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Of Mice and Mayhem: A Rodenticide Story

By Kim Everson, DVM

An urgent call comes in late one afternoon.

“My dog just ate rat poison! What do I do?”

In my experience as veterinarian and pet owner, rodenticide ingestion is a pretty common problem. My own dogs once discovered an unknown stash of warfarin pellets, ate it and then, before I could clean it up, ate the pile I made them vomit up. Geniuses. All of us.

Veterinarians field this type of call regularly. If the case involves a typical poison and is caught early, prognosis is very good with aggressive treatment. This time, however, the owner’s next utterance stopped me cold.

“It’s bromethalin.”

Not a warfarin-type rodenticide, I thought to myself. Oh boy. And the packaging instructed not to induce vomiting, often our first line of defense in cases like this.

“I want you to hang up and call Animal Poison Control at 1-888-426-4435 and explain the situation,” I instructed. “They will give you a case number for Rosco so we can handle this exactly right on our end. In the mean time, I will look into this particular rodenticide as well and call you back shortly.”

Bruising on gums caused by
anti-coagulant rodenticide toxicity

As I feared, bromethalin is handled nothing like warfarin. Warfarin is an anti-coagulant that was developed for use as a rat poison by University of Wisconsin chemists in the 1940s. (It is now also widely used as an anti-clotting medication in people!) Warfarin interferes with the liver’s ability to make clotting factors. Without vitamin K supplementation, affected animals bleed to death from internal and/or external bleeding. It may take one to five days before clotting problems start, but if a pet is caught in the act of eating a warfarin rodenticide, treatment begins immediately and most pets (like mine) recover uneventfully.

Mankind keeps trying to invent a better mousetrap, or in this case, rodenticide. There are multiple chemical offspring of warfarin which are more potent and require longer vitamin K supplementation, but bromethalin is in a class all its own. Invented when rats became resistant to warfarin, bromethalin causes swelling within the brain and spinal cord leading to depression, stumbling, paralysis, seizures, coma and death. Unlike warfarin’s vitamin K, there is no specific antidote for bromethalin toxicity. Prognosis is pretty grim, especially if pets are already showing symptoms when diagnosed.

Dog hunts rodents in his backyard

Luckily it was determined that Rosco did not ingest enough of the bromethalin brick for it to cause toxicity. The owners were told to watch Rosco closely and bring him in to the clinic for supportive care if he showed any neurological symptoms.  I’m glad to report that Rosco has had no signs of toxicity since the incident! Unfortunately, the owners now face the daunting task of locating untold numbers of bromethalin bricks buried in their backyard. In their war against the rodents invading their basement, this family has unwittingly become trapped inside a veritable mine field of deadly rodenticide bricks.

Dead hawk resulting from rodenticide toxicity

Rodenticide toxicity is not just a problem for pets. Just as mercury “bioaccumulates” in marine food chains making it dangerous for people to eat too much of certain fish from certain waters, rodenticides affect large birds of prey such as red tail hawks. These predators eat affected rodents (easy pickin’ because they’re sick) and over time the toxins make the birds very sick. Rodenticide poisoning and death among unintended wildlife victims is a disastrous consequence of our efforts to control rodents using increasingly potent chemicals. Just as strychnine use in Wisconsin requires special permitting because of its potential to harm non-target animals, there are many who would like to see tighter controls on modern heavy-hitting rodenticides as well. If you must use a chemical means to control rodents, please follow the package directions carefully to limit the poison’s impact on non-target creatures.

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