- Molnupiravir, an oral antiviral pill authorized to treat COVID-19, has been available in the United States and other countries since December 2021.
- Molnupiravir and Paxlovid can reduce the severity of SARS-CoV-2 infection and reduce fatalities among people who are vulnerable to more severe COVID-19.
- New animal research suggests that molnupiravir efficiently blocked SARS-CoV-2 transmission
Two oral drugs, molnupiravir and paxlovid (nirmatrelvir/ritonavir), provide equivalent therapeutic benefit in preventing severe COVID-19 in animal models, but only molnupiravir efficiently blocked SARS-CoV-2 transmission when administered at a human effect size-equivalent dose, according to a study led by researchers at Georgia State University’s Center for Translational Antiviral Research in collaboration with the Emory University Institute for Drug Development.
The study published in the journal Nature Communications compared the efficacy of two licensed drugs, molnupiravir and paxlovid (nirmatrelvir/ritonavir), and the effects on SARS-CoV-2 transmission in dwarf hamster and ferret animal models. The researchers established correlations for animal and human dose levels, which can be complex.
Both drugs have received emergency use authorization, but therapeutic options against SARS-CoV-2 are underutilized. Effective treatments against SARS-CoV-2 are critical because extensive viral spread continues, despite the development of vaccines and antivirals. Also, the rise of new SARS-CoV-2 variants of concern that can escape preexisting immunity have reduced the possibility of rapidly ending the pandemic through large-scale vaccination campaigns.
This study affirms previous clinical analyses that early treatment of older adult patients at elevated risk of progression to severe COVID-19 with either paxlovid or molnupiravir will provide significant therapeutic benefit.
Richard Plemper, Ph.D., Director of the Center for Translational Antiviral Research at Georgia State University’s Institute for Biomedical Sciences
“We demonstrate in two animal model species, one rodent and one non-rodent, that infectious particle titers, but not viral RNA copy numbers, should be assessed to determine efficacy of a viral mutagen such as molnupiravir. Using reduction of viral RNA copies as biomarker available across all animal models and human patients, we demonstrate that molnupiravir, but not paxlovid, prevents all SARS-CoV-2 transmission when drugs were administered at human effect size-equivalent doses.”
The researchers compared both drugs in two animal models, the Roborovski dwarf hamster model for severe COVID-19-like lung infection and the ferret SARS-CoV-2 transmission model.
“Recent data has indicated another uptick in COVID-19 infections in a broad cross-section of the population. Antiviral drugs can play an important role in not only treating COVID-19 infection but also in controlling its transmission and spread,” said George Painter, Ph.D., Distinguished Professor of Pharmacology and Chemical Biology at Emory University School of Medicine, CEO of DRIVE (Drug Innovation Ventures at Emory) and director of the Emory Institute for Drug Development where molnupiravir was developed. “This collaborative study shows that molnupiravir treatment completely suppresses transmission at all dose levels tested. We look forward to continued studies to verify these exciting results.”
Additional authors of the study were Robert M. Cox and Carolin M. Lieber, co-first authors of the study from the Center for Translational Antiviral Research at Georgia State University’s Institute for Biomedical Sciences; Josef D. Wolf and Amirhossein Karimi of the Center for Translational Antiviral Research at Georgia State University’s Institute for Biomedical Sciences; Nicole A. P. Lieberman, Pavitra Roychoudhury and Alexander L. Greninger of the University of Washington; Zachary M. Sticher, Meghan K. Andrews, Rebecca E. Krueger, Michael G. Natchus and Alexander A. Kolykhalov of Emory University.
The study was funded by the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health.
Comparing molnupiravir and nirmatrelvir/ritonavir efficacy and the effects on SARS-CoV-2 transmission in animal models. Nature Communications, 7 August 2023. Summary: Therapeutic options against SARS-CoV-2 are underutilized. Two oral drugs, molnupiravir and paxlovid (nirmatrelvir/ritonavir), have received emergency use authorization. Initial trials suggested greater efficacy of paxlovid, but recent studies indicated comparable potency in older adults. Here, we compare both drugs in two animal models; the Roborovski dwarf hamster model for severe COVID-19-like lung infection and the ferret SARS-CoV-2 transmission model. Dwarf hamsters treated with either drug survive VOC omicron infection with equivalent lung titer reduction. Viral RNA copies in the upper respiratory tract of female ferrets receiving 1.25 mg/kg molnupiravir twice-daily are not significantly reduced, but infectious titers are lowered by >2 log orders and direct-contact transmission is stopped. Female ferrets dosed with 20 or 100 mg/kg nirmatrelvir/ritonavir twice-daily show 1–2 log order reduction of viral RNA copies and infectious titers, which correlates with low nirmatrelvir exposure in nasal turbinates. Virus replication resurges towards nirmatrelvir/ritonavir treatment end and virus transmits efficiently (20 mg/kg group) or partially (100 mg/kg group). Prophylactic treatment with 20 mg/kg nirmatrelvir/ritonavir does not prevent spread from infected ferrets, but prophylactic 5 mg/kg molnupiravir or 100 mg/kg nirmatrelvir/ritonavir block productive transmission. These data confirm reports of similar efficacy in older adults and inform on possible epidemiologic benefit of antiviral treatment.