Lopinavir is an antiviral HIV Protease Inhibitor. Lopinavir has insufficient bioavailability alone, so it is used in therapy in combination with Ritonavir, a HIV protease inhibitor, which inhibits cytochrome P450-3A4 (CYP3A4), a liver enzyme that normally metabolizes protease inhibitors. Lopinavir also has an ability to inhibit ZMPSTE24 (zinc metallopeptidase STE24).Lopinavir has been used as a ZMPSTE24 and human immunodeficiency virus protease inhibitor. Lopinavir is an antiviral HIV Protease Inhibitor. Lopinavir has insufficient bioavailability alone, so it is used in therapy in combination with Ritonavir, a HIV protease inhibitor, which inhibits cytochrome P450-3A4 (CYP3A4), a liver enzyme that normally metabolizes protease inhibitors. Lopinavir also has an ability to inhibit ZMPSTE24 (zinc metallopeptidase STE24). Lopinavir has been used as a ZMPSTE24 and human immunodeficiency virus protease inhibitor.