Protease inhibitor
There are two types of protease present in SARS-CoV, the CL-like protease and the papain-like protease, which is important for cleaving the polyproteins and releasing the nonstructural proteins (NSP1–16), which carry out important functions in the CoV life cycle. Among protease inhibitors, lopinavir was the most inhibitor and saquinavir was the least powerful inhibitor of CoV protease.[13] In molecular dynamic studies, flap closing was observed when these inhibitors bound to the SARS-CoV 3CL (pro).[14] Hong Kong University researchers demonstrated anti-SARS-CoV action of lopinavir at concentration of 4 μg/ml in vitro against the HKU-39849 isolate.[15] Ritonavir boosting along with lopinavir is used in the management of HIV.[16] A clinical study at the same Hong Kong University suggests that even after adjustment for LDH level (possible confounder), a significant association was seen between lopinavir/ritonavir use and better outcome.[15] As per the current guidelines, lopinavir + ritonavir is the recommended protease inhibitor for the treatment of 2019-nCoV (weak recommendation).[17]