CYP3A4 and COVID-19: Lopinavir/ritonavir combination remains a treatment regimen for COVID-19 in many countries although no clinical benefit was observed in a small study.17 Importantly, lopinavir/ritonavir can cause QT prolongation and are CYP3A4 inhibitors,17,18 and cannot be used with major CYP3A4 substrates such as chloroquine.