An effective, oral, direct-acting medicine is urgently needed to prevent transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and progression to severe coronavirus disease-2019 (COVID-19). 

The safety, tolerability, and antiviral efficacy of molnupiravir were evaluated in a Phase 2a clinical trial. The study enrolled 202 unvaccinated participants with SARS-CoV-2 infection having symptoms for <7 days. They were randomized 1:1 to receive 200 mg molnupiravir or placebo, and then 3:1 to receive molnupiravir (400 or 800 mg) or placebo, by oral route, in a BD dose for 5 days. RT-PCR was utilized to detect the antiviral activity for SARS-CoV-2 RNA in nasopharyngeal swabs. 

Cultured Vero cells were inoculated with nasopharyngeal samples to evaluate infectious virus and were detected by RT-PCR. 

The following observations were made-

• 800 mg molnupiravir group showed decreased Time to viral RNA clearance than the placebo group (median 14 and 15 days respectively). 
• Viral RNA clearance was achieved in more participants of the 800 mg molnupiravir group than the placebo group, 92.5% and 80.3% respectively, by the end of the study (4 weeks). 
• Infectious virus was detected in lesser swabs of the 800 mg molnupiravir group compared with the placebo group, 1.9% and 16.7% respectively, at day 3 of treatment. 
• Infectious virus was isolated from 0% participants receiving 400 or 800 mg molnupiravir, while from 11.1% of placebo recipients, at day 5 of treatment.  
• Molnupiravir demonstrated good tolerability, with comparable adverse events across all doses.

Source- Science Translational Medicine, 2021. DOI: 10.1126/scitranslmed.abl7430