Definition

A fixed combination of darunavir, a human immunodeficiency virus type 1 (HIV-1) protease nonpeptidic inhibitor, and ritonavir, a cytochrome P450 3A4 (CYP3A4) inhibitor, that may be used to treat HIV-1 infection. Upon oral administration of darunavir/ritonavir, darunavir selectively targets and binds to the active site of HIV-1 protease, and inhibits the dimerization and catalytic activity of HIV-1 protease. This 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, and prevents HIV replication. Ritonavir inhibits CYP3A4, thereby limiting the metabolism of darunavir, which is a CYP3A4 substrate. This leads to an increased concentration and half-life of darunavir as compared to the administration of darunavir without ritonavir.