Rodenticide Toxicity

There are four main groups of rodenticides, each with its own mechanism of action and clinical presentation in non-target species.

1. Anticoagulant rodenticides are probably the most well-known group of rodenticides and are still readily available today. From a pet owner standpoint, this is the safest group of rodenticides for our pets to accidentally consume.

   1. Dogs are more sensitive to these compounds than cats. These compounds interrupt the activation of vitamin K which is necessary for the body to manufacture clotting factors.

   2. Clinical signs are the result of hemorrhage, but can be quite variable depending upon the site of hemorrhage. A large percentage of animals will hemorrhage into the lungs, thus, bloody nasal discharge and coughing blood are common with concurrent lethargy, exercise intolerance, difficulty breathing and pale mucous membranes. Animals can bleed from virtually any site so clinical signs may include bloody feces (sometimes black and tarry feces which is a sign of digested blood), blood in the urine, bruising of the skin, bloating of the abdomen.

   3. Clinical signs are typically delayed 3-5 days after an animal consumes a large enough dose. Your veterinarian will likely run blood tests to confirm the diagnosis and determine if more advanced life saving measures are needed like a blood transfusion. Vitamin K1 is the antidote and is given for 3-6 weeks depending on the type of anticoagulant used.

   
   

   

2. Bromethalin is another common compound found in OTC rodenticides, unlike the anticoagulants, cats are more sensitive to bromethalin than dogs.

   1. Bromethalin causes brain swelling due to loss of energy in the neurons.

   2. Bromethlin can cause different clinical signs depending on the magnitude of the dose consumed; these signs include:

      - severe tremors

      - hyperexcitability

      - seizures.

   Lower dose exposures are more common clinically and result in a delayed onset of milder clinical signs. Signs may be delayed for several days and include hind-limb ataxia and paresis (similar to tick paralysis or botulism) which can progress to seizures if untreated.

   
   

   There is no antidote for bromethalin, so early decontamination is extremely important. If an animal ingests a toxic dose of bromethalin, promptly inducing vomiting can be lifesaving. After vomiting has occurred, multiple doses of medical-grade activated charcoal are administered over 24-36 hours and intravenous (IV) fluids are delivered to maintain hydration.

   
   

   Close electrolyte monitoring is important to watch for elevated sodium levels. If clinical signs develop, mannitol is started to decrease cerebral edema. Clinical signs are then treated with anticonvulsants, muscle relaxants, antiemetics, and GI prokinetics, as needed. The prognosis is poor to grave.
   

3. Cholecalciferol rodenticides are also available, and the clinical presentation is identical to vitamin D toxicosis from ingestion of vitamin D supplements. Clinical signs are relatively nonspecific and are typically delayed 36-48 hours post-exposure.

   1. Anorexia, weakness and depression may be identified early in the progression of signs followed by vomiting, polyuria/polydipsia and dehydration as renal function deteriorates.

   2. Acute renal failure develops within 2-3 days of exposure.

   3. Hypercalcemia and hyperphosphatemia are readily identified and are commonly elevated enough to result in soft-tissue mineralization.

      
      

      Treatment of clinical cases is expensive and drawn-out. Various combinations of calcitonin, bisphosphonates, corticosteroids and loop diuretics have been used historically. Prognosis is typically guarded to poor.

      
      

The last group of rodenticides are the phosphides.

4. Zinc and aluminum phosphide are available for purchase, zinc phosphide is the most common. Zinc phosphide is typically used underground to target moles and gophers. The zinc portion is a strong emetic which can be protective in non-target species. In an acidic environment like the stomach, the zinc portion is cleaved and results in the production of phosphine gas which is a dangerous systemic poison.

   1. Clinical signs occur rapidly, often within an hour of exposure.

   2. Clinical signs include severe gastrointestinal signs and hemorrhage, with rapid progression to systemic signs including pale or blue mucus membranes, shock, convulsions, and death.

   3. Phosphine gas is a hazard for veterinary staff, and affected animals should be handled in a well-ventilated space or outdoors. Phosphine gas has a fishy or garlic smell that is detectable by humans around 2ppm, this is double the EPA limit of 1 ppm for brief exposures.

   4. Therapy is typically supportive in nature. Despite the severity of clinical signs many dogs can make a full recovery, especially those that survive the first 24 hours.

      
      

      There is no antidote for the phosphides, antacid therapy and decontamination can be effective, but care should be taken to protect veterinary staff.

      
      

***Especially in Canada, there is another more rodenticide that is very common, corn cellulose powder.

5. Corn cellulose–based rodenticides are made from powdered corn (maize) or corncobs, these products lead to dehydration, hypovolemic shock, and death when ingested by target species.  Rodent GI tracts are more susceptible to the dehydration of the corn cellulose and they cannot digest it, leading to death after eating enough over several days.

   1. It is very rarely a concern in our pets because they do not eat a large enough volume.

   2. Sometimes they need help with some dehydration but our pets will usually pass the corn cellulose in feces in a few days and should not be otherwise negatively impacted.

      
      

Please make sure you contact your veterinarian and try to bring the packaging of the poison in with your animal if they have ingested any rodenticide.