Pharmaceutical company Merck has said it will seek authorisation in the US for an oral drug for Covid-19, after the pill showed "compelling results" in a clinical trial.

The experimental drug, molnupiravir, significantly reduced the risk of hospitalisation or death when administered to high-risk patients early in the disease, Merck and its partner Ridgeback Biotherapeutics said in a statement.

"At the interim analysis, 7.3% of patients who received molnupiravir were hospitalised through Day 29, compared with 14.1% of placebo-treated patients who were hospitalised or died."

There were no deaths in the molnupiravir group.

The phase three clinical trial evaluated data from 775 patients with laboratory-confirmed mild to moderate Covid.

"Merck plans to seek emergency use authorisation in the US as soon as possible and to submit applications to regulatory agencies worldwide," the companies said.

Due to the positive results, the Phase 3 trial is being stopped early at the recommendation of outside monitors.

"This is going to change the dialogue around how to manage Covid-19," said Robert Davis, Merck's chief executive officer.

If authorised, molnupiravir, which is designed to introduce errors into the genetic code of the virus, would be the first oral antiviral medication for Covid-19.

Rivals including Pfizer Inc and Swiss pharmaceutical Roche Holding AG are racing to develop an easy-to-administer antiviral pill for Covid.

However, so far, only antibody cocktails, which have to be given intravenously, are approved for treating non-hospitalised Covid patients.

Patients had mild-to-moderate Covid

"Antiviral treatments that can be taken at home to keep people with Covid-19 out of the hospital are critically needed," said Wendy Holman, Ridgeback's CEO.

In the trial, which enrolled patients around the world, molnupiravir was taken every 12 hours for five days.

The study enrolled patients with laboratory-confirmed mild-to-moderate Covid-19, who had symptoms for no more than five days.

All patients had at least one risk factor associated with poor disease outcome, such as obesity or older age.

Merck said viral sequencing done so far shows molnupiravir is effective against all variants of the coronavirus, including highly transmissible Delta.

The company said rates of adverse events were similar for both molnupiravir and placebo patients, but did not give details of the side effects.

Merck has said data shows molnupiravir is not capable of inducing genetic changes in human cells, but men enrolled in its trials have to abstain from heterosexual intercourse or agree to use contraception.

Women of child-bearing age cannot be pregnant and also have to use birth control.

Merck said it expects to produce 10 million courses of the treatment by the end of 2021, with more doses coming next year.

The company has a US government contract to supply 1.7m courses of molnupiravir at a price of $700 (€603) per course.

Mr Davis said Merck has similar agreements with other governments worldwide, and is in talks with more.

The company said it plans to implement a tiered pricing approach based on country income criteria.

Merck has also agreed to license the drug to several India-based generic drug makers, which would be able to supply the treatment to low and middle-income countries.