Ivermectin: An In Vivo User Guide

The Anticlimactic Journey of a Repurposed Drug

Once again, a prescription drug has become a household name in the United States. Easy to pronounce and even easier to obtain from your local pharmacy (or livestock store), the antiparasitic ivermectin has recently undergone an astronomical increase in usage. Ivermectin’s pre-pandemic prescription rate of about 3,600 prescriptions per week spiked to over 88,000 prescriptions per week by mid-August 2021¹. However, this surge in usage is not associated with the treatment of parasitic diseases, but rather with attempts to treat the COVID-19 virus.

A handful of legitimate in vitro studies investigating ivermectin’s anti-viral properties have been largely overshadowed by the vast number of fraudulent or poorly conducted in vivo studies, causing public confusion over whether ivermectin can be considered a legitimate treatment for COVID-19. In the public eye, the debate was never a scientific one, but rather a giant log thrown onto the already blazing fire of contention in the American political system. Parties on either side of the COVID-19/ivermectin debate are equally passionate, but neither group seems to be backed by the scientific community. What exactly is ivermectin, and how did it rise to the forefront of the COVID-19 pandemic?

Ivermectin’s Origin Story

Discovered in 1975 by two scientists who were eventually awarded the 2015 Nobel Prize for their work, ivermectin is an internationally recognized and robust antiparasitic drug. Specifically, ivermectin is a highly efficacious broad-spectrum antinematode that damages nervous and muscular cells in parasitic worms. Ivermectin is formulated and dosed to treat parasitic infections in both humans and animals. If you have a four-legged friend at home, you are probably familiar with Heartgard; this is ivermectin for dogs, most commonly used to target roundworms and hookworms. In humans, ivermectin is prescribed to treat internal parasites that cause diseases such as river blindness and strongyloidiasis, two neglected tropical diseases that have infected hundreds of millions of people worldwide². Ivermectin is also used topically to treat infections caused by the parasites associated with lice and scabies.

Additionally, ivermectin is commonly used to treat parasitic infections in livestock. Ivermectin is an incredibly efficacious and safe drug (when dosed properly, as is the case with most drugs) that has saved countless lives and immeasurably elevated the state of global public health. Those who tout ivermectin as mere “horse paste” would be remiss to not recognize ivermectin’s life-saving global impact.

However, the lives saved by ivermectin are those that were given the drug at proper doses, to treat parasitic infections. You wouldn’t use a broad-spectrum antibiotic to treat a broken bone, and administering overdose-level quantities of antibiotic won’t magically cause your bone to heal. In a broader sense, just because a drug successfully treats one indication does not necessarily mean that it can treat other indications. While some drugs certainly can be successfully repurposed to treat indications other than the original target, repurposing a drug requires careful scientific experimentation and deliberation.

How Ivermectin Works

When new diseases arise, scientists look to see if existing drugs can be repurposed, because it’s easier, faster, and cheaper to repurpose an existing drug than it is to develop a new one. An existing drug’s known physiological and chemical properties are used as starting points for assessing if the drug could be used for other indications. In the case of ivermectin, scientists have a general understanding of its method of action against parasites. This knowledge can be leveraged to hypothesize if ivermectin could possibly treat non-parasitic targets.

In order to damage and ultimately kill parasitic worms, ivermectin targets cellular features that are specific to parasitic worms. While all cells have membranes with ion channels, there are types of ion channels that are present only in particular species. Parasitic worms are classified as “proteasome invertebrates”, a small taxonomic group that includes species such as jellyfish, sea urchins, crustaceans, and snails. These species are known to have cells that contain glutamate-gated chloride channels. This means that when glutamate, a naturally occurring amino acid, binds to such an ion channel, the ion channel opens and allows the passage of chloride ions over the cell membrane. The proper flow of ions over cell membranes is essential to physiological processes imperative to the survival of the cell and health of the overall organism.

