Rodenticide Refresher for Veterinary Professionals

By Ahna Brutlag, DVM, MS, DABT, DABVT
Director, Veterinary Services & Senior Veterinary Toxicologist at Pet Poison Helpline
June 20, 2019

Pet exposure to rodenticides (mouse and rat poisons) always ranks amongst the top 5 cases managed by Pet Poison Helpline and right now is no exception. Refresh your memory and learn about what’s new with rodenticides in 2019.

Rodenticides are easy for people to obtain and commonly used in residential or agricultural settings such as homes, garages, lake cottages or summer homes, barns, farms, and even parks or wildlife areas. They’re available in a wide variety of colors (e.g. green, blue, tan, red, beige) and formulations (e.g., bait blocks, soft baits, pellets, grain-based baits, liquids, etc.). Too add to the confusion, different rodenticides may look alike and have similar names, but contain different active ingredients. There is no market standardization for rodenticide color, formulation, and corresponding active ingredient.  Therefore, if a pet ingests a rodenticide, accurate identification of the active ingredient is crucial as this will determine the risk of poisoning and the need for treatment.  If the active ingredient is not clearly visible on the packaging, another important identifier is the EPA registration number (EPA Reg. No.) – this number will allow Pet Poison Helpline veterinarians to correctly identify the active ingredient and corresponding percentage.

Below are the three most common rodenticide active ingredients/ingredient classes, along with their mechanism of action, clinical signs of poisoning, and treatment options.

ANTICOAGULANTS: Anticoagulant rodenticide exposures in pets have taken a nosedive. Ten years ago, anticoagulants represented nearly 80% of PPH’s rodenticide cases. Now, they represent just 35%. Why the change?  As of 2011, EPA prohibited second generation anticoagulant rodenticides from residential use unless applied by a professional. As a result, manufacturers shifted to other active ingredients.

Anticoagulant rodenticides are divided into first- and second-generation products. First-generation baits are typically shorter-acting (e.g., warfarin) with second-generations baits being longer-acting (e.g. brodifacoum, bromadiolone). For the past several decades, second-generation baits have been the most commonly used rodenticide in residential settings. Not anymore. For more on this topic, click here.

  • Mechanism of action:of the enzyme Vitamin K1epoxide reductase, which ultimately decreases the concentration of active clotting factors 2, 7, 9, and 10. This results in uncontrolled bleeding. When healthy dogs or cats ingest anticoagulant rodenticides, 3-5 days pass before signs of poisoning are visible; however, if the pet has been chronically exposed to the product, the onset of clinical signs may be sooner.
  • Common signs of poisoning:Initially, blood loss is typically internal (intracavital) and signs include lethargy, exercise intolerance, coughing, difficulty breathing (due to bleeding into the lungs), weakness, and pale gums. Less common signs include vomiting, diarrhea (with or without blood), nosebleed, bruising, bloody urine, swollen joints/lameness, inappetence, and bleeding from the gums.
  • Antidote and treatment:Vitamin K1 (phytonadione) is the antidote. Menadione (Vitamin K3), over-the-counter multi-vitamins containing K1, or food with a high vitamin K are not sufficient substitutes. If poisoning occurs, most pets need to be treated with oral Vitamin K1 for 5-10 days (first generation) or 21-30 days (second generation). Two days after the last dose of Vitamin K1 is administered, a prothrombin time (PT) should be checked to make sure the clotting is normal.
  • Threat:Certain species, such as cats, are more resistant to the effects of these baits and rarely suffer poisoning. Dogs, on the other hand, can be quite sensitive and often require veterinary intervention. In addition, the dose needed to cause poisoning from varies greatly between active ingredients making accurate product identification important to a successful treatment plan. With some baits (e.g., brodifacoum), it takes only a very small amount to cause poisoning in canines, while others have a wider margin of safety (e.g., bromadiolone) and larger amount is needed to cause poisoning. The age and health of the pet are other risk factors . Animals with underlying liver or gastrointestinal disease, as well as the very young or very old, are more at risk.

CHOLECALCIFEROL (VITAMIN D3): For dogs and cats, this is one of the more dangerous rodenticides on the market and is gaining in popularity primarily due to EPA restrictions on second-generation anticoagulant rodenticides. It is now sold under the d-CON brand in a soft bait formulation. See our 2018 webinar on this popular topic.

  • Mechanism of action: Causes hypercalcemia and hyperphosphatemia, resulting in acute kidney failure and other tissue damage secondary to dystrophic mineralization.
  • Common signs of poisoning:PU/PD, weakness, lethargy, decreased appetite, and halitosis (“uremic” breath). Acute kidney failure develops 2-3 days after ingestion. Often by this point, significant and permanent damage has already occurred to the body.
  • Antidote and treatment:This poisoning can be one of the most challenging to treat since hospitalization, frequent laboratory monitoring, and expensive therapy is often required for a positive outcome. Poisoning generally responds well to 2-3 days of aggressive IV fluids and specific drugs, especially bisphosphonates which help decrease calcium concentration in the body. Frequent monitoring of blood work (calcium, phosphorus, and renal values) is often needed for a period of 2-6 weeks after ingestion. Intralipid (ILE) therapy is not currently recommended.
  • Threat:Cholecalciferol has a very narrow margin of safety, and even small ingestions of this bait can result in severe clinical signs or death. Toxic ingestions must be treated quickly and appropriately to prevent kidney failure.

BROMETHALIN: This neurotoxic rodenticide causes cerebral edema. Because the ingredient name looks like some anticoagulant rodenticides (e.g., brodifacoum, bromadiolone, etc.), it may be easily mistaken for a one.

  • Mechanism of action:Bromethalin is thought to work by uncoupling oxidative phosphorylation in the brain and liver mitochondria and can result in cerebral edema.
  • Common signs of poisoning:Incoordination (ataxia), tremors, seizures, paralysis, and eventually death. The larger the ingestion, the more severe and rapidly occurring the clinical signs may be. Signs can develop within 2 hours following ingestions above the LD50, but may be delayed as long as 3-4 days if the ingested toxic dose was less than the LD50. Thus, medical monitoring for at least 24 hours after ingestion of toxic amounts is often necessary.
  • Antidote and treatment:In-hospital care for several days may be necessary because this poison has a long-half-life and long-lasting effects. Treatment may include multiple doses of activated charcoal, IV fluids, and specific drugs to decrease brain swelling.
  • Threat:Cats are more sensitive to bromethalin than dogs are. As this type of rodenticide has a narrow margin of safety, prompt therapy is often needed in all species.

What to do in case of pet exposure: Whenever possible, determine the rodenticide’s active ingredient and amount ingested. Exposures may be sub-toxic and not require treatment. Early consultation with the veterinary toxicology experts at Pet Poison Helpline will provide veterinarians with an appropriate and tailored plan for the patient.  In the case of toxic exposures, appropriate at-home induction of emesis (dogs only) may be helpful prior to an in-hospital examination. In cases involving delayed ingestion or where at-home decontamination would not be advised, rapid transport to the hospital may be necessary. From here, treatment and diagnostic recommendations vary based on the dose ingested and active ingredient.