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Merck’s Covid Treatment Pill: What to Know About Molnupiravir

Merck on Friday announced that its new pill to treat Covid-19 reduced the risk of hospitalization and death by about 50 percent. Merck plans to seek emergency authorization for the antiviral pills to be used in the United States.

Here’s what you need to know.

The pills are meant for people who are sick with Covid but are not in the hospital. Merck’s Phase 3 clinical trial enrolled only unvaccinated people who were considered high risk, such as older people or those with medical conditions like diabetes or heart disease. Initially, the drug might only be available for those people, but experts expect it to eventually become more widely available.

The pills are designed to be taken as soon as possible once a person shows symptoms of having Covid — a time when the virus is replicating rapidly and the immune system has not yet mounted a defense. In Merck’s trial, volunteers had to have shown symptoms within the past five days, and some researchers think the pills must be taken even earlier to be most effective.

Merck said the drug cut the risk of hospitalization or death in half. In the Phase 3 trial, 7 percent of volunteers in the group that received the drug were hospitalized, and none died. In the group that got a placebo, 14 percent were hospitalized or died.

The 50 percent efficacy is lower than monoclonal antibodies, the intravenous cocktail used to treat high-risk people with mild or moderate Covid. Studies have shown that those antibodies reduce hospitalizations and deaths by up to 85 percent among those patients.

But experts said the new antiviral pills will most likely have a bigger overall impact on Covid than the cumbersome antibodies, because the pills can reach more people.

Merck said on Friday that it plans to seek emergency authorization from the Food and Drug Administration as soon as possible. Regulators could then authorize the drug before the end of this year, if all goes well.

Dr. Anthony S. Fauci, President Biden’s top medical adviser for the coronavirus, said at a White House briefing on Friday that he could not give a specific timeline for approval.

“The F.D.A. will look at the data, and in their usual very efficient and effective way, will examine the data as quickly as they possibly can, and then it will be taken from there,” he said.

Merck expects to be able to make enough pills for 10 million people by the end of this year. The U.S. government has already ordered 1.7 million courses of treatment.

That is nowhere near enough for everyone in the United States who gets sick with Covid to receive the pills.

The federal government is paying about $700 per course of treatment. That is about one-third of the cost of a monoclonal antibody treatment. The plan is to make the pills free for Americans, like the Covid vaccines. Whether there are any out-of-pocket costs is likely to be determined after the pills are authorized for use by regulators.

Merck did not report any serious side effects among volunteers in its clinical trial. Any side effects, which typically involve mild complaints like headaches, can be hard to distinguish from feeling ill from Covid, researchers said.

Pfizer is developing a similar pill, as are Atea Pharmaceuticals and Roche. Results from their clinical trials are expected within the next few months. They are unlikely to be available for use until next year.

The regimen is familiar to anyone who has taken Tamiflu for the seasonal flu or an antibiotic for a urinary tract infection. People will need to get a prescription, which they’ll fill at a pharmacy. Patients will take four capsules twice a day for five days — in other words, 40 pills over the course of the treatment.

Antiviral pills are designed to block the virus from replicating.

Molnupiravir tricks the coronavirus into using the drug to try to replicate the virus’s genetic material. Once that process is underway, the drug inserts errors into the genetic code.

“If you create enough errors or you create errors in parts of the virus that are absolutely critical, the virus can’t replicate,” said Daria Hazuda, vice president of infectious disease and vaccine research at Merck.

Sheryl Gay Stolberg contributed reporting.