Ask the Vets

I put some rat poison around our shed outside and I think our dog may have gotten into it. I have heard it can poison a dog but my dog looks normal.  What should I watch for?

It’s that time of year again when rodents are trying to make their way into buildings to find shelter for the winter ahead.  Rat and mouse poisons (rodenticides) are readily available and frequently used to control rodent populations, which is why accidental exposure in pets is common.  In January 2013, Health Canada imposed restrictions on the use of several commercial class rodenticide products with the intent to reduce and prevent the accidental exposure of children and non-target animals.

There are many different types of rodenticides available.  Three of the more common types include anticoagulants, metal phosphides and cholecalciferols (Vitamin D) rodenticides.    

The most common rat and mouse poisons are the anticoagulant rodenticides (e.g. brodifacoum, diphacinone, warfarin, bromadiolone, etc.).  They act by blocking an enzyme that allows the recycling of Vitamin K by the liver.  The body needs Vitamin K to allow the blood clotting process to occur normally.  When the body runs out of Vitamin K, excessive bleeding begins.   In cases of poisoning you would expect symptoms to be nearly immediate but it actually takes several days to deplete the body’s store of Vitamin K.  After that, even the smallest injuries or bumps can lead to life-threatening bleeds.  Most of the time external bleeding is not obvious and you only notice the pet is weak and/or cold. If you look at the gums, they are sometimes pale.  Blood in the urine or stool, nose bleeds or bleeding from more than one body location are a good hint that there is a problem with blood coagulation and appropriate testing and treatment should be started.  Never wait until symptoms occur; the chances of surviving the poisoning are greatly improved with intervention before bleeding begins.  If widespread bleeding has already started, the prognosis is much more guarded to poor.  Risk of secondary poisoning from eating the dead rodents is another concern that must be taken into account when using baits around your property.

Metal phosphide rodenticides (usually zinc phosphide) are fast acting and kill the rodent within 1-3 days after ingestion.  Once ingested, the stomach acid reacts to the phosphides and produces toxic phosphine gas that rapidly leads to cell death especially in the heart, brain, kidney and liver.  The phosphide rodenticides can be very dangerous to manage because when the pet vomits up the ingested material, phosphine gas is released, posing danger to the people handling the animal and vomited material.  Inducing vomiting for this poison should never be attempted at home.

Cholecalciferols or Vitamin D rodenticides (e.g. bromethalin) lead to a life-threatening rise in blood calcium levels that causes organ failure.

The product name and estimated amount of bait ingested should be reported to your veterinarian as soon as any exposure has occurred and treatment should be sought immediately.  Knowing what kind of rodenticide has been eaten, will guide in the treatment decisions.   If the pet has recently ingested the poison (i.e. within hours), your veterinarian can administer medication to induce vomiting.   Cathartics and adsorbents can be used to prevent or limit the poison from entering the patient’s system.

In the case of anticoagulant rodenticides, a blood test can be done to measure your dog’s clotting ability to see if an exposure has occurred.  Since there is an antidote for this type of exposure, supplementing the patient with enough Vitamin K will ensure clotting will be able to continue as normal and prevent bleeding.  Vitamin K may need to be continued for up to 4-6 weeks until the chemical is no longer interfering with the clotting pathway.   The blood test may also be repeated at the end of treatment to ensure your pet is safe to discontinue the supplement.

If poisons must be used, a first generation anti-coagulant rodenticide is the best choice as it often takes more of the bait to cause a poisoning, an antidote is available should an exposure occur and these poisons tend not to linger in the body as long.  Keep your pet safe by supervising outdoor time, keep them leashed in known baited areas, bait areas that are inaccessible to pets and ensure any baits that are needed are in a pet-safe containment device to prevent access to the bait block or pellets.   Visit the Health Canada website at http://www.hc-sc.gc.ca/cps-spc/pubs/pest/_fact-fiche/restriction-rodenticides/index-eng.php, to read up on the requirements for safe use and suggestions for baiting stations.  Please contact your veterinarian to follow-up on your dog as soon as possible.  We wish you all the best and hope your dog makes a full recovery.

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