The US Food and Drug Administration has approved a new once-a-day combination drug to treat the HIV-1 infection in adults who haven’t previously been treated for the disease.

The drug, known commercially as Stribild and produced by Gilead Sciences, contains the previously approved HIV drugs emtricitabine and tenofovir disoproxil fumarate as well as two new compounds, elvitegravir and cobicistat.

Whereas elvitegravir is an HIV integrase strand transfer inhibitor designed to interfere with an enzyme the HIV virus needs to multiply, cobicistat is a pharmacokinetic enhancer that inhibits an enzyme known to metabolise certain HIV drugs. The combination of emtricitabine and tenofovir disoproxil fumarate, known commercially as Truvada, has been approved since 2004.

FDA Center for Drug Evaluation and Research Office of Antimicrobial Products director Edward Cox praised the evolution of multi-pill regimens to single-pill regimens to treat HIV, and said; "New combination HIV drugs like Stribild help simplify treatment regimens."

Gilead Sciences chairman and chief executive officer John C Martin also welcomed the approval.

Martin said; "Therapies that address the individual needs of patients are critical to enhancing adherence and increasing the potential for treatment success, and we are proud to introduce a new single tablet regimen for the healthcare and patient communities."

The approval comes off the back of two clinical studies where 1,408 adult patients were given either Stribild or Atripla, an HIV drug containing Truvada and efavirenz, once daily, or Stribild or Truvada plus atazanavir and ritonavir once daily.

The results of the study demonstrated that between 88% and 90% of patients who received Stribild had an undetectable amount of HIV in their blood, compared with 84% of patients treated with Atripla and 87% of patients treated with Truvada ples atazanavir and ritonavir.

Stribild is the latest in a number of HIV-related products to receive FDA approval so far this year. The FDA had previously green-lit the first over-the-counter home-use HIV test kit, while approval was also awarded to the first medication for pre-exposure prophylaxis to reduce the risk of sexually acquired HIV infection in adults at high risk.