Gilead Sciences is celebrating after regulators in the USA gave the green light to Stribild, the firm's four-drug HIV treatment.

The pill, previously called Quad, has been approved by the US Food and Drug Administration as a new once-a-day combination pill to treat HIV-1 in adults who have never been treated for infection. Stribild is made up of Gilead's investigational drugs elvitegravir and cobicistat combined with the two active ingredients in the firm's Truvada (emtricitabine and tenofovir).

The approval is not surprising given that in May, an FDA panel voted 13-1 in favour of the therapy. That backing was based on data from two Phase III studies which demonstrated that Quad is non-inferior to the Gilead's own big selling combo Atripla (efavirenz/tenofovir/emtricitabine) and a regimen containing ritonavir-boosted atazanavir plus Truvada after 48 weeks of therapy.

The FDA noted that like many other HIV drugs, Stribild’s label will have a boxed warning that it can cause a build-up of lactic acid in the blood and severe liver problems, both of which can be fatal. Gilead is also required to conduct additional studies to help further characterise the drug’s safety in women and children, how resistance develops to the combo and the possibility of interactions between Stribild and other drugs.

So good news for Gilead and analysts believe Stribild is bound to become a blockbuster but there is concern about the cost, which is expected to come in at around $28,500 per year. However, Gilead says it will establish a patient assistance programme for people without insurance and provide discounts to state AIDS projects.

Also Gilead has granted Indian manufacturing partners and the Medicines Patent Pool the right to develop generic versions of Stribild and distribute them to 100 developing countries. Applications are also pending in Australia, Canada and the European Union.