Anticoagulant Rodenticide Poisoning
written by: Kathy Kimmel, DVM
One of the most common phone calls to veterinary emergency clinics is about family pets eating mouse/rat poison. Many owners are understandably panicked. The good news is that the most common forms of these poisons are one of the few poisons with a true antidote and many pets can be saved with proper treatment.
The most common mouse poisons include Warfarin, Bromadiolone, Brodifacoum, Diphacinone and a few others. These are known as the Anticoagulant Rodenticides. There are other forms of mouse and rat poisons on the market but these are more uncommon and include Strychnine, Vitamin D analogs, Bromethaline and Zinc Phosphide. If you need to use mouse poisons and have pets and/or children, the anticoagulant poisons would be the best choices just in case of accidental exposure because these poisons have antidotes. Most of the poisons are blue or green but some can look like grain.
Anticoagulant Rodenticides kill by inhibiting blood clotting. The blood clotting system is very complicated. In a nutshell, there are proteins that assist in part of the blood clotting cascade which require Vitamin K to become activated. These proteins are known as Serine Proteins and are produced in the liver. Inactive Serine Proteins circulate in the blood stream until they are required wherever there is a disrupted blood vessel, which can occur from cuts or scrapes or blunt trauma (bruise). In normal animals, there is enough Vitamin K to allow these proteins to be activated so that they can help stop the bleeding. The Vitamin K is recycled so that there are always stores in the body in case it is needed. Anticoagulant Rodenticides inhibit the recycling of Vitamin K so the body's stores are depleted and therefore the Vitamin K is not available to do its job in stopping bleeding. It takes several days for this depletion to happen and therefore we do not see symptoms for several days after Anticoagulant Rodenticide ingestion.
The symptom of Anticoagulant Rodenticide ingestion is bleeding. How this manifests in an individual animal can vary widely from lethargy and weakness (due to internal bleeding that is not visible externally) to severe external bleeding. We can see blood in the urine, vomit or stool, nosebleeds, coughing up blood, bruising under the skin (which can be difficult to detect in furry animals!) or bleeding from the mouth. If your pet seems weak and lethargic, have a look at the gums. If there is internal bleeding, the gums may be pale or white. It is a good idea to have an idea of what your pets' gums look like normally so you will be