With the thawing of February and March’s snow, many rodents and varmints have come out of their winter slumber. This makes this season a favorite time of year for our pets that love to hunt! Unfortunately, this is also the time of the year that vets treat the highest frequency of cases of rodenticide toxicity.

There are many types of commercial and over-the-counter rodenticides available. The traditional second generation rodenticide d-CON products have not been manufactured since 2014 nor sold since 2015 due to pressure from activist groups and the Environmental Protection Agency. 

These type of products kill rats, mice, varmints after one feeding and have the potential to kill animals that ingest the affected rodents. It is not recommended to use these products or keep them around your house, garage, or barn. d-CON products should only be used by licensed professionals and must be kept in secure bait stations. 

Currently, the most popular types of rodenticides that are being sold are bromethalin-based rodenticides and anticoagulant rodenticides (brodifacoum, bromadiolone, warfarin, etc). 

Bromethalin rodenticides were created in 1985 and thought to be a better alternative than second generation rodenticides, especially as the d-CON generation were phased out of mainstream distribution. 

Bromethalin rodenticides use a smaller amount of poison and do not pose a threat of death for the predator that eats affected rodents or moles. These products can be used directly on the ground or within pet-safe containers. These rodenticides act by uncoupling oxidative phosphorylation in the brain. When this occurs, the brain can no longer use oxygen to make energy. Without aerobic metabolism the brain begins to swell leading to fatal cerebral edema. When high doses of bromethalin are ingested the convulsant form of poisoning ensues within hours and death is essentially inevitable. The convulsant form begins with hyper-excitability, hyperthermia, seizures, and then proceeds to death. 

When lower doses are ingested the paralytic form of poisoning ensues. This can take up to four days and begins within inappetence, lethargy, ataxia in the rear legs, and progresses to paralysis and ultimately death. This form can be treated if caught early and requires aggressive in hospital management that is tailored to the patients symptoms. 

First generation anticoagulant rodenticides are preferred over bromethalin-based rodenticides because if they do accidentally get ingested there is at least an antidote — Vitamin K. Anticoagulant rodenticides act by altering the coagulation cascade. 

The coagulation cascade is very complicated and one of the most amazing things the body does. A key player in this cascade is Vitamin K. When there is leakage from blood vessels the coagulation cascade gets initiated. 

Platelets clump together at the opening of the vessel, clotting factors are activated, and fibrin comes in to bind the platelets together and form a plug. The clotting factors are produced by the liver and remain inactive in circulation until Vitamin K activates them. Once they are activated, Vitamin K is inactivated by a series of enzymatic reactions and is recycled by the body to be used again. 

Anticoagulant rodenticides act by turning off Vitamin K recycling so that once the Vitamin K gets used initially to stop bleeding, it is depleted from the system. It takes multiple days to fully deplete the system of Vitamin K which is why clinical signs are not usually apparent until a few days after ingestion. 

While Vitamin K is the antidote to accidental anticoagulant rodenticide ingestion it is recommended to seek veterinary attention immediately instead of purchasing this over the counter. Depending on the amount and type of rodenticide ingested and the size of the dog treatment can vary significantly. Blood transfusions may be needed depending on severity. 

Once the body begins to bleed out of the major vessels treatment is often not successful. Treatment can range from 2-8 weeks. Blood tests evaluating PTT (partial thromboplastin time) and PT (prothrombin time) are obtained 48 hours after the last dose of Vitamin K has been administered to ensure that the treatment course does not need to be extended. 

If your pet is acting abnormal, may have ingested rodenticide, or was observed ingesting rodenticide please contact your veterinarian and seek treatment immediately! These are not benign things to ingest and quicker treatment typically has much more successful outcomes.

Danielle Carey, DVM, is an associate veterinarian who practices mixed-animal veterinary medicine at the Animal Clinic of Walla Walla. Contact her at 509-525-6111.

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