Pfizer’s Covid-19 Pill Is Authorized in U.S.

The FDA said the drug, named Paxlovid, worked safely and would be an important tool in reducing hospital admissions and death.

The pill arrives as the Omicron variant spreads across the U.S. Researchers expect antivirals like Paxlovid would be effective against the new strain because of the way they work, but are waiting for studies to confirm their suspicion.

Patrizia Cavazzoni, director of the FDA’s drug division, described the authorization as a major step forward in the fight against the coronavirus. “This authorization provides a new tool to combat Covid-19 at a crucial time in the pandemic as new variants emerge,” she said.

Paxlovid is expected to be available at pharmacies and hospitals in the coming days. Initial supplies will be limited, until Pfizer can ramp up production.

The U.S. will have more than 250,000 courses of treatment available in January, President Biden said.

“As Pfizer works to produce these treatments as quickly as possible, we will work closely with them and provide any resource needed, including using the Defense Production Act if warranted,” he said.

The U.S. government has agreed to pay $5.29 billion to purchase 10 million treatment courses that Pfizer will deliver by the end of next year. The drug will be free to patients, Mr. Biden has said.

Pfizer said it aims to make 120 million treatment courses next year, up from its previous projection of 80 million.

The pill’s key advantage over most existing treatments is that patients can easily take them at home, unlike antibody therapies or the antiviral Veklury that usually require administration at a clinic or hospital.

“This breakthrough therapy, which has been shown to significantly reduce hospitalizations and deaths and can be taken at home, will change the way we treat Covid-19,” said Pfizer Chief Executive Albert Bourla.

The pill is for the newly infected who are considered at high risk for severe disease, which the Centers for Disease Control and Prevention has said includes people 65 years old and above, or those who have an another medical condition like cancer, diabetes or a chronic lung disease.

Pfizer’s pill was found to be more effective than another Covid-19 pill, developed by Merck MRK 0.82% & Co. and Ridgeback Biotherapeutics LP, in separate studies. The Merck-Ridgeback pill is expected to receive FDA authorization soon.

Paxlovid’s launch puts Pfizer in position to have a commanding presence in the world’s response to the pandemic.

The company’s Covid-19 vaccine, called Comirnaty and developed with BioNTech SE, has become the preferred shot for many countries and is expected to total more than $36 billion in world-wide sales this year.

Paxlovid could reach $18 billion in sales next year, according to JPMorgan Chase & Co. analysts.

Pfizer has said laboratory tests indicate that Paxlovid could work against the Omicron variant, in part because the drug works differently than other therapies targeting the spike protein on the virus.

Researchers designed the pill to stop the coronavirus from spreading in people by blocking activity of a key enzyme, known as protease, which the virus needs to replicate.

The enzyme isn’t believed to be mutated in Omicron, which is why Pfizer and other researchers say the antiviral likely will work against Omicron.

The authorization comes after researchers found Paxlovid was safe and cut the risk of hospitalization or death by about 89% if people at high risk of severe Covid-19 took the pill within three days of diagnosis.

The treatment was also highly effective if begun within five days of symptoms, according to Pfizer.

Some researchers have raised safety concerns, because Paxlovid is taken with another drug. The second drug, called ritonavir, helps Paxlovid fight the virus longer, but can cause side effects when taken with certain widely used heart and cholesterol medicines.

Under the authorization, the FDA said Paxlovid shouldn’t be used with certain drugs for conditions including cancer, irregular heart rhythms and depression.

The FDA also recommended against giving Paxlovid to patients with severe kidney disease or liver impairment and said patients with moderate kidney issues should take a reduced dose. In patients with moderate renal impairment, a reduced Paxlovid dose is needed, it said.

European health regulators, who are reviewing Pfizer’s application for Paxlovid clearance, recently issued preliminary guidelines recommending that people don’t use it if they are pregnant or are trying to get pregnant, or if they are taking certain medicines or have severely reduced kidney or liver function.

Pfizer has said it expects doctors and pharmacists will find most of the drug interactions to be manageable.

Under the authorization, patients age 12 and older should begin a course of treatment within several days of symptoms emerging to prevent their cases from turning serious and requiring hospitalization.

People with a prescription would take two Paxlovid pills and one ritonavir pill twice a day for five days.

Pfizer has licensed Paxlovid’s formula so that generic drugmakers can make it for low- and middle-income countries.

Pfizer is also studying the drug in a separate study in adults at lower risk of developing severe disease, including vaccinated individuals.

—Andrew Restuccia contributed to this article.

Write to Jared S. Hopkins at jared.hopkins@wsj.com and Joseph Walker at joseph.walker@wsj.com