Rodenticides: A Threat For More Than Just Rodents

Most people have had the experience of hearing little footsteps on our roof or catching a tail at the flash of light in your garage. You might not necessarily be sure whether it is a mouse, a rat or something else, but all you know is that it does not belong in your house and needs to disappear.

The occurrence of rodents prompts people to go to the nearest shop and buy rat poison or set a mouse trap with bait, without thinking about the consequences. Some of us might search online for an eco-friendly version, but this might not always mean that it is not dangerous and deadly to nature. Pets (and other animals like owls) can easily ingest rat poison by accident or eat an animal like a rat that might have ingested the poison, possibly causing their death.

“The majority of poisonings are from consumption of the bait itself (or primary poisoning). There is very little risk of poisoning from eating a single poisoned rat, but in animals that frequently consume rats, the risk of secondary poisoning is much higher,” says Dr Travis Gray of the Cape Animal Medical Centre (CAMC).

Rat and mouse poisons (rodenticides) are not all the same. There are four common active ingredients in these poisons:

  • Long-acting anticoagulants
  • Cholecalciferol
  • Bromethalin

“Each has a different mechanism of action of poisoning, and not all are treated with Vitamin K1. It is important to make sure you and your veterinarian have correctly identified the active ingredient in the product ingested to make sure treatment for your pet is appropriate. “Of course it is also advisable to check with your vet which rat poisons to use if you really need to,” says Dr Omar Mehtar of TAH Somerset West.

Dr Mehtar explains, “The most common rodenticides cause internal bleeding, brain swelling, or hypercalcemia (high calcium level, which can lead to things like kidney failure). All of these are fairly treatable, if they get the animal to the appropriate vet immediately, and arm the vet with the right information, like what rat poison was used, how long ago the dog ate it and how much. “The vitamin D toxicity appears to be the worst and a dog would need hospitalisation and a battery of bloods tests done daily for a number of days. The prognosis is guarded depending on which one the dog ate, how much they ate and how shackled the vet is in terms of treatment. The dosage of poison usually determines toxicity. All of these can cause toxicity, especially since dogs tend to guzzle down the baits rather than stick to one kibble.”


Long-acting anticoagulants (LAACs) are the most common and well-known type of mouse and rat poison. This type of poison prevents the blood from clotting, resulting in internal bleeding. LAACs work similarly to the ‘blood thinner’ medications that people take (like Warfarin or Coumadin). When dogs or cats ingest LAACs, it typically takes 3-5 days 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 include signs of internal bleeding: lethargy, exercise intolerance, coughing, difficulty breathing (due to bleeding into the lungs), weakness, and pale gums. Less common signs include vomiting, diarrhoea (with or without blood), nose bleeds, bruising, bloody urine, swollen joints, inappetence, and bleeding from the gums.

“A common misconception amongst pet owners is that if the patient isn’t showing any clinical signs, then they must be alright. The problem is that the anticoagulant rodenticides can be silent killers. Fluffy could be wagging his tail and eating well, but bleeding internally while he does so. This makes it important for owners to always be vigilant, and to check the poison routinely to make sure none of the household has gotten hold of it,” warns Dr Gray.


Over-the-counter medications or food with high vitamin K content will not be sufficient substitutes. Most pets need to be treated with Vitamin K1 for 30 days. Two days after the last dose of Vitamin K1 is administered, a blood clotting test called a prothrombin (PT) should be checked to make sure the clotting is normal; otherwise, your pet can still potentially bleed out despite one month of therapy. Vitamin K is, however, expensive and is size dependant.

“Anticoagulant rodenticide toxicities are still the most common poisonings we see at CAMC,” says Dr Travis Gray of CAMC. The survival rate is good, with appropriate treatment. I concur with my colleague, Dr Mehtar that the cost of the antidote (vitamin K) is often the prohibitive factor. Blood transfusions, or plasma transfusions can also add significantly to the cost of treatment,” he adds.


Cholecalciferol is one of the most potent mouse and rat poisons on the market. When ingested in toxic amounts, cholecalciferol, or activated vitamin D3, can cause life-threatening elevations in blood calcium and left untreated can result in kidney failure.

