SciCheck Digest: Neither Merck’s Molnupiravir nor Pfizer’s Paxlovid are similar to Ivermectin in any way


Merck, Pfizer COVID-19 Antivirals Different From Ivermectin

By Jessica McDonald

Posted on October 15, 2021

SciCheck Digest

Merck and Pfizer are each developing a new oral antiviral drug that might prevent or treat COVID-19. The pills are very different from the antiparasitic medication ivermectin, contrary to claims online that they are “suspiciously similar” or that the companies are “repackaging” ivermectin in a ploy to increase profits.

On Sept. 27, Pfizer said that it was launching a late-phase clinical trial to test whether, in combination with another drug, its oral COVID-19 antiviral can prevent infection with the coronavirus. Dubbed PF-07321332, the investigational medication is a protease inhibitor that blocks a key enzyme the SARS-CoV-2 virus needs to replicate itself.

The company previously started phase 2/3 trials in July and August to test whether the drug combo works as a treatment in people with confirmed infection.

On Oct. 1, Merck and Ridgeback Biotherapeutics announced positive phase 3 trial interim results for their COVID-19 antiviral. Called molnupiravir, after Thor’s hammer, the pill reportedly cut the risk of hospitalization and death in people with mild to moderate COVID-19 by around 50% when given within five days of symptom onset, according to a press release

Molnupiravir is a nucleoside analog — a drug that messes up viral replication by tricking the virus into using the processed medication as one of its building blocks for its genetic code. It’s a kind of molecular bait-and-switch operation that leads the virus to incorporate so many errors during replication that it cannot survive and propagate. This is what’s known as “error catastrophe,” using a mechanism called “lethal mutagenesis.”

Although both drugs are novel, with news of these developments, people on social media are spreading the false notion that the pills are the same or “suspiciously similar” to ivermectin — an antiparasitic medication that has not been shown to be effective against COVID-19 — because, they claim, the pharma companies want to drive up profits. (For more on ivermectin, see SciCheck’s article “Ongoing Clinical Trials Will Decide Whether (or Not) Ivermectin Is Safe, Effective for COVID-19.”)

“In other news, Pfizer is testing Ivermectin, now renamed PF-07321332, to help with Covid. They have done this so they can make this drug more expensive than Ivermectin, despite the fact, they are the same drug,” wrote one Twitter user, sharing a Reuters article about Pfizer’s COVID-19 prevention trial.

That tweet was labeled as sarcasm by its author, but it was nevertheless shared in a screenshot on Instagram, with the sharer falsely claiming that Pfizer was actually “attempting to reverse engineer a version of ivermectin that can’t quite legally be called ivermectin.”

Some iterations of the claim incorrectly posit that Pfizer’s drug is “based on” ivermectin and that the two are essentially the same because both are protease inhibitors — something that has not been established, and even if true, doesn’t mean the drugs are similar, as we’ll explain. 

“Pfizer’s new oral antiviral is just a protease inhibitor just like Ivermectin,” reads one such Instagram post, shared by Idaho state Rep. Tammy Nichols. “They’re literally repackaging ivermectin to sell to the masses with a new name.”

That post uses the phrase “Pfizermectin,” which may have originated on the conservative satire website the Babylon Bee in a parody drug advertisement posted to YouTube earlier in September.

Similar claims have been made about Merck’s molnupiravir, which in a deal with the government will cost around $700 for each course of pills if it receives authorization.

“Looks like Merck is repackaging the ‘horse drug’ and making it much more expensive! It will be the ‘new’ treatment for C. in pill form,” reads one Facebook post, referring to ivermectin. “My guess is they changed the formula just a bit to rebrand and patent.”

New Antivirals Nothing Like Ivermectin

Neither of the investigational drugs are ivermectin, nor are they particularly similar, which is obvious when looking at the chemical formulas and structures of the compounds.

Whereas ivermectin is made of just three kinds of atoms — carbon, hydrogen and oxygen — Pfizer’s drug also contains chlorine, nitrogen and sulfur; Merck’s drug also contains nitrogen, and its molecular weight is less than half that of ivermectin. Structurally, too, the drugs bear no resemblance.

“Pfizer’s 3CL protease inhibitor is nothing like ivermectin,” Dr. David Boulware, an infectious disease specialist at the University of Minnesota, told us in an email.

As a result, there is no basis for claiming that either the Pfizer or Merck drugs are similar to ivermectin in any way.

Concerns about drug pricing are valid, but the notion that Pfizer and Merck’s investigational novel antivirals are based on or are rebranded versions of ivermectin to generate higher profits is completely bogus.

It’s worth noting that even if one or both of the drugs is effective and authorized for use against COVID-19, it will still be valuable to be vaccinated, as vaccination is the best and cheapest way to prevent serious illness — and if needed, the drugs can be used to provide even better outcomes.

Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate




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