Cobicistat, a new pharmacokinetic (PK) enhancer from Gilead Sciences, is set to unseat Abbott’s Norvir (ritonavir) as the only approved HIV treatment booster. It’s key in the newly approved Stribild tablet (a.k.a. the Quad). It will also be sold as a stand-alone drug for use with other HIV meds, along with plans to combine it in tablets with Prezista (darunavir) and Reyataz (atazanavir).

PK enhancers slow the rate at which certain HIV drugs are metabolized in the liver by enzymes. This helps boost the blood levels of the medications, making them easier to take and more effective against the virus.

Many protease inhibitors require boosting. So does elvitegravir, the integrase inhibitor in Stribild, which also contains tenofovir and emtricitabine.

Compared with Norvir, cobicistat has no activity against HIV and doesn’t block as many liver enzymes, meaning that it won’t likely have as many drug interactions.  It does, however, have many of the same side effects as Norvir.