Dr Gray adds that they are seeing an increase in the number of cases of Cholecalciferol-containing rodenticide toxicities at CAMC. “Of the cases I’ve treated, all presented within hours of ingestion of the poison. If the patient presents once the kidneys are damaged or calcified, the prognosis is poorer. Any calcification of the kidneys is unfortunately permanent,’ he says.

 Common signs of poisoning may not be evident for 1 to 3 days, when the poison has already resulted in significant and potentially permanent damage to the body. Increased thirst and urination, weakness, lethargy, decreased appetite, and vomiting may be seen. Acute kidney failure usually develops 2-3 days after ingestion of this type of mouse and rat poison.

Antidote/Treatment: There is no known antidote for Cholecalciferol poisoning. The most challenging poisoning cases to treat as long hospitalisation, frequent laboratory monitoring, and expensive therapy is often required for a positive outcome. Cholecalciferol has a very narrow margin of safety, which means that even small ingestion of this poison can result in severe clinical signs or death. Toxic ingestions must be treated quickly and appropriately to prevent kidney failure.


“Bromethalin causes swelling of the brain which results in neurological symptoms when ingested in toxic amounts. Symptoms include lethargy, weakness, incoordination (ataxia), tremors, seizures, paralysis, and eventually death. The timeframe for Bromethalin poisoning varies from a few hours to a few days,” says Dr Mehtar.

Antidote/Treatment:  There is no known antidote to Bromethalin poisoning. It can cause serious and long-lasting effects. Treatment includes decontamination, IV fluids, and specific drugs to decrease brain swelling. Cats are more sensitive to Bromethalin than dogs. As this type of mouse and rat poison has a narrow margin of safety and no antidote, prompt therapy is often needed in all species.


Phosphides are found in certain types of mouse and rat poison or in mole baits. It works by releasing deadly phosphine gas, which is produced when the poison mixes with stomach acid. Food in the stomach will increase the amount of gas produced and, therefore, increase the toxicity of phosphide poisoning. Do not feed your dog or cat after they have ingested this type of poison.

Dr Gray says, “We’ve had one Zinc Phosphide toxicity and unfortunately the patient died. The survival rate of such poisoning is incredibly low, even with optimal treatment. To make matters worse, the gas produced once the poison has been ingested, is also toxic to humans, making treatment dangerous for the owners and hospital staff.”

Symptoms of Phosphide poisoning include drooling, nausea, stomach bloating, vomiting, abdominal pain, shock, collapse, seizures, liver damage, lung damage, and even death.

Antidote/Treatment: Dr Mehtar advises the administration of antacids (e.g. Maalox®) soon after ingestion to help to decrease the amount of gas produced. Please be aware that phosphine gas poses a threat to people also, so inducing vomiting is best done by veterinary professionals (instead of pet owners) in a well-ventilated area or outdoors. If your dog vomits on the way to the veterinarian, make sure to open your car windows (safely) or turn on the airconditioner so the gas doesn’t poison you as well. Inhalation of the fumes from your pet’s vomit may cause lung irritation to both you and your pet.

Rodenticides have the potential to cause great harm, and even though most of them do have effective treatment strategies, the treatment will be expensive (several thousand rand usually) and offers no guarantee of survival. “Ensure that poisons are inaccessible to pets – keeping in mind that pets can be very resourceful when they want to get hold of something!” adds Dr Gray.

“Never give home remedies like milk or food without consulting a veterinarian or Pet Poison Helpline specialist first. Likewise, never induce vomiting in your dog or cat without consultation, as it can be more dangerous to your pet,” advises Dr Mehtar.

“If your pet has ingested rat poison, always try and bring the packaging of the poison you use so the vet can identify the active ingredient and treat the pet appropriately. I have to stress that no poison is pet safe, regardless of what the marketing team tells you. The only form of rat and mouse control that I would recommend would be speaking to the EcoSolutions who will advise on owl boxes for your property. Owls are excellent rat and mouse catchers and do very well in urban environments if encouraged to nest and stay,” concludes Dr Omar.




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