Bristol-Myers Squibb is to develop a once-a-day pill to treat HIV that combines the US major's Reyataz with Gilead Sciences's investigational treatment cobicistat.

The firms have signed a licensing deal which will see B-MS formulate, manufacture and sell a combination of its protease inhibitor blockbuster  Reyataz (atazanavir) and cobicistat, an experimental boosting agent that increases blood levels of certain HIV medicines to "potentially allow for one-pill once-daily dosing". Gilead is currently studying the combo in Phase II and III studies in HIV-1 treatment-naive patients.

Gilead will retain rights to cobicistat as a stand-alone product and for use in combination with other agents. It is a key component of the firm's experimental Quad, which along with another new treatment elvitegravir and two active ingredients in Gilead's Truvada (emtricitabine and tenofovir), are all formulated into a single, fixed-dose tablet.

Gilead's chief scientific officer Norbert Bischofberger said cobicistat "provides us with the potential to co-formulate with a variety of commercially-available HIV medicines that require boosting for optimal efficacy". His counterpart at B-MS, Elliott Sigal, said the combo "has the potential not only to help simplify HIV therapy but also to address an unmet medical need".

B-MS and Gilead already share revenues on the big-selling Atripla, which combines Truvada with the former's Sustiva (efavirenz).