Poisonings from ingesting rodenticides are one of the most common types of toxicities seen in veterinary practices in both small and large animal species. (Note: Relay toxicosis—poisoning from eating rodents killed by rodenticides—does not commonly occur but is possible and may also be seen in wild predators and birds of prey that ingest poisoned rodents.) There are many different types of mouse and rat poisons available today, and they come in a wide variety of colors and formulations. Accurate identification of the active ingredient in these poisons is the first step for veterinarians to be able to provide effective treatment, because the ingredients vary dramatically in toxicity and mechanism of action. These poisons cannot be identified based on color or shape alone and are best identified by looking at the packaging for the name of the active ingredient or the EPA registration number. Here are the four most common active ingredients in rodenticides, their effects, and how veterinarians treat them.
1. Long-acting anticoagulants
Rodenticides containing long-acting anticoagulants as the active ingredient are the most common and well known type of mouse and rat poisons.
Mechanism of action: This type of poison works by preventing the blood from clotting, leading to internal bleeding. It will typically take at least 48 hours before this type of poison takes effect. However, if the pet has been chronically exposed to the product, the onset of clinical signs may be earlier.
Common signs and symptoms of poisoning: Lethargy, exercise intolerance, coughing and difficulty breathing (due to pulmonary bleeding), weakness, and pale gums are the most common and result from internal bleeding. Less common signs include vomiting and diarrhea (with or without blood), nosebleeds, bruising, bloody urine, lack of appetite, and bleeding from the gums.
Antidote and treatment: Fortunately, this poison does have a readily available prescription antidote called vitamin K1. Treatment for at least three to four weeks is necessary. Over-the-counter medications or food with high vitamin K content will not be sufficient substitutes.
Threat: The toxicity of long-acting anticoagulants will vary greatly among active ingredients with brodifacoum being one of the most potent. The signalment of the patient also may be a factor when determining a toxic dose because animals with underlying liver or gastrointestinal disease, as well as the very young or very old, are more at risk. Certain species, such as cats, are more resistant to the effects of long-acting anticoagulants and rarely suffer poisoning. Dogs, on the other hand, can be quite sensitive and often require veterinary intervention.
2. Cholecalciferol (vitamin D3)
This is one of the most dangerous mouse and rat poisons on the market and it seems to be gaining in popularity.
Method of action: This poison works by continuously increasing the calcium and phosphorus levels, which can result in secondary kidney failure.
Common signs and symptoms of poisoning: Animals may experience increased thirst and urination, become weak and lethargic, and have a decreased appetite within the first 24 hours after ingestion. Acute kidney failure is typically noted two to four days after ingestion.
Antidote and treatment: This can be one of the most challenging rodenticides to treat, because extensive therapy and laboratory monitoring, which can be costly, is required for a positive outcome. There is no specific antidote, but poisoning does respond to several prescription therapies such as IV fluids, furosemide, calcitonin, and bisphosphonates. Aggressive treatment and frequent monitoring of blood work (calcium, phosphorus, and kidney values) is often needed for a period of two to four weeks after ingestion.
Threat: Ingesting only a small amount of this poison can be potentially fatal for any animal, thus, almost all ingestions may prove toxic.
This is a dangerous poison with a name that is often mistaken for an anticoagulant.
Method of action: Bromethalin works by uncoupling oxidative phosphorylation in the brain and liver mitochondria and can result in cerebral edema (swelling of the brain) when toxic amounts are ingested.
Common signs and symptoms of poisoning: Cerebral edema may result in ataxia (incoordination), tremors, seizures, paralysis, and eventually death. The onset of clinical signs will be dose-dependent and range from two to 24 hours.
Antidote and treatment: In-hospital care for three to six days may be needed since this poison has long-lasting effects. Treatment consists of head elevation, mannitol, and other measures to reduce brain swelling.
Threat: Cats are more sensitive to the effects of bromethalin than dogs; however, the toxic dose for both animals is very small.
4. Zinc, calcium, and aluminum phosphides
These are more commonly found in mole or gopher baits, but they also may appear in some mouse and rat baits.
Method of action: This poison, once in the stomach, releases toxic phosphine gas. Food in the stomach also will increase the amount of gas produced and, therefore, increase the toxicity of the poison. Thus, feeding the patient after ingestion is not recommended.
Common signs and symptoms of poisoning: The gas produced by this poison can result in gastric distension and bloating, vomiting, abdominal pain, shock and collapse, and liver damage.
Antidote and treatment: This poison also does not have an antidote, and veterinarians should perform aggressive decontamination such as gastric lavage. During decontamination, great care needs to be taken to prevent hospital personnel from being exposed to the gas, since it is a potent respiratory irritant. Given the potential risk this gas poses for people, vomiting is best induced by veterinary professionals (not pet owners) in a well-ventilated area or outdoors.
Threat: The toxic dose is very small and nearly all patients ingesting this poison need to be examined by a veterinarian to determine if treatment is necessary.