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Sonoma County Gazette
The Family Pet by Dr. Michael Trapani

DANGERS of RAT Poison.
It kills more than rats!

Feb 2, 2018
by Dr. Michael Trapani


“You want proof evolution is for real, don’t waste your time with fossils; just check out the New York City rat. They started out as immigrants, stowaways in some ship’s cargo hold. Only the survivors got to breed, and they’ve been improving with every new litter; smarter, faster, stronger, getting ready to rule. Manhattan wouldn’t be the first island they took over.” – Andrew Vachss


White Domestic PET RatRats as PETS: Taken as individuals, rats are pretty decent creatures. Human-raised, humane-bred rats, that is. It’s hard to find a cleaner, smarter, more outgoing pet for a young child than a common domestic rat. They enjoy being handled, are happy to hang out in a coat pocket for hours, and gleefully share a kid’s peanut butter sandwich at lunch time. Ya gotta love ‘em.

Rats as PESTS: Not so much though, when their wild relatives are scraping around inside the wall of your bedroom, breeding in your pantry, or chewing through the wiring harness of your new car. A professional exterminator may charge $400 to $500 just for the initial home visit to identify the type of rat, its means of entry, and the extent of damage they have created. Automobile repair costs have been reported at several thousands of dollars to repair rodent damage. It’s no surprise that people commonly use readily available, over-the-counter rodent poisons to eliminate rat populations. These seemingly safe products are cheap and available in almost all hardware stores, and even supermarkets.

Brown Wild PEST RatWhat could possibly go wrong?

There are two general groups of rodent poisons: Anticoagulants and “Other. ”Anticoagulants are related to warfarin, which competes with vitamin K for access to liver cell enzymes used to synthesize necessary blood coagulation proteins. These poisons are available in first and second generation forms, with later generation products being generally more powerful and persisting in the rodent’s body for longer periods of time. Examples of these poisons include warfarin, difenacoum, brodifacoum, bromadiolone, diphacinone, and pindone, among others. I won’t mention any names, but you already know the products. Many of these brands are household names.

It should be noted that anticoagulants are slow poisons that must be eaten during several meals before a lethal dose is taken in. It takes a while, perhaps one to two weeks (rarely less), for a rat to accumulate a lethal dose of anti-coagulant poison. Only then does the poisoned rat sicken due to internal bleeding. These effects are gradual, developing over several days. In the final phase of the intoxication, the exhausted rodent collapses from shock or anemia and dies quietly. Whether the use of these rodenticides can be considered humane is a matter of debate.

The “Other” category of rodenticides is quite broad and includes such things as white phosphorous (a precursor to nerve gas), strychnine (a neurotoxin causing seizures), chloralose (a narcotic pro-drug), thallium (a cellular toxin), and hydrogen cyanide gas (bonded to a carrier). Perhaps the worst of these is bromethalin (now that’s saying something), which uncouples the energy production mechanisms in mitochondria, causing increased intracranial pressure which permanently damages nerve cells, resulting in paralysis, convulsions, and death.

Other animals, such as dogs, cats, owls, hawks, eagles and also mammals such as foxes, bobcats, raccoons, mountain lions, and coyotes, readily feed on rodents, particularly those who have been weakened and slowed due to poisoning.

Dying rodents contain enough poison to kill the predator that eats them, resulting in secondary, or even tertiary poisoning when scavengers feed on predators killed after eating poisoned rodents.

Children are also at risk.The U.S. Environmental Protection Agency has known for decades that kids have too-easy access to rat poisons. Every year more than 10,000 kids are exposed to them, and virtually all of the calls to U.S. poison control centers concern children under six.

Anti-coagulant toxicity can be managed with massive and extended doses of vitamin K. A typical patient is treated by induction of vomiting to completely empty the GI tract. Obviously, this helps most when vomiting is induced immediately after the poison is ingested. Then, activated charcoal is administered at a dosage and frequency appropriate for the poison in question and the level of exposure. Vitamin K is given by injection and orally for a period long enough to allow the patient to eliminate the anticoagulant. This may take weeks, and vitamin K is not cheap. Neither are the blood coagulation monitoring tests required to determine when the patient is out of the woods.

“Other” rodenticides must be treated according to the type of poison ingested. This is why it is always critical to obtain the package label whenever rodenticide poisoning is suspected. Knowledge of the exact poison consumed, along with the strength of the product and size of the bait blocks is crucial to establishing a successful treatment. Bromethalin is a particular problem.

There is no antidote and therapies directed at the effects of the poison have only limited success.

Here’s the thing: When we put these poisons out into the environment, they don’t stay where we put them. Wherever they wind up, they are likely to persist for a long, long time. Non-target animals, like that gorgeous owl or eagle we’re all so thrilled to see, readily become unintended victims of our efforts to control problem rodent populations. In our quest to control rats, poisons should be our last choice, not our first.

What to do? Environmental management is the best place to start.Un-clutter your yard to eliminate rodent’s cover and breeding areas. Inspect the exterior of your home and seal holes to prevent rodents from getting inside. Non-toxic rat baits, such as ground corn cob, can be placed near rat burrows and used to kill the rodents. Mothballs can be used to repel rats. Keep trash cans thoroughly sealed and avoid placing edibles in compost to prevent attracting rats to your property. There are a dozen varieties of traps, from traditional snap traps to electrocution traps to catch and release traps that can be obtained. Get a cat (or three) to repel rodents with their scent and reduce rodent numbers through hunting.

But whatever you do, DON’T go broadcasting poison where wild animals, or your pets (or your neighbor’s pets) will become unintended victims!The Family Pet by Dr. Michael Trapani


Feb 3, 2018
Thank you for this excellent article, Dr. Trapani. We ( have been working to educate the public about these poisons in the ecosystem and the serious toll they are taking on wildlife for several years after finding Cooper's hawks and barn owls bleeding out on the streets. It is great to see this article coming from a vet; wish more veterinarians would do the same!
- Lisa Owens Viani
Feb 3, 2018
Rat poison is indeed a threat to pets and wildlife. Two caveats on alternatives: 1. Powdered corn cob appears to be inhumane, since it starves rodents, leading to a slow death. 2. Mothballs are poisonous to people and pets.
- David Shellenberger

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