What is ivermectin? How a livestock dewormer became a rumored COVID-19 aid with bad side effects

‘There have been lots of cases of liver problems and liver failure, severe GI upset and even things like seizure and coma,’ says UCLA Health’s Dr. Dan Uslan.

You know things are bad when the U.S. Food & Drug Administration posts a drug warning on social media that reads, “You are not a horse. You are not a cow.”

That’s what the agency did in August to discourage consumption of ivermectin, an anti-parasitic medication most often used as a livestock dewormer that’s become a sought-after yet unproven drug to treat or prevent COVID-19.

“People are devastated by COVID-19, so they want a quick fix or a magic-bullet solution,” says Dan Uslan, MD, clinical chief of infectious diseases for UCLA Health. “But it is painstaking scientific testing, not magical thinking, that reveals what works well. Unfortunately, with ivermectin, the studies have really not found that it is an effective medication, either for treatment or for prevention.”

The FDA and the National Institutes of Health caution against using ivermectin for COVID-19. But that hasn’t stopped people from seeking prescriptions, which have skyrocketed to 88,000 a week nationally from a pre-pandemic baseline of 3,600 a week, according to the Centers for Disease Control and Prevention.

Ivermectin is FDA approved for use in humans to treat river blindness, a parasitic condition caused by blackfly bites. “Ivermectin in doses we use to treat parasitic infections is generally a very safe drug,” Dr. Uslan says.

However, because the medication is so often used in animals it’s available without prescription in many farm and feed stores, and people have been clearing the shelves. Calls to poison-control centers have spiked as individuals have self-medicated with ivermectin preparations intended for a 1,500-pound cow or horse. There have also been reports of people ingesting topical formulations.

“Ivermectin is potentially a very toxic drug,” Dr. Uslan says. “There have been lots of cases of liver problems and liver failure, severe GI upset and even things like seizure and coma.”

In March and again in August, the FDA issued a warning against using ivermectin for COVID-19.

"Ivermectin is potentially a very toxic drug," says Dr. Dan Uslan.

How ivermectin became a rumored COVID cure-all

In laboratory studies, ivermectin has been shown to kill the virus that causes COVID-19, Dr. Uslan says. In theory, the drug works to interfere with how the virus gets into cells.

“There is some scientific rationale for why it would be a good medication for treating viral infections like COVID-19,” he says.

Studies of its use in people with COVID-19, however, have not yielded any meaningful results, Dr. Uslan says. Ongoing scientific studies, including one at the University of Oxford, are exploring whether ivermectin is effective as a treatment for COVID-19.

Desperate for a remedy

What causes the fervor around unproven remedies for COVID — such as ivermectin now and hydroxychloroquine earlier — is a profound desire for a way to treat or cure this devastating virus, Dr. Uslan says.

“People are desperate for a medication that is highly effective against COVID-19,” he says. "Especially an oral medication that could be used for not only treatment of people, but even prevention of infection.”

The only outpatient COVID-19 treatment currently available is monoclonal antibody therapy, used under emergency use authorization with high-risk patients. For hospitalized patients, treatment may include steroids or the antiviral drug remdesivir.

Scientists are looking to develop an oral antiviral medication for COVID-19, much like Tamiflu targets influenza.

“That’s an area of active study,” Dr. Uslan says. “But ivermectin is not that thing.”

Meanwhile, he says, the best, scientifically proven ways to prevent COVID-19 remain vaccination against the virus and regular use of face masks.


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