<p>This inhibits the main protease (Mpro) of the SARS-CoV-2. This main protease (Mpro) is also referred as 3C-like protease (3CLpro) or nsp5 protease. This inhibition of Mpro hampers the peptidomimetic activity of SARS-CoV-2. Ritonavir is an HIV-1 protease inhibitor but is not active against SARS-CoV-2 Mpro. Ritonavir inhibits the CYP3A mediated metabolism of Nirmatrelvir, resulting in increased plasma concentrations of Nirmatrelvir.</p>