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Two years into the global pandemic, antiviral pills have emerged as a new therapeutic option. In late December of 2021, the FDA gave emergency use authorization (EUA) to two oral antiviral treatments for COVID-19: Paxlovid (Pfizer Inc.) and molnupiravir (Merk & Co). These hotly anticipated medications are intended for use in newly infected individuals who are at high risk of developing severe disease.
How do they work?
Paxlovid is a combination of two different medications, nirmatrelvir and ritonavir. Paxlovid blocks a key type of enzyme, called a protease, which cuts up SARS-CoV-2 (the virus which causes COVID-19) proteins into their active forms. When the protease is blocked, the virus can’t replicate (~90% of viral replication is inhibited), and the infection slows down, allowing the immune system to ramp up and fight the remaining virus.
Molnupiravir is incorporated into the RNA (the genetic blueprint) of SARS-CoV-2, resulting in defective genetic material and effectively stopping the virus from multiplying.
When and in whom can they be used?
Both pills are indicated for use in patients who are covid positive, symptomatic with mild to moderate disease, and at high risk of progression to severe disease. The treatments work best when started as soon as possible after a COVID-19 diagnosis and they must be started within five days of symptom onset. They are administered twice daily for five days.
Paxlovid: authorized for use in all adults and in children who are 12 years or older and weigh at least 88 pounds. There is a high potential for drug interactions (eg statins, blood thinners) with Paxlovid; make sure to inform your health care provider which other medications and over-the-counter supplements you are taking. Paxlovid may not be appropriate for individuals with liver disease, kidney disease, or those infected with the HIV virus
Molnupiravir: authorized for use in adults 18 or older. Cannot be used in pregnant or breastfeeding women. Molnupiravir is only approved for use in those “...for whom alternative COVID-19 treatment options authorized by the FDA are not accessible or clinically appropriate”.
How WELL do the treatments work?
In the studies cited by the FDA, Paxlovid reduced the rate of COVID-19 related hospital admission or death by ~88% and molnupiravir by ~ 33%.
What are the most common side effects?
Paxlovid: altered taste or loss of taste, diarrhea, high blood pressure, muscle aches
Molnupiravir: diarrhea, nausea, dizziness
* If you have recently been diagnosed with COVID-19, developed symptoms within the past five days, and think you may be eligible for one of the oral antiviral medications (eg you are at high risk of severe disease), please reach out to your health care provider.
