This substance, also known as PF-07321332, is a protease inhibitor
. Its target is the 3C-like protease, the enzyme produced in coronaviruses infected cells, which cleaves the coronavirus polyprotein at well defined positions, to release individual proteins, rather like cutting a string of sausages. These are non-structural proteins such as enzymes used by the virus in the infection cycle within body cells.
This is similar to protease inhibitor drugs which have proved so effective in treating infections by HIV.
The nitrile (cyano) group
of the paxlovid molecule - its 'warhead' - forms a covalent bond with the amino acid cysteine in the active site of the protease enzyme and other groups block its substrate-binding pocket, preventing its usual hydrolytic action.
The pyrrolidone group
is said to simulate the R group of the amino acid glutamine, which marks the sites of action of the protease.
Paxlovid can be taken orally, whereas previous compounds needed to be to be administered intravenously.
Interim results showed that combining the drug with ritonavir
reduced the risk of hospitalization or death for adults with mild to moderate COVID-19 but at high risk of severe disease by 89% compared with a placebo.
Its maker Pfizer plans to submit the data as part of its ongoing rolling submission to the U.S. FDA for Emergency Use Authorization (EUA).