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McClatchy Washington Bureau
McClatchy Washington Bureau
National
Daniella Segura

How does Paxlovid work? Here’s what to know about the COVID antiviral medication

California Gov. Gavin Newsom was prescribed Paxlovid after he tested positive for COVID-19 over the weekend, his office announced.

“The Governor has also received a prescription for Paxlovid, the antiviral that has been proven effective against COVID-19, and will begin his 5-day regimen immediately,” the May 28 statement said.

The Food and Drug Administration first issued an emergency use authorization for Paxlovid in December.

“This authorization provides a new tool to combat COVID-19 at a crucial time in the pandemic as new variants emerge and promises to make antiviral treatment more accessible to patients who are at high risk for progression to severe COVID-19,” Dr. Patrizia Cavazzoni, director of the FDA’s Center for Drug Evaluation and Research, said at the time of the drug’s authorization.

When the drug was studied, researchers tried to test whether the drug prevented hospitalizations in patients at high risk of hospitalization, Dr. Tara Vijayan, who works in the division of infectious diseases at UCLA’s David Geffen School of Medicine, told McClatchy News.

“And what they found was that it actually reduced the risk of hospitalization by 89%,” she said.

Here are three things to know about Paxlovid.

Q. What is Paxlovid, and how does it work?

A. Paxlovid is an antiviral therapy meant to treat mild to moderate COVID-19, Dr. Michelle Hormozian, a clinical coordinator and pharmacist with the University of Southern California School of Pharmacy, told McClatchy News. It consists of two different oral antivirals: nirmatrelvir and ritonavir.

“One of the medications [nirmatrelvir], it’s actually a COVID protease inhibitor, and what that means is it basically prevents viral replication of COVID,” Hormozian said

The second medication, ritonavir, works to block the metabolism of the first drug so that the body can maintain sufficient levels of nirmatrelvir to work properly, Hormozian said.

COVID-19 positive patients who are prescribed Paxlovid will take it twice a day for five days, according to Hormozian.

Patients, depending on their medical history and current medications, will take one or two nirmatrelvir pills and one ritonavir pill, Vijayan said.

Some potential side effects of the drug may include an altered sense of taste, upset stomach or diarrhea, increased blood pressure or muscle aches, according to Hormozian.

Q. Who can take Paxlovid?

A. Paxlovid is meant to be taken by COVID-19 positive patients who are most at risk for hospitalization, Hormozian said. Patients should take Paxlovid within five days of their symptom onset.

“So, it’s not used for prevention. It’s not used for patients who might have been exposed but are not testing positive or those who are asymptomatic,” Hormozian said.

The drug is prescribed to those who are at higher risk of progressing into more severe COVID-19, Hormozian said. Physicians will look for other issues that put patients at a higher risk, including diabetes, chronic lung disease, like asthma, or being immunocompromised.

To be prescribed the medication, a physician will look over a patient’s medical history, including examining what medications the patient is taking, to determine if the drug is a good fit for the patient, according to Hormozian.

To take Paxlovid, a patient must be at least 12 years old and weigh more than 40 kilograms, or about 88 pounds, Hormozian said.

“But I would say younger individuals in general who are not taking any medications or don’t have any chronic medical conditions should not be taking Paxlovid,” Vijayan said.

Q. What about rebound COVID?

A. In some patients, physicians have seen rebound COVID after finishing their prescribed dosage of Paxlovid, Hormozian said.

“Some patients are testing negative after finishing Paxlovid, and then later on, around day eight, testing positive again,” Hormozian said.

Should a patient test positive after completing Paxlovid and feel symptomatic, they should not again be prescribed Paxlovid, Vijayan said.

“The primary goal of this medication is to prevent hospitalization,” Vijayan said. “It’s not to actually reduce the days of symptoms that you have.”

Patients testing positive again should isolate, though, Vijayan said.

Despite the potential for rebound COVID, Vijayan urges patients to consider Paxlovid.

“It’s a really good drug, and people should not avoid it if they are at high risk of hospitalization,” she said. “They shouldn’t avoid taking it because they’re worried about the rebound symptoms.”

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