While vertebrate cells have chloride channels that are gated by other ions, such as acetylcholine or glycine, glutamate-gated chloride channels have yet to be identified in vertebrates. This feature, that only invertebrates possess, can be exploited as a target in cases when invertebrate parasites infect vertebrates (i.e. when parasitic worms with glutamate-gated chloride channels infect humans without glutamate-gated chloride channels). When ivermectin is administered to an afflicted human or animal, ivermectin binds to the glutamate-gated chloride channels in the parasite’s cell membranes. This pushes open chloride channels, increasing the flow of chloride ions across the cell membrane, which ultimately paralyzes and kills the cell due to hyperpolarization of the cell membrane.

How could this method of action be applied to a viral target? Viruses don’t have cells, so ivermectin would not be able to directly “kill” a virus in the same way that it kills parasites. However, viruses cause disease in living organisms by infecting their cells. If ivermectin can bind to and block cellular receptors during viral infection in a mechanism similar to how ivermectin pushes open glutamate-gated chloride channels in parasitic cells, it certainly is possible from a physiological standpoint that ivermectin could have anti-viral properties.

In Vitro Triumphs

A 2012 study published in Biochemical Journal³outlines a series of experiments that demonstrate ivermectin’s anti-viral properties. The experiments described in the paper (authored by Kylie Wagstaff and colleagues at Monash University in Victoria, Australia) are follow-up experiments to a preliminary high-throughput screen⁴ used to identify molecules that inhibit viruses from entering the cell nucleus. In this preliminary screen, ivermectin was identified as one such viral protein nuclear import inhibitor (basically a long-winded way of saying that ivermectin successfully blocks viruses from entering the cell nucleus. This is important because when viruses enter cell nuclei, they override the nucleus’s machinery and force it to create more virus). The experiments detailed in the 2012 paper focus on ivermectin’s specificity towards nuclear import pathways, and the degree to which ivermectin can inhibit viral infection of cells grown in a lab.

The results of the 2012 study showed that ivermectin is a broad-spectrum inhibitor of a particular nuclear transport factor known as the importin alpha/beta1 heterodimer. The name of the transport factor isn’t important; what is important here is that “importins” (pun intended) are proteins that help move large molecules into the cell nucleus. The specific importin that ivermectin inhibits (importin alpha/beta1) is known to facilitate viral infection of cells. In order to assess how strongly ivermectin blocks viral infection via the importin alpha/beta1 heterodimer, cells were infected with both HIV-1 and dengue virus (in separate experiments). The infected cells were then divided into three groups: one treated with ivermectin, one treated another antiviral called mifepristone, and a “blank” control (the “blank” is used to measure levels of viral infection in untreated cells).

The results of these simple cell culture experiments were objectively clear: ivermectin significantly reduces viral replication in vitro. In the scientific industry, one experiment commonly used to measure viral infectivity is the plaque titer assay. In this experiment, cells are infected with virus and incubated for a defined length of time. Infectious viral particles eventually infect nearby cells and produce a visible blob, or a plaque, of infected cells. The more visible plaques, the more virus produced.

The scientists involved with this particular study used the plaque assay to assess how effective ivermectin was in inhibiting viral replication in cells. The cells that were infected with dengue virus and then treated with ivermectin showed almost no plaques, which means that ivermectin successfully blocked viral replication at the level of infection used in the study. The paper includes some great graphs showing the scientists’ work; you can check out their data here: Ivermectin is a specific inhibitor of importin α/β-mediated nuclear import able to inhibit replication of HIV-1 and dengue virus.

Dr. Wagstaff’s paper was a great first step in researching and establishing the potential of ivermectin’s antiviral properties. Since then, other cell culture experiments focused on ivermectin’s inhibition of viral activity have been performed. One such famous study is the Caly study⁵, authored by Leon Caly and colleagues at the Doherty Institute in Melbourne, Australia.

Ivermectin and COVID-19

The Caly study is a well-documented and clearly written paper that chronicles Dr. Caly’s experiments on ivermectin’s anti-viral properties. The paper validates the results described in the 2012 Biochemical Journal paper and dives further into trying to understand ivermectin’s antiviral method of action. What makes the Caly study special is that its objective was to directly assess ivermectin’s efficacy in inhibiting the replication of SARS-CoV-2, the virus that causes COVID-19.

