An orally-administered antiviral drug initially developed to treat influenza can significantly decrease novel coronavirus levels in hamsters and is in the final stages of human trials, holding out promise of a pill to combat COVID-19, say researchers.

Scientists from the National Institutes of Health (NIH) in the US and the University of Plymouth in the UK found that MK-4482, also called Molnupiravir, was effective when provided up to 12 hours before or 12 hours after infection with SARS-CoV-2, the novel coronavirus that causes COVID-19.

The drug can also decrease damage it causes to lungs, states the study conducted on hamsters.

Published in the journal Nature Communications on April 16, it suggests that treatment with MK-4482 could potentially mitigate high-risk exposure to SARS-CoV-2 and might be used to treat established SARS-CoV-2 infection alone or in combination with other agents.

There are currently no drugs suitable for high-risk exposure use against SARS-CoV-2, the researchers said.

''In contrast to vaccines against SARS-CoV-2, we really don't have many drugs that are effective against the virus. This is an exciting result that identifies MK-4482 as an additional antiviral against SARS-CoV-2,” said Michael Jarvis, associate professor of Virology and Immunology at the University of Plymouth and a guest researcher at NIH.

“The drug, also called Molnupiravir, is in the final stages of human clinical trials in SARS-CoV-2 infected patients,” he added.

If human data shows a similar antiviral effect, it may be suitable for use as an orally administered pill following exposure to the virus, similar to the way Tamiflu is used for influenza, the researchers said.

“I think this additional control measure could prove to be really useful in the current pandemic,'' Jarvis added.

Though Remdesivir has already been approved by the US Food and Drug Administration under emergency use authorization (EUA) it must be provided intravenously, making its use primarily limited to clinical settings at later stages of the disease.

The research group developed a model last year which uses hamsters to mimic SARS-CoV-2 infection and mild disease in people.

The current research involved three groups of hamsters -- a pre-infection treatment group, a post-infection treatment group and an untreated control group.

The scientists administered MK-4482 orally in the two treatment groups every 12 hours for three days.

Their study found that the animals in each of the treatment groups had 100 times less infectious virus in their lungs than the control group.

Animals in the two treatment groups also had significantly fewer lesions or tissue damage in the lungs than the control group, according to the researchers. The researchers noted that MK-4482 has been shown to inhibit the replication of other related human coronaviruses, Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) in mouse models.

In their earlier research, the team determined the inhibitory effect of the drug on SARS-CoV-2 replication in human lung cells in the laboratory.

The treatment resulted in a significant decrease in SARS-CoV-2 replication when compared to no drug controls, they said.

The drug also demonstrated only minimal cellular toxicity.