The US Food and Drug Administration (US FDA) has accepted the Gilead Sciences' refiling of two New Drug Applications (NDA) for cobicistat, a pharmacoenhancing or “boosting” agent that increases blood levels of the protease inhibitors atazanavir and darunavir to enable once-daily dosing of these medicines in HIV therapy, and elvitegravir, an integrase inhibitor for the treatment of HIV-1 infection in treatment-experienced adults.

The FDA has set target review dates under the Prescription Drug User Fee Act (PDUFA) of October 3, 2014 for cobicistat and October 4, 2014 for elvitegravir.

Gilead submitted NDAs for cobicistat and elvitegravir in June 2012. In April 2013, the company received Complete Response Letters from the FDA. In its communications, the agency stated that it could not approve the cobicistat and elvitegravir applications in their current forms, citing deficiencies in documentation and validation of certain quality testing procedures and methods that were observed during inspections. Gilead has worked with the FDA to address the questions raised in the Complete Response Letters.

Cobicistat and elvitegravir are components of Gilead’s Stribild (elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/tenofovir disoproxil fumarate 300 mg), a once-daily single tablet regimen for the treatment of HIV-1 infection. Stribild was approved in the United States in August 2012.

Cobicistat is approved under the tradename Tybost and elvitegravir is approved under the tradename Vitekta in Europe, Canada and Australia.

Cobicistat is a cytochrome P450 3A (CYP3A) inhibitor. It boosts blood levels of the HIV protease inhibitors atazanavir and darunavir by suppressing CYP3A, an enzyme that metabolises these drugs in the body. Cobicistat acts only as a pharmacokinetic enhancer and has no antiviral activity.

Elvitegravir was licensed by Gilead from Japan Tobacco Inc. (JT) in March 2005. Under the terms of Gilead’s agreement with JT, Gilead has exclusive rights to develop and commercialise elvitegravir as a single agent in all countries of the world, excluding Japan, where JT retains rights.

Cobicistat and elvitegravir are investigational products in the United States and their safety and efficacy have not yet been established.