As ritonavir is a known CYP3A4 inhibitor, their combination can be theoretically a more efficacious drug against COVID-19 as DRV/c, however, there is an increasing risk of drug interactions and severe side-effects (Hsu et al., 1998; Rittweger and Arastéh, 2007). Here, CYP3A4 is linked to COVID-19.