Antiviral pills for COVID-19

Up to date, there are two oral antiviral pills with FDA emergency use authorization, Paxlovid from Pfizer, Molnupiravir from Merck. With these drugs, I believe that the COVID pandemic could end soon. What are those drugs? How does it work to treat COVID?

On December 22nd, 2021, the U.S. FDA issued an emergency use authorization (EUA) for Pfizer antiviral pills. Paxlovid could treat mild to moderate COVID-19 in adults and pediatric patients who are older than 12 years old and more than 40 kg. Additionally, Paxlovid could be prescribed and taken within 5 days of symptom onset. However, Paxlovid could not be utilized for the pre-exposure or post-exposure prevention of COVID-19 or any treatment for severe COVID-19. In the clinical trial, the result shows that Paxlovid could significantly reduce the proportion of people with COVID-19 induced hospitalized or died by 88%. Since we have known that Paxlovid could effectively treat COVID-19 within 5 days of symptom starting, we are interested in how Paxlovid works to treat COVID. One Paxlovid consists of 2 tablets of nirmatrelvir and 1 tablet of ritonavir and the patient should take these twice a day for 5 days. (30 tablets in total for one treatment). Nirmatrelvir in Paxlovid could inhibit a COVID protein to stop the virus from replicating, and ritonavir could enhance the stability of nirmatrelvir and help it to maintain at a high concentration in the body. Its potential side effects are impaired sense of taste, diarrhea, high blood pressure, and muscle aches. Furthermore, Paxlovid might have a significant drug interaction with certain drugs, and it would lead to HIV-1 drug resistance for those people who have uncontrolled or undiagnosed HIV-1 infection. Last, due to the potential damage in the liver and kidney, Paxlovid is not recommended for patients with severe kidney or severe liver impairment.

One day later(12/23/2021), the U.S. FDA issued a EUA for Merck’s Molnupiravir to treat mild to moderate COVID-19 in adults. Additionally, similar to Paxlovid, Molnupiravir should be prescribed and taken within 5 days of symptom onset. One important thing for Molnupiravir is that it can not be taken for patients who are younger than 18 years old because Molnupiravir might affect bone and cartilage growth. The mechanism to treat COVID-19 is that Molmupiravir could introduce errors into the COVID virus’ genetic code to prevent the virus from replicating. In the clinical trial, the result indicates that with Molnupiravir only 6.8% of patients were hospitalized or died compared to 9.7% of patients who received placebo. The treatment of Molnupiravir is to orally take 4 capsules (200 milligrams) twice a day for 5 days. (40 capsules in total) Its potential side effects are diarrhea, nausea, and dizziness. Moreover, from animal studies, Molnupiravir has been found to potentially cause fetal harm in pregnant women. Therefore, this drug is not recommended for use during pregnancy.

In conclusion, both Paxlovid and Molnupiravir could effectively prevent hospitalization or death, but these antiviral drugs could not be a substitute for vaccination or a booster shot. Please receive an FDA-approved COVID-19 vaccine and booster shot to maintain enough immune protection from COVID-19 including the omicron variant.


  1. the U.S. Food and Drug Administration

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Jason(Yen-Chun) Lu, All right reserved.

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