Molnupiravir serves as an inhibitor of RNA-dependent RNA polymerase and was earlier developed to treat influenza. It acts by increasing the frequency of viral RNA mutations to impair the replication of SARS-CoV-2 by a two-step mutagenesis mechanism, which describes its broad-spectrum antiviral activity. 

The first oral antiviral for COVID-19, molnupiravir, acquired regulatory approval from the Medicines and Healthcare Products Regulatory Agency (MHRA) in the UK in November 2021, for patients at risk of severe COVID-19 after testing positive for SARS-CoV-2 infection following lateral flow testing of a nasopharyngeal swab.

The potential activity of molnupiravir as an antiviral prophylactic against SARS-CoV-2 was first demonstrated in vitro in human airway epithelial cells and in vivo when it blocked SARS-CoV-2 transmission in ferrets. Phase 1 clinical trials have supported the safety and tolerability of molnupiravir and phase 2 clinical trials have shown that five days of oral molnupiravir therapy effectively eliminate nasopharyngeal SARS-CoV-2 in patients with early COVID-19. 

The recent approval of molnupiravir was based on a phase 2–3 clinical trial, which demonstrated molnupiravir to markedly reduce the risk of hospitalization or death in adults with mild or moderate COVID-19.

However, the role of molnupiravir in moderate to severe COVID-19 remains unknown and awaits further clinical trials. Also, the molnupiravir approval in the UK does not include pregnant women, women who intend to become pregnant, or women who are breastfeeding. 

The foremost regulatory approvals of molnupiravir and nirmatrelvir/ritonavir as the first oral antiviral drugs for COVID-19 have arrived at a vital time. The remdesivir use has been limited by the need for intravenous administration. Other drugs like four FDA-approved therapeutic neutralizing monoclonal antibodies, imdevimab, bamlanivimab, etesevimab, and casirivimab are costly and demand medically supervised intravenous administration. 

The effective, low-cost oral antiviral drugs that can be administered in the community at an early stage of SARS-CoV-2 infection are important for the control of COVID-19.

SOURCE- Med Sci Monit. 2022;28:e935952. Published 2022 Jan 1. doi:10.12659/MSM.935952