Nirmatrelvir/Ritonavir

**Semantic type:** Pharmacologic Substance

**Definition:** A fixed combination of nirmatrelvir, an inhibitor of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) main protease (Mpro; 3C-like protease; 3CL protease; 3CLpro; nsp5 protease), and ritonavir, an inhibitor of cytochrome P450 3A4 (CYP3A4), that may be used to treat coronavirus disease 2019 (COVID-19). Upon oral administration of nirmatrelvir/ritonavir, nirmatrelvir selectively targets, binds to, and inhibits the activity of SARS-CoV-2 Mpro. This inhibits the proteolytic cleavage of viral polyproteins, thereby inhibiting the formation of viral proteins including helicase, single-stranded-RNA-binding protein, RNA-dependent RNA polymerase, 20-O-ribose methyltransferase, endoribonuclease and exoribonuclease. This prevents viral transcription and replication. Ritonavir inhibits CYP3A4-mediated metabolism of nirmatrelvir, thereby increasing the plasma concentration of nirmatrelvir.

**Synonyms:** - Paxlovid - Ritonavir/Nirmatrelvir - SARS-CoV-2 protease inhibitors: nirmatrelvir/ritonavir