Gilead Sciences, Inc. (Nasdaq: GILD) today announced that the European Commission has granted marketing authorization for once-daily Tybost™ (cobicistat 150 mg tablets), a pharmacokinetic enhancer that boosts blood levels of certain HIV medicines. Tybost is indicated as a boosting agent for the HIV protease inhibitors atazanavir 300 mg once daily and darunavir 800 mg once daily as part of antiretroviral combination therapy in adults with HIV-1 infection. Today’s approval allows for the marketing of Tybost in all 28 countries of the European Union (EU). “Gilead is pleased to offer HIV patients who rely on protease inhibitors a new boosting option to help facilitate once-daily dosing – an important factor in supporting treatment adherence,” said Norbert Bischofberger, PhD, Executive Vice President, Research and Development and Chief Scientific Officer, Gilead Sciences. The EU approval of Tybost is supported by 48-week data from a pivotal Phase 3 study (Study 114), which found that Tybost was non-inferior to ritonavir when administered with an antiretroviral regimen of atazanavir plus Truvada ® (emtricitabine 200 mg and tenofovir disoproxil (as fumarate) 245 mg) in HIV-infected treatment-naïve adults. Approval is also supported by pharmacokinetic data demonstrating that Tybost boosts blood levels of atazanavir and darunavir similar to ritonavir. Tybost should only be co-administered with atazanavir or darunavir. In Study 114, Tybost was well tolerated and most adverse events were mild to moderate. The most common adverse reactions (incidence greater than or equal to 10 percent, all grades) were jaundice, ocular icterus and nausea. Tybost is a component of Gilead’s Stribild ® (elvitegravir 150 mg/cobicistat 150 mg/emtricitabine 200 mg/tenofovir disoproxil (as fumarate) 245 mg), a once-daily complete single tablet regimen for the treatment of HIV-1 infection that was approved in the United States in August 2012 and in the European Union in May 2013. Gilead submitted a new drug application to the U.S. Food and Drug Administration (FDA) for Tybost as a single agent in June 2012 and received a Complete Response Letter in April 2013. Gilead is working on resubmitting the application to the FDA. Tybost is approved as a single agent in Canada. About Tybost Tybost is a cytochrome P450 3A (CYP3A) inhibitor. It boosts blood levels of atazanavir and darunavir by suppressing CYP3A, an enzyme that metabolizes these drugs in the body. Tybost acts only as a pharmacokinetic enhancer and has no antiviral activity.