What do you know about that COVID-19 treatment Molnupiravir?


Molnupiravir is an antiviral pill that can be used in the treatment of adults with mild to moderate COVID-19 illness who are at high risk of serious illness. It should be taken within 5 days of the first symptom and only when other antiviral treatments are not available.

How does molnupiravir work? Get ready for some pharmacology! 😉

The SARS-CoV-2 virus is an RNA virus. This means it uses RNA for genetic material, instead of DNA. Molnupiravir is a drug that is metabolized by the body to D-N4-hydroxycytidine (NHC), a chemical that looks very similar to the building blocks of RNA. When the virus is making copies of itself, the NHC gets incorporated into that viral RNA and creates lots and lots of mutations. The virus becomes overwhelmed with bad mutations and is unable to make the proteins it needs to make copies of itself. This is called lethal mutagenesis.

Does it work?

Yeah…but not as good as other treatments that are available. Molnupiravir was granted emergency use authorization in the US in December 2021. The MOVe-OUT Trial (solidly good trial name) showed that molnupiravir reduced hospitalization rates and death by 30% compared to placebo for adults with mild to moderate COVID-19 who were at high risk of getting really sick. In the trial, the percentage of people who were hospitalized or died in the molnupiravir group was 6.8% compared to 9.7% in the placebo group. The absolute risk reduction is 2.9% (Not as impressive sounding as the relative risk reduction of 30%, right? Check out our earlier post on absolute and relative risks. This means that about 34 people would need to be treated with molnupiravir to prevent one death or hospitalization. Interestingly, the benefit was reduced in people who had previous COVID-19 infection, low viral loads, or had diabetes.

Remember, too, that real world efficacy is usually not as a good as trial data. So, while certainly better than nothing, this isn’t a slam dunk. Though we don’t have head-to-head comparisons, the reported efficacy for the monoclonal antibodies, remdesivir, and ritonavir-boosted nirmatrelvir (Paxlovid) were all higher. Because of this (and some of the concerns we will talk about below), molnupiravir is only recommended if none of the other treatments are available.

How do you take it?

Molnupiravir is a pill that is taken by mouth twice daily for 5 days. It must be started within 5 days of symptom onset. It is only for folks 18 years and older who do not need to be hospitalized for COVID-19 but are at high risk of getting really sick or dying (like people with cancer, diabetes, heart or lung disease, and weakened immune systems). You can see a more detailed list of high-risk conditions here.

It needs to be taken for the full 5 days. We don’t know if it is less effective if taken for a shorter amount of time or if a shorter course could cause the emergence of a variant that is resistant to molnupiravir. 😬

Are there side effects?

The most common side effects are diarrhea, dizziness, and nausea. 🤢

Because this drug works by creating mutations in the virus, there are theoretical concerns that molnupiravir use could lead to scary new variants. The FDA required the manufacture to monitor genomic databases for the emergence of new variants. They are keeping an eye on this one. 👀

What about pregnant people?

Molnupiravir is NOT recommended in pregnancy. People who could get pregnant should have a pregnancy test before starting this drug and should use contraception while taking the drug and for up to 4 days after finishing it. In animal studies, this medication was dangerous to the fetus. If there is nothing else available, a pregnant person could take it after talking with their doctor, if they are fully informed of the risk, and are ideally more than 10 weeks along in the pregnancy. Breastfeeding is also not recommended while taking molnupiravir.

Now that we have more treatment options, do we still need to get vaccinated?

YES! YES! YES! None of the available treatments are cures for COVID-19, and while the treatments reduce the risk of hospitalization and death, they do not eliminate that risk entirely. We also don’t know yet if the treatments reduce the risk of Long COVID (you better believe this is being studied). Vaccines are still the best tool we have to stop the spread and reduce infections, hospitalizations, and death.

Stay safe. Stay sane. Enjoy some clinical trial data.

Those Nerdy Girls


MOVe-OUT Trial

NIH Treatment Guidelines on Molnupiravir

Yale Medicine 9 Things to Know About Molnupiravir

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