Merck’s Oral COVID-19 Antiviral Treatment Causes Quick Reduction in SARS-CoV-2

A study has found that individuals with early COVID-19 who were treated with an investigational oral antiviral agent saw a quick reduction in the infectious SARS-CoV-2 virus.

Merck (Kenilworth, NJ, USA) has announced preliminary results from Ridgeback Biotherapeutics’ (Miami, FL, USA) Phase 2a randomized, double-blind, placebo-controlled trial to evaluate the safety, tolerability, and efficacy to eliminate SARS-CoV-2 viral RNA of molnupiravir (EIDD-2801/MK-4482). The findings on one secondary objective from the Phase 2a study, showed a reduction in time (days) to negativity of infectious virus isolation in nasopharyngeal swabs from participants with symptomatic SARS-CoV-2 infection, as determined by isolation in Vero cell line culture.


Molnupiravir is an investigational, orally-bioavailable form of a potent ribonucleoside analog that inhibits the replication of multiple RNA viruses including SARS-CoV-2, the causative agent of COVID-19. Molnupiravir has been shown to be active in several models of SARS-CoV-2, including for prophylaxis, treatment, and prevention of transmission, as well as SARS-CoV-1 and MERS

In a multi-center US Phase 2a study, researchers enrolled 202 non-hospitalized adults who had signs or symptoms of COVID-19 within seven days and confirmed active SARS-CoV-2 infection. The primary efficacy objective was reduction in time to viral negativity measured by reverse transcriptase polymerase chain reaction (RT-PCR) analysis of nasopharyngeal swabs. Periodic samples were collected for virologic analysis. Of the 182 participants with an evaluable nasopharyngeal swab, 42% (78/182) showed detectable levels of cultured virus at baseline. The full study results remain blinded and will be shared at a later date, as they become available. Other Phase 2 and Phase 2/3 studies are underway.

The researchers have described findings from the secondary endpoint of reduction in time (days) to negativity of infectious virus isolation in nasopharyngeal swabs from participants with symptomatic SARS-CoV-2 infection, as determined by isolation in Vero cell line culture. At day 5, there was a reduction in positive viral culture in subjects who received molnupiravir (all doses) compared to placebo: 0% (0/47) for molnupiravir and 24% (6/25) for placebo. Of 202 treated participants, no safety signals have been identified and of the four serious adverse events reported, none were considered to be study drug related.

“We are very pleased to share our initial Phase 2 infectivity data at this important conference, which remains at the forefront for critical clinical scientific information in infectious diseases,” said Dr. Wendy Painter, Chief Medical Officer of Ridgeback Biotherapeutics. “At a time where there is unmet need for antiviral treatments against SARS-CoV-2, we are encouraged by these preliminary data.”

“The secondary objective findings in this study, of a quicker decrease in infectious virus among individuals with early COVID-19 treated with molnupiravir, are promising and if supported by additional studies, could have important public health implications, particularly as the SARS-CoV-2 virus continues to spread and evolve globally,” noted Dr. William Fischer, lead investigator of the EIDD-2801 2003 study and Associate Professor of Medicine, Division of Pulmonary Diseases and Critical Care Medicine at the University of North Carolina School of Medicine.

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