The US Food and Drug Administration (FDA) approved a second at-home drug treatment for coronavirus one day after the agency gave a green light to the first.

The FDA approved the antiviral pill manufactured by Merck & Company, used to treat mild-to-moderate COVID-19 in adults who are at most risk for severe disease, with the goal of keeping them out of a hospital.

The drug, Molnupiravir, is said to reduce hospitalizations and deaths by around 30%, based on clinical trials of adults with high-risk factors.

But, as with Pfizer's Paxlovid, the Merck drug has to be administered within a few days of symptoms to be effective.

There is concern that by the time some patients realize they have the virus and they get a prescription for either drug, the window of effectiveness will close.

And the Pfizer drug is considered the better option of the two.

Paxlovid was shown to be about three times as effective as Molnupiravir, and the Merck drug will come with a warning about possible side effects to unborn children when given to pregnant women.

An FDA panel gave pre-approval to the Merck drug last month but warned it should only be given to patients who fit in a narrowly-defined "high-risk" category of coronavirus.

Still, the arrival of the Merck drug should help ease the demand for the Pfizer drug, which, initially, is expected to be rationed to the parts of the US that are hardest hit by the virus.

The Merck and Pfizer drugs are expected to treat the omicron variant of the coronavirus which is now the dominant strain in the US./aa