Washington DC - The US Food and Drug Administration on Thursday authorized a second anti-viral pill to treat Covid-19, just a day after authorizing the first antiviral pill for the coronavirus.

On Thursday, the FDA issued an emergency use authorization for Merck's (MRK) molnupiravir for the treatment of mild-to-moderate coronavirus disease.

The pill has been approved for use by adults with positive results of direct SARS-CoV-2 viral testing, and who are at high risk for progression to severe Covid-19, including hospitalization or death.

The pill is also approved for those for whom alternative Covid-19 treatment options authorized by the FDA are not accessible or clinically appropriate.

Molnupiravir is available by prescription only and should be initiated as soon as possible after diagnosis of Covid-19 and within five days of the onset of symptoms.

"Today's authorization provides an additional treatment option against the Covid-19 virus in the form of a pill that can be taken orally," said Patrizia Cavazzoni, director of the FDA's Center for Drug Evaluation and Research.

"As new variants of the virus continue to emerge, it is crucial to expand the country's arsenal of Covid-19 therapies using emergency use authorization, while continuing to generate additional data on their safety and effectiveness," she said.

The FDA authorized Pfizer's paxlovin pill for Covid-19 on Wednesday. Both pills may be taken orally at home, a breakthrough approval for healthcare providers as the US continues to fight the onslaught of the Delta variant as well as the highly contagious Omicron variant.

Earlier this week, the Centers for Disease Control and Prevention (CDC) released data saying the Omicron variant accounted for some 73% of US Covid-19 cases for the past week, and has now become the dominant strain in the country.

Molnupiravir is not authorized for use in patients younger than 18 years of age because it may affect bone and cartilage growth.

More than 800,000 people have died in the US in connection with Covid-19 infections since the pandemic began.