If you’ve tested positive for COVID-19, you might be wondering if it’s necessary to take an antiviral medication, such as Paxlovid.

Pfizer’s Paxlovid (nirmatrelvir and ritonavir) gained full approval from the U.S. Food and Drug Administration (FDA) on May 25, 2023. 

Another drug, Lagevrio (molnupiravir), is authorized for emergency use by the FDA under an Emergency Use Authorization (EUA) — but does not have full approval.

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As noted on Pfizer's website, Paxlovid is intended for the treatment of mild to moderate COVID symptoms to prevent severe illness, hospitalization or death in high-risk individuals.

Paxlovid, which must be prescribed by a doctor, works best when taken within five days of a COVID diagnosis or when the first symptoms appear, according to Sean Marchese, a registered nurse at The Mesothelioma Center in Florida, who has a background in oncology clinical trials.

"Patients should take the medication as soon as possible if they know or suspect they might have COVID to ensure it is most effective," he told Fox News Digital.

For those who do not have significant risk factors for Paxlovid, Marchese said, "starting treatment as soon as possible is essential, even if you only have mild symptoms."

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Similar to some antibiotics, Paxlovid is offered on a "dose card" that allows you to punch out 30 pills during treatment, said Marchese. The standard treatment is three pills twice daily over five days. 

Some patients may require a second course of Paxlovid if they have a rebound or relapse of COVID-19.

For those who have had COVID for more than a week, Paxlovid may be less effective and could potentially be harmful, Marchese advised.

There is a higher risk of harm from taking Paxlovid for those who have organ damage, such as reduced kidney or liver function, according to Marchese. 

"Pediatric patients under 12 years of age or those weighing under 88 pounds should also avoid Paxlovid," he said.

People with cancer should discuss potential interactions between their prescribed medications and Paxlovid, the expert advised.

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"Some cancer medications may inhibit the effects of Paxlovid," Marchese said. 

"Conversely, treatment with Paxlovid may reduce the effectiveness of some cancer medications."

As Pfizer notes on its website, physicians should "consider the benefit of Paxlovid treatment in reducing hospitalization and death, and whether the risk of potential drug-drug interactions for an individual patient can be appropriately managed."

People with HIV-1 infections should consult their provider before taking Paxlovid, the expert said, as the medication could interfere with long-term HIV treatment. 

"Other interactions with Paxlovid include cholesterol-lowering statins, such as Lipitor," he warned.

Some patients report a "rebound" effect with Paxlovid, where they may test positive for COVID-19 after the course of treatment but show no symptoms, noted Marchese. 

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"In these cases, reinfection is unlikely, and hospitalization or severe disease is rare," he said.

Potential side effects of the antiviral medication include hives or rashes on the skin or trouble breathing. 

"Those with hypersensitivity disorder should be especially cautious and notify their providers immediately if they experience any side effects," noted Marchese.

Other potential side effects include diarrhea, increased blood pressure, muscle aches and nausea.

"Vaccination efforts continue to be the most effective guard against COVID-19," Marchese said. "People who have a higher risk of complications or immune deficiency, such as cancer patients, should stay vigilant with the COVID-19 vaccinations and their other recommended vaccines."

Paxlovid was originally offered for free by the U.S. government. But as of Dec. 15, 2023, it transitioned to commercial distribution, according to the Health & Human Services website. 

Pfizer also operates programs to ensure affordable access for patients.

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Fox News Digital reached out to Pfizer with the opportunity to provide additional comment.

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