Ivermectin Use in Veterinary Medicine: What you need to know

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Portrait photograph of Dr. Joseph Smith

Written by Joseph Smith, DVM, MPS, PhD, , Assistant Professor of Farm Animal Medicine and Pharmacology, UTCVM Department of Large Animal Clinical Sciences.

On September 1, 2021, the American Medical Association, American Pharmacists Association, and American Society of Health-System Pharmacists released a statement on ending use of ivermectin to treat COVID-19.

Ivermectin is a member of the avermectin family of drugs that were originally developed in the 1970s. A researcher in Japan isolated a bacteria of the genus Streptomyces near a golf course in Honshu. The bacteria was noted to produce a compound that would clear roundworm infections in mice. In 2015, the researcher, Satoshi Ōmura, and his research partner, William C Campbell, received the 2015 Nobel Prize in Physiology or Medicine for the discovery of the avermectins.

Ivermectin functions by interfering with channels that are used to relay signals in nerve and muscle cells. The drug binds to these channels, and as a result, the channel is left in an “open” position, which allows for an increased inhibitory effect. This leads to paralysis and the eventual death of the parasite or insect. It is important to note that while parasites and insects are more sensitive to ivermectin, the drug can act on the same receptors in mammalian cells.

Ivermectin has many uses in veterinary medicine. As an anthelmintic (“Dewormer”) medication it can be used to treat multiple species of internal and external parasites. Internal parasite species that can be treated with ivermectin include gastrointestinal worms (primarily roundworms) in horses, cattle, pigs, sheep, and goats as well as lungworms in cattle and pigs. External parasites that can be treated with ivermectin in large animals include lice, mites, and grubs. In people, ivermectin is used for the treatment of river blindness (onchocerciasis) and lymphatic filariasis. It has additional uses for the treatment of lice and mite infestations in people.

There have been many recent reports of ivermectin as a possible treatment for COVID-19 in humans. It is important to keep in mind that these are preliminary studies that have not yet led to approved treatments by the US Food and Drug Administration (FDA). Currently, robust and controlled studies on the effectiveness and safety of ivermectin for COVID infections are lacking. The FDA warns, “Using any treatment for COVID-19 that’s not approved or authorized by the FDA, unless part of a clinical trial, can cause serious harm.” Ivermectin can cause toxicity in people, with adverse effects as severe as ataxia, coma, nervous system depression, and death. Using large animal formulations of ivermectin in species where it is not approved has led to overdose situations. For example: in the veterinary literature there are reports of ivermectin overdoses from the administration of the equine product to dogs, cats, ponies, and goats. At this time the FDA does not recommend the use of ivermectin to treat or prevent COVID-19. People should discuss disease treatment or prevention with their health care provider.