Pfizer’s COVID-19 treatment, Paxlovid, has received emergency use authorization (EUA) by the FDA. The drug, which can be taken orally in the form of a pill, is authorized for the treatment of mild-to-moderate COVID-19 in adults and pediatric patients over 12. Eligible patients need to have a positive COVID-19 test and be at high risk for progression to severe COVID-19, including hospitalization or death. Paxlovid is available by prescription only and is recommended to be started as soon as possible after diagnosis of COVID-19 and within five days of symptom onset.

“Today’s authorization introduces the first treatment for COVID-19 that is in the form of a pill that is taken orally—a major step forward in the fight against this global pandemic,” said Patrizia Cavazzoni, MD, director of the FDA’s Center for Drug Evaluation and Research. “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.”

Paxlovid consists of two drugs—nirmatrelvir and ritonavir. Nirmatrelvir blocks the activity of the SARS-CoV-2-3CL protease, an enzyme required for viral replication. Co-administration with ritonavir, a protease inhibitor, slows the breakdown of nirmatrelvir so that it remains active in the body for longer periods of time at higher concentrations.

Pfizer noted on their website that nirmatrelvir has shown in vitro antiviral activity against multiple variants of concerns (i.e., alpha, beta, delta, gamma, lambda, and mu). In addition, they asserted, “Nirmatrelvir potently inhibited the 3CL protease associated with Omicron in an in vitro biochemical assay.”

Paxlovid is administered as three tablets (two tablets of nirmatrelvir and one tablet of ritonavir) taken together orally twice daily for five days, for a total of 30 tablets.

The primary data supporting the EUA for Paxlovid are from EPIC-HR, a randomized, double-blind, placebo-controlled clinical trial studying Paxlovid for the treatment of non-hospitalized symptomatic adults with a laboratory-confirmed diagnosis of SARS-CoV-2 infection. All patients had not received a COVID-19 vaccine and had not been previously infected with COVID-19. The outcome measured was the proportion of people who were hospitalized due to COVID-19 or died due to any cause during 28 days of follow-up.

Paxlovid significantly reduced the proportion of people with COVID-19 related hospitalization or death from any cause by 88% compared to the placebo group (1,039 patients received Paxlovid, and 1,046 patients received placebo). The results showed that 0.8% who received Paxlovid were hospitalized or died during 28 days of follow-up compared to 6% of the patients who received placebo.

Possible side effects of Paxlovid are impaired sense of taste, diarrhea, high blood pressure, and muscle aches. The FDA emphasized that Paxlovid is not a substitute for vaccination in individuals for whom COVID-19 vaccination and a booster dose are recommended and urges the public to get vaccinated and receive a booster if eligible.

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