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A New Mouse and Rat Poison Poses Deadly Threat to Dogs

The EPA has put restrictions on certain types of rodenticide, which dogs and other animals frequently consume; some have no antidotes.

 |  Sep 2nd 2014  |   1 Contribution


Any poison that can kill rodents also can kill dogs. And unfortunately any bait that is attractive to rodents will also be attractive to dogs. So-called rodenticide toxicity is therefore among the most common forms of poisoning in dogs.

Mouse and rat baits come in three varieties. One relatively uncommon variety contains products similar to vitamin D. These products can cause kidney failure in dogs. Other products I'll write more about later in this post contain an active ingredient called bromethalin that is a nerve poison. Finally, some products contain toxins that make it impossible for blood to clot.

The last group, known as anticoagulant rodenticides, historically have been the most widely used in the United States. They cause death by hemorrhage, and they are toxic to all mammals. There are different types, or generations, of rodenticides. The later generations are phenomenally deadly to dogs.

Dogs that have consumed anticoagulant rodenticides show no symptoms for several days. However, once the symptoms start, the situation becomes an urgent veterinary emergency. Dogs may bleed into their lungs or into their chest. They may cough up blood or become short of breath. Bruising of the skin or gums may occur. Blood may be noted in the mouth, urine, or stool. Weakness, poor appetite, or lethargy may be seen. Death occurs as a result of blood loss or from compromise of vital structures secondary to internal hemorrhage.

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Photo of Dr. Eric Barchas by Liz Acosta

There is plenty of bad news about anticoagulant rodenticides, and dogs that show symptoms after consuming them are nearly certain to die without treatment. However, there is one bit of good news. Anticoagulant rodenticide poisoning is treatable.

There is an antidote for the poisons: vitamin K1. In dogs that have consumed the poisons within the previous three days, administration of vitamin K1 alone is generally sufficient to prevent symptoms and complications. In dogs with symptoms, a transfusion of a blood product called plasma, combined with vitamin K1 administration, usually reverses the toxicity and saves the dog's life.

Identifying the toxicity is usually simple, even in cases when the owners don't know the poison has been consumed. Simple blood tests can identify the problem in a matter of minutes in most cases.

I've never been a fan of anticoagulant rodenticides, but at least they are not difficult to diagnose and treat.

It turns out that the U.S. Environmental Protection Agency also is not a fan of anticoagulant rodenticides. The agency issued severe restrictions on the products in 2011. And in July the Journal of the American Veterinary Medical Association reported that the last company to fight the regulations (the manufacturer of d-Con) has agreed to comply.

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Kills mice? Yes. Kills dogs? Yes! Photo by Genista

The EPA instituted the restrictions over concerns about exposure of children, pets, and wildlife. The agency reports that exposure of children (which I imagine is the agency's greatest concern) has decreased by 50 percent since the regulations went into effect. The agency also released some rather alarming statistics about wildlife exposure to support the restrictions. From the JAVMA article:

Agency documents filed in mid-2008 indicate a study in New York found residues from second-generation anticoagulants in 48 percent of diurnal raptors and owls analyzed. In California, residues were found in more than 70 percent of bobcats, mountain lions, and San Joaquin kit foxes analyzed.

The JAVMA article goes on to discuss the epidemiology of rodenticide toxicity in pets. Predictably, since the institution of the regulations, pet exposure to anticoagulant rodenticides has decreased. However, total rodenticide exposures have remained stable. That means exposure to one of the other poisons has gone up.

That other poison is bromethalin.

Bromethalin is a neurotoxin. It causes the brain to swell. Symptoms of bromethalin ingestion may be delayed by several days after exposure. The symptoms may include tremors, behavior changes, weakness or staggering (especially in the hind end), and hyper-responsiveness to stimulation. Severely intoxicated individuals may suffer seizures, coma, and death.

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Labrador Retriever at the vet by Shutterstock.

The symptoms of bromethalin ingestion are very nonspecific -- just about any neurological condition, including other toxins, head trauma, brain tumors, and meningitis, can look identical. There is no point-of-care diagnostic test for bromethalin. There is no antidote.

That is the bad news. Fortunately, there also is good news. Bromethalin generally is much less toxic than the anticoagulant rodenticides. When dogs break into anticoagulant rat baits, they nearly always consume a fatal dose. When they eat products that contain bromethalin, they most often do not.

The treatment for bromethalin toxicity is symptomatic care with IV fluids, antiseizure medications as needed, and nursing support. The article in JAVMA reports that "dogs that receive early, appropriate treatment for bromethalin poisoning tend to recover well." That statement is compatible with my personal experience; I have treated a large number of dogs for bromethalin ingestion, and I have yet to lose one.

Nonetheless, remember that bromethalin is potentially deadly to dogs. And remember that there are ethical issues with rodenticide use as well. Mice and rats may be pests, but they are mammals with a capacity for suffering that is similar to that of dogs. Death by rodenticide is not pleasant.

Whether you have a dog or not, I do not recommend use of rodenticides. Traps are more humane, and pet-friendly traps pose less risk to your -- or your neighbor's -- beloved furry friend.

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