Pfizer’s new trial drug is not ivermectin in disguise

A Facebook post falsely suggests that a potential new Covid-19 treatment from Pfizer is essentially the same as ivermectin. In fact the two drugs are structurally very different. 

The post shows a screenshot of a Pfizer press release announcing the trial of a new antiviral agent against SARS-CoV-2, alongside a screenshot of a paper about ivermectin published in the journal Future Virology. 

The post highlights sections of the texts, showing that the new Pfizer drug candidate is a “protease inhibitor” and that “Ivermectin was found as a blocker of viral replicase, protease and Human TMPRSS2”. 

The post’s caption says: “Guess what's in that Pfizer twice a day ‘covid medication’ they're cooking up? The mystical horse-worming paste they've been losing money on, but with a brand new shiny label that rakes in the dough.” 

But even if both drugs do have a protease inhibitor effect (slowing down the enzyme protease, which breaks down proteins), Pfizer’s new drug trial candidate and ivermectin are completely different chemical compounds. According to Dr Stephen Griffin, a virologist and Associate Professor at Leeds Institute of Medical Research, they are “extremely structurally different”. 

What is ivermectin?

Ivermectin is an anti-parasite medication which is sometimes used as a treatment for infections like scabies as well as some forms of rosacea.

Throughout the pandemic, there has been debate about the drug and speculation that it could be used to treat or prevent Covid-19. We have written more about this previously. At the time of writing the question is still a subject of research. The World Health Organisation and the European Medicines Agency have said that ivermectin should not be used in patients with COVID-19 except in the context of a clinical trial.

The Department of Health and Social Care has also previously confirmed to  Full Fact that based on the available data, it did not believe that there is sufficient evidence to prove that Ivermectin is a safe and effective treatment for Covid-19. 

There are lots of different protease inhibitors

Ivermectin has been used extensively in the past as an anti-parasite medication, where it causes paralysis and death of developing parasites.

Some studies, however, have looked for evidence that ivermectin might have an antiviral effect, and if so, through what mechanism. Some, such as the one in the Facebook post, have suggested that this could be through ivermectin’s inhibitory effect on the enzyme protease, which is a key enzyme for viral replication. 

There are also other suggested mechanisms for how ivermectin may kill some viruses. 

There are lots of medications currently in use that work by inhibiting these enzymes. These drugs are known as protease inhibitors, and include medications for HIV and Hepatitis C. 

Dr Griffin told Full Fact that ivermectin is “nothing like” Pfizer’s new trial drug in terms of structure. 

He said that it is “very, very much different”, and that the two drugs’ structures differ in size and other features, such as having different aromatic rings, side chains and polarity. 

We asked both Pfizer and Merck (which produces ivermectin) for comment.