not only HIV-1 protease but also the host's cytochrome P450 3A4 enzyme that metabolizes lopinavir (Kempf et al., 1997). Lopinavir/ritonavir in combination prolongs bioavailability of lopinavir in vivo (Sham et al., 1998). Lopinavir but not ritonavir showed antiviral effect against SARS-CoV, MERS-CoV,