Definition

A fixed combination of atazanavir, a human immunodeficiency virus type 1 (HIV-1) protease inhibitor, and ritonavir, a cytochrome P450 3A4 (CYP3A4) inhibitor, that may be used to treat HIV-1 infection. Upon oral administration of atazanavir/ritonavir, atazanavir selectively binds to the active site of HIV-1 protease and inhibits the proteolytic cleavage of viral Gag and Gag-Pol polyproteins in HIV-infected cells. This inhibition leads to the production of immature, non-infectious viral proteins that are unable to form mature virions. Ritonavir inhibits CYP3A4, thereby limiting the metabolism of atazanavir, which is a CYP3A4 substrate, and increasing its systemic exposure. This leads to an increased concentration and half-life of atazanavir as compared to the administration of atazanavir without ritonavir.