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2021-12-24| Trials & Approvals

FDA Gives Emergency Approval to Merck’s COVID-19 Pill after Giving Similar Nod to Pfizer’s Tablets

by Joy Lin
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The FDA has given emergency use authorization (EUA) to Merck’s Covid-19 oral antiviral, molnupiravir, a day after the drug regulator greenlighted Pfizer’s Paxlovid, which consists of nirmatrelvir and ritonavir tablets. Both treatments cover adults with mild-to-moderate Covid-19, who are at high risk for progression to severe disease. 

Molnupiravir is not recommended for patients younger than 18 because it may affect bone and cartilage growth. In comparison, Paxlovid’s coverage includes pediatric patients aged 12 and older. Both treatments are not recommended for prevention of Covid-19, as well as for hospitalized patients, due to the lack of efficacy data available. 

The FDA has warned that both antivirals are not substitutes for vaccination for individuals who are recommended the shots. 

30%, Not 50%

 

Molnupiravir is a ribonucleoside analog co-developed by Merck and Ridgeback Biotherapeutics. It works by inserting itself into the virus’ genetic code, introducing tiny errors that prevent the virus from replicating. It’s been shown to work across RNA viruses including SARS-CoV-2, which causes Covid-19. 

More recent research has shown that the pill is 30% effective at preventing hospitalization and death from Covid-19, if taken within five days of the onset of symptoms. That’s lower than a previous figure of 50% announced in October. 

Merck has expressed optimism that molnupiravir remains effective against the highly-mutated Omicron variant, as the drug inhibits viral mechanisms not involving the spike protein, which vaccines primarily target. The company has said it is currently evaluating the efficacy of molnupiravir against the variant. 

Molnupiravir is given as four 200 mg capsules taken orally every 12 hours for five days, for a total of 40 capsules. It is not authorized for use after five consecutive days. 

The emergency approval of molnupiravir is based on results from MOVe-OUT, a clinical trial that studied the drug in unvaccinated, non-hospitalized patients aged 18 and older with mild-to-moderate Covid-19 at high risk of progression to severe disease. The results showed that of the 709 patients treated with molnupiravir, 6.8% were hospitalized or died, compared to 9.7% of the 699 patients who received the placebo. 

Side effects observed in the trial included diarrhea, nausea and dizziness. 

Paxlovid, First Authorized Oral Antiviral

 

Pfizer’s Paxlovid was first to receive the EUA from the FDA for an oral antiviral treatment, snatching first place from under Merck. 

Paxlovid is a combination of two antiretrovirals, nirmatrelvir and ritonavir. Nirmatrelvir blocks activity of the 3CL protease, an essential enzyme for replication, in SARS-CoV-2. When ritonavir, a protease inhibitor, is given alongside nirmatrelvir, it slows the breakdown of the latter, allowing nirmatrelvir to exert its effect in the body for a longer period of time. 

Pfizer has said that Paxlovid works against multiple Covid-19 variants, including the Omicron variant, as the drug inhibits replication and not the spike protein. 

A dose of Paxlovid consists of two tablets of nirmatrelvir and one tablet of ritonavir. The three tablets are taken together by mouth twice daily for not more than five consecutive days, for a total of 30 tablets.  

The EUA for Paxlovid was based on results from EPIC-HR, a clinical trial studying Paxlovid for the treatment of non-hospitalized adults with Covid-19 symptoms, who have not been vaccinated against Covid-19 and have not been infected with the virus before. The results showed that Paxlovid significantly reduced the rate of hospitalization and death from Covid-19 by 88% compared to the placebo group. 0.8% of 1039 patients receiving Paxlovid were hospitalized or died, compared to 6% of the 1046 patients who received the placebo. 

Possible side effects of Paxlovid include impaired sense of taste, diarrhea, high blood pressure, and muscle aches. The FDA has cautioned that ritonavir may cause liver damage, so it may not be recommended for people with liver diseases or abnormalities.

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