The experiments outlined in the Caly study are similar in nature to those described in the 2012 Biochemical Journal article. Cells were infected with SARS-CoV-2 and treated with ivermectin. Cells treated with ivermectin were shown to have 5000 times less viral RNA compared to a “blank” control. Viral titer assays produce valuable data, but because things like counting plaques can be fairly subjective, the Caly study took the extra step to add a more quantitative piece of orthogonal data to support their findings: RT-PCR.

RNA was extracted from the COVID-infected/ivermectin-treated cells and then amplified and detected on RT-PCR, probing specifically for sequences found only in SARS-CoV-2 RNA. The PCR results showed anywhere from 93% to 99.8% reduction of viral RNA in samples collected from ivermectin-treated cells compared to the untreated control. These exciting results confirm that ivermectin is a potent inhibitor of the importin alpha/beta1 heterodimer, by which SARS-CoV-2 also seems to use in order to infect cells with virus.

A quick skim of Dr. Caly’s study, or an uninformed retelling of the study results, may suggest that ivermectin is an efficacious treatment to administer to COVID-19 patients. Scientific experiments were conducted by experts that show that ivermectin has potent antiviral effects, and the virus that causes COVID-19 was even tested directly.

So what’s the catch? Out of all of these studies, not a single one was performed in humans. When these studies talk about ivermectin’s antiviral properties, they are referencing observations and scientific data generated from cells grown in a lab. This is an excellent starting point for scientific discovery, but just because something works in cells doesn’t mean that it will work in animals, let alone the complex machine that is the human body.

In Vivo Failures

To the layreader, it can be difficult to discern if an experiment described in a scientific paper was conducted in vitro or in vivo. And how could the average layreader know such terminology when experimental methodology is hidden in the fine print of scientific papers? The ivermectin-COVID-19 debate is a great example of how poor scientific communication can lead to mass confusion and unnecessary conflict.

In vitro experiments are performed in cells. The literal translation of the Latin term is “in the glass”. Studies performed in vitro are performed in an artificial environment, like a test tube or cell culture plate. In vitro studies are performed outside of a living organism.

In contrast, in vivo experiments are performed inside a living organism. Preliminary studies performed on mice, toxicology studies performed on non-human primates, and clinical trials performed on human subjects all fall under the in vivo umbrella.

In order to be tested in humans, drugs must first prove to be efficacious in cells in vitro, and then efficacious and safe in animals that are less risky to dose than humans. Once a drug clears these hurdles and has sufficient data to suggest that it will be more helpful than harmful, only then is it tested in humans in clinical trials. Clinical trials themselves are thorough, multi-tiered investigations of a drug’s potency, efficacy, and safety that take years to see to completion.

In other words, the results of one study performed on cells grown in a tissue culture plate are not indicative of how humans will respond to such a treatment.

To muddy the waters even further, there have been several fraudulent and entirely fabricated “studies” on the human in vivo effects of ivermectin administered as an antiviral drug. To date, there are about 26 major in vivo clinical trials studying ivermectin as a COVID-19 therapeutic. About a third of these studies have been proven to be fraudulent or outright falsified. The remaining studies have yielded no data that suggests that ivermectin has any effect, let alone positive effect, on patients with COVID-19.

Perhaps one of the most well-circulated fraudulent studies is the Elgazzar paper⁶ out of Benha University in Egypt. The pre-print paper first came under scrutiny when Jack Lawrence, a masters student in the UK, read it and noticed several instances of plagiarism. When he reported his suspicions to researchers who assess fraud in scientific publications, even more fraudulent discoveries came to light. Patient data appeared to be fabricated, raw experimental data didn’t match up with conclusive remarks, and much of the experimental data was so mathematically unsound that it is likely it was generated falsely. There were even records of patient data stating that patients enrolled in the study actually died before the study’s start date. Among the most humorous pieces of misinformation was a patient leaving the hospital on June 31, 2020. Perhaps such a date exists in the equally fictitious world in which the study took place.

Despite such blatant transgressions on good science, the paper was viewed over 150,000 times and cited more than 30 times before it was withdrawn from the preprint platform.

The Elgazzar paper is far from the only “study” to report fraudulent in vivo ivermectin data. The authors of a study conducted in Iran⁷claim that half of all patients involved in the trial tested negative for COVID-19 upon beginning the study, completely negating the intended objective of studying the effects of ivermectin on COVID-19 at all. Other details in the paper’s methodology indicate that the poor randomization of results is likely due to fabrication of said results.

Desparate Times, Desparate Measures, and the Rise of Horsepaste

Once misinformation, like the “findings” reported in the aforementioned fraudulent studies, is shared by the scientific community, it’s even easier for the truth to be skewed by those with no scientific background, like many American politicians. This misinformation is more easily accessible to the public, and when the public is also desperate for a safe treatment to a deadly virus, a pandemic quickly becomes a pandemonium. To those looking for an alternative to the COVID-19 vaccines, an existing drug with seemingly reputable in vivo data becomes an attractive choice. This is what causes people to self-dose ivermectin for COVID-19.

When dosed properly (“properly” being a loose term, since ivermectin is nowhere near close to FDA approved for the treatment of COVID-19), administering ivermectin as a treatment for COVID-19 will likely not cause any harm, but it won’t treat or alleviate symptoms caused by COVID. This is based on what we know of ivermectin’s biochemical method of action as well as results from legitimate in vivo clinical trials of ivermectin as a COVID-19 therapeutic (such as the ongoing study at McMaster University⁸). However, this is under the generous assumption that those who are self-dosing ivermectin are adhering to appropriate human ivermectin doses. There is a large overlap between those desperate and misinformed enough to use ivermectin as a COVID-19 treatment and those who obtain ivermectin by means other than a pharmacy. This is more of a failing of the American health care and health insurance system than it is a reflection on those who choose to circumvent it.

Oftentimes veterinary ivermectin can be more easily obtained than human ivermectin, especially at places like livestock stores. This is where the real danger lies; livestock ivermectin is much more concentrated than human ivermectin. This makes it very easy to overdose on ivermectin and cause some pretty unpleasant and potentially lethal side effects. This is where ivermectin has gotten its notorious “horse paste” nickname. Ivermectin intended for horses is often packaged in a large syringe, with one full syringe containing enough drug product to dose a 1250 lb animal⁹. Each little line on the syringe indicates a dose for 250 lb of bodyweight. The difference in scale combined with the immense risk of inaccuracy of administering a horse drug to a human is the cause for a recent increase in calls to poison control. This year, the National Poison Data System reports a 163% increase¹⁰ in cases related to ivermectin alone. With more and more hospital beds being filled with unvaccinated COVID-19 patients, and less time that health-care workers have to spend on non-COVID-related cases, is OD-ing on an ineffective COVID treatment really something worth wasting one’s own time (and potentially life) on?

Impatience, the Most Deadly Side Effect of Good Science

Although in vivo clinical trials assessing ivermectin’s effects on COVID-19 still have a long way to go, the data generated so far concludes that ivermectin has no effect on treating the virus in humans. Despite tremendous in vitro success, ivermectin does not demonstrate the same antiviral efficacy inside the human body. However, these disappointing in vivo results don’t invalidate ivermectin’s antiviral in vitro triumphs; the experiments described in the Wagstaff and Caly papers discuss exciting discoveries that have led the scientific community closer to fully understanding the complicated world of viruses and how they work. Even more disappointing than ivermectin’s lackluster performance in the COVID clinic is how careless the global scientific community was to allow so many fraudulent in vivo studies to be publicly circulated. While political manipulation of scientific information is almost inevitable, the scientific community must take seriously its responsibility to publish high-quality and transparent peer-reviewed data.

The COVID-19 pandemic has skewed everyone’s sense of drug development timelines; multiple vaccines were developed and rolled out in less than one year. The secret sauce to developing a novel vaccine in no time at all is a tremendous amount of funding, huge public interest to boost clinical trial participation, and reductions in administrative red tape to speed up timelines. Not every scientific endeavor can, or should, have the same super-accelerated emergency timeline as the COVID-19 vaccines. Good science is methodical, deliberate, and oftentimes doesn’t yield the results you were hoping for. Good science isn’t always exciting or fun, but then again, neither is suffering damage done to your body and ego after self-administering medicine intended for an animal five times your size.

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