The U.S. Food and Drug Administration (FDA) has approved Gilead Sciences’ Tybost (cobicistat) as a boosting agent to raise the drug levels of Reyataz (atazanavir) or Prezista (darunavir) in combination with other antiretrovirals to treat HIV. The drug is the second boosting agent to hit the market, after the widely used Norvir (ritonavir), which is manufactured by AbbVie.

The approval of the Reyataz and Tybost combination was based on a Phase II and III trial among people new to HIV treatment that compared the pair of drugs with Norvir–boosted Reyataz; each combo was given with Truvada (tenofovir/emtricitabine). The study found that the Tybost–containing regimen was as good as the regimen with Norvir.

The approval of the Prezista and Tybost pairing was based on a trial among HIV-negative individuals comparing how the participants’ bodies absorbed that combination with those of other people who took Prezista and Norvir.

According to Daniel S. Fierer, MD, an assistant professor of infectious diseases at Mount Sinai Hospital in New York City, “the real value” of this approval “will come with the coformulation of [Tybost] with these two protease inhibitors, eliminating one large pill from the regimen of patients on these PIs that previously could only be boosted with [Norvir].”