The search for orally ingested therapeutics caught attention recently after the successful but brief clinical trials of Merck's Molnupiravir and Pfizer's Paxlovid. Paxlovid refers to Nirmatrevil in the presence of Ritonavir. Nirmatrevil, i.e. PF-07321332, is a small molecule that binds to a particular region of the SARS-Cov-2 main protease, blocking proteolytic cleavage of some of the SARS-Cov-2 polyproteins , hence viral replication at an early stage of infection. The x-ray structure of Nirmatrelvir bound to the SARS-Cov-2 3CL protease, aka Mpro, is available at the Protein Data Bank, PDB ID 7SI9 . The molecule is a descendant of an earlier created molecule, PF-00835231 , created during the SARS-Cov-1 outbreak in 2003 . Nirmatrelvir's precursor is an injectable and was modified, turned into an orally ingested pill, which gained FDA EUA approval as Paxlovid in Nov 2021. However, the approval is for patients with high risk of hospitalization or death after infection. The inhibition of viral replication to avoid serious illness has a window of ~5 days post-infection, after that the virus has multiplied enough in the body that inhibition will not have an effect.