed at twice a day.

The company stressed it is working with the FDA to address the agency's questions.

To read a Reuters story about the FDA rejection, click here.

To read the Gilead release, click here.