Rat Poison

During the winter, we see many cases of animals ingesting rat poison. Most of the cases we see are due to ingestion of anticoagulants (warfarin, brodifacoum) rat poisons. It should be noted that there are actually three general groups of rat poisons.

1. Anticoagulants (warfarin, brodifacoum)
2. bromethalin, a neurotoxin
3. cholecalciferol-containing rodenticides

The anticoagulant rodenticides are the most common, and are marketed under many trade names. The mechanism of action of the anticoagulant rodenticides is to deplete vitamin K, which is required for normal blood clotting. Diagnosis is usually based on the owner seeing the pet ingest bait or a rodent that has eaten bait. Rodents that have eaten anticoagulant rodenticides may contain enough chemical rodenticide to poison a dog or cat. If treatment is started early, prognosis is usually good.

Bromethalin is a new nonanticoagulant (Assault, Vengeance) designed to be lethal to rodents after a single dose. The minimum lethal dose for the dog is approximately 21g bait per pound body weight, meaning that a 30 lb dog would have to consume 630g bait (or 15 packs of bait) to receive a lethal dose. Ingestion of rodents that have consumed bromethalin does not cause toxicity in the dog. Thus bromethalin is a safer rodenticide for use where dogs are present than the anticoagulant rodenticides. Bromethalin is a neurotoxin directly affecting the brain and cerebrospinal fluid. Clinical signs associated with ingestion of bromethalin appear about 10 hours post-ingestion and include severe muscle tremors, excitability, running fits, seizures and depression.

The last category of rodenticides is those containing cholecalciferol or vitamin D (Quintox, Rampage, Ortho Mouse-B-Gone, Ortho Rat-B-Gone). As little as 1g bait per pound body weight can cause toxicity in the dog. Young dogs appear to be more sensitive. These rodenticides act by causing vitamin D toxicosis, raising serum calcium levels to dangerously high levels. Clinical signs arise within 18 to 36 hours after ingestion, and include depression, anorexia, increased urination and increased water intake. Muscles are affected by high calcium, and the animal becomes very weak. Heart conduction becomes slowed, and ventricular fibrillation and cardiac arrest may result.

With all of these, immediate treatment is vital.

Please be careful with any of these rodenticides. Place the bait in a location inaccessible by pets or consider using a mechanical type of rodent control such as an old-fashioned mousetrap or the newer nonchemical mouse-motels.