Key TakeawaysMerck and Pfizer are both developing COVID antiviral pills.The drugs attack different parts of the virus and therefore work very differently.Pfizer’s pill has demonstrated greater efficacy rates compared to Merck’s drug.

Key Takeaways

Merck and Pfizer are both developing COVID antiviral pills.The drugs attack different parts of the virus and therefore work very differently.Pfizer’s pill has demonstrated greater efficacy rates compared to Merck’s drug.

As COVID-19 cases continue to surge, public health officials and researchers are looking for every tool to fight the virus. While vaccination should be the first line of defense, recently developed or repurposed antiviral medications may now offer treatment options as well.

Merck COVID-19 Treatment Pill: What You Need to Know

So how do these two pills compare? The Merck and Pfizer antivirals are comprised of very different pharmaceuticals, with extremely different efficacy rates.

Ramzi Yacoub, PharmD, chief pharmacy officer at SingleCare, told Verywell that while the drugs do essentially the same thing, they attack different parts of the virus.

“Merck’s polymerase inhibitor ‘tricks’ an enzyme so that it can’t be replicated properly and can’t survive,” Yacoub said. “Whereas, Pfizer’s Paxlovid is aprotease inhibitorthat blocks an enzyme that is needed for the coronavirus to replicate.”

How It Works

Merck

Merck’s molnupiravir was originally developed to combat viral Venezuelan equine encephalitis (VEE), a mosquito-borne disease. It was later found to also be effective against a virus in the coronavirus family,Middle East Respiratory Syndrome (MERS). The drug is considered a polymerase inhibitor since it targets ribonucleic acid polymerase.

As the RNA polymeraseduplicates, molnupiravir introduces fatal errors in the code, causing the virus to mutate to the point of death.

In the largest trial of the pill, molnupiravir was 30% effective at reducing hospitalization.Numbers climbed as high as 48% in smaller sample sizes in interim trials, but final numbers have settled.

Pfizer

Paxlovid combinestwo protease inhibitorsfor its virus attack. Ritonavir is an existing drug used to combat HIV. Nirmatrelvir is the brand name given to the experimental molecule PF-07321332, which was developed to specifically attack the protease of the COVID-19 virus.

While Nirmatrelvir attacks the protease of COVID-19, ritonavir attacks the enzymes that would take on Nirmatrelvir, operating as a team to slow the replication of the virus.

Pfizer Says Its COVID-19 Pill Will Be Effective Against Omicron. How Does It Work?

Daniel Chancellor, thought leadership director atInforma Pharma Intelligence, told Verywell that finding a unique molecule may be why Paxlovid has such strong results.

“This one drug has been specifically designed and tailored and optimized pharmacokinetically optimized for oral delivery against a specific protease for SARs-CoV-2,” Chancellor said. “This is a drug that’s designed for this particular virus, so that may be why the efficacy is so impressive.”

Omicron and Effectiveness

Who Should Take Them

Both drugs were tested on unvaccinated adults with at least one comorbidity such as obesity, age (over 65), diabetes, or heart conditions. The drugs need to be administered within five days of symptom onset for the maximum effect.

COVID-19 Treatments: What You Need to Know

Dosage

Molnupiravir’s full protocol is daunting—witha total course of 40 pillsover the course of five days. Each pill delivers 200 mg of the active ingredient. The pill is only recommended for adults over the age of 18 and should be administered within five days of symptoms appearing.

Paxlovidconsists of two pillsof the COVID-19 specific Nirmatrelvir, and one pill of an existing drug used to treat HIV, ritonavir. All three of the pills are taken twice daily for five days. Paxlovid has the best results when taken within three days of symptom onset.

Side Effects

While molnupiravir is shown to reduce hospitalizations and deaths from COVID-19, it’s not without its side effects.

Beyond any physical side effects, a small study published inThe Journal For Infectious Diseasesshowed that while it used mutagenesis to combat the virus, that same mutagenic effect could cause cancer or birth defects in developing fetuses.

The potential for birth defects may be part of the hold-up in receiving authorization. Concern about thepotential for birth defectsfor pregnant women and even their male partners was presented at the initial FDA approval presentation, but many are concerned that the drug may also open the door for further mutation of the SARS-CoV-2 virus itself.

“There is as well the viral variant generating potential, which is not a risk at the individual level, but as a risk at a global level,” Chancellor said. “With other treatments being available, such as antibodies, and such as Pfizer’s oral antiviral, it’s something that needs to be very, very carefully considered. [We need to balance] the individual benefits of the patient versus essentially changing the course of the pandemic.”

Pfizer has stated that side effects of Paxlovid are mostly mild but didn’t disclose what they are.

Side effects of ritonavir, the HIV drug used in conjunction with Nirmatrelvir, are established and include:

What This Means For You

The United Kingdom was the first country to authorized the use of molnupiravir. It will be available under the brand name Lagevrio. France hasdenied approvalfor the drug, citing low efficacy rates and high risks of mutagenicity.

Paxlovid earned authorization from the FDA one day before Merck. As of November 2021,Health and Human Serviceshad already secured 10 million courses of the drug protocol.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit ourcoronavirus news page.

5 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Kozlov M.Merck’s COVID pill loses its lustre: what that means for the pandemic.Nature.Ahmad B, Batool M, Ain Q ul, Kim MS, Choi S.Exploring the binding mechanism of pf-07321332 sars-cov-2 protease inhibitor through molecular dynamics and binding free energy simulations.IJMS. 2021;22(17):9124. doi. 10.3390/ijms22179124.Redd AD, Nardin A, Kared H, et al.Minimal cross-over between mutations associated with Omicron variant of SARS-CoV-2 and CD8+ T cell epitopes identified in COVID-19 convalescent individuals.bioRxiv. Published online December 9, 2021:2021.12.06.471446.Zhou S, Hill C, Sarkar S et al.β-d-N4-hydroxycytidine Inhibits SARS-CoV-2 Through Lethal Mutagenesis But Is Also Mutagenic To Mammalian Cells.J Infect Dis. 2021. doi:10.1093/infdis/jiab247Abbvie.Package insert - Norvir.

5 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Kozlov M.Merck’s COVID pill loses its lustre: what that means for the pandemic.Nature.Ahmad B, Batool M, Ain Q ul, Kim MS, Choi S.Exploring the binding mechanism of pf-07321332 sars-cov-2 protease inhibitor through molecular dynamics and binding free energy simulations.IJMS. 2021;22(17):9124. doi. 10.3390/ijms22179124.Redd AD, Nardin A, Kared H, et al.Minimal cross-over between mutations associated with Omicron variant of SARS-CoV-2 and CD8+ T cell epitopes identified in COVID-19 convalescent individuals.bioRxiv. Published online December 9, 2021:2021.12.06.471446.Zhou S, Hill C, Sarkar S et al.β-d-N4-hydroxycytidine Inhibits SARS-CoV-2 Through Lethal Mutagenesis But Is Also Mutagenic To Mammalian Cells.J Infect Dis. 2021. doi:10.1093/infdis/jiab247Abbvie.Package insert - Norvir.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Kozlov M.Merck’s COVID pill loses its lustre: what that means for the pandemic.Nature.Ahmad B, Batool M, Ain Q ul, Kim MS, Choi S.Exploring the binding mechanism of pf-07321332 sars-cov-2 protease inhibitor through molecular dynamics and binding free energy simulations.IJMS. 2021;22(17):9124. doi. 10.3390/ijms22179124.Redd AD, Nardin A, Kared H, et al.Minimal cross-over between mutations associated with Omicron variant of SARS-CoV-2 and CD8+ T cell epitopes identified in COVID-19 convalescent individuals.bioRxiv. Published online December 9, 2021:2021.12.06.471446.Zhou S, Hill C, Sarkar S et al.β-d-N4-hydroxycytidine Inhibits SARS-CoV-2 Through Lethal Mutagenesis But Is Also Mutagenic To Mammalian Cells.J Infect Dis. 2021. doi:10.1093/infdis/jiab247Abbvie.Package insert - Norvir.

Kozlov M.Merck’s COVID pill loses its lustre: what that means for the pandemic.Nature.

Ahmad B, Batool M, Ain Q ul, Kim MS, Choi S.Exploring the binding mechanism of pf-07321332 sars-cov-2 protease inhibitor through molecular dynamics and binding free energy simulations.IJMS. 2021;22(17):9124. doi. 10.3390/ijms22179124.

Redd AD, Nardin A, Kared H, et al.Minimal cross-over between mutations associated with Omicron variant of SARS-CoV-2 and CD8+ T cell epitopes identified in COVID-19 convalescent individuals.bioRxiv. Published online December 9, 2021:2021.12.06.471446.

Zhou S, Hill C, Sarkar S et al.β-d-N4-hydroxycytidine Inhibits SARS-CoV-2 Through Lethal Mutagenesis But Is Also Mutagenic To Mammalian Cells.J Infect Dis. 2021. doi:10.1093/infdis/jiab247

Abbvie.Package insert - Norvir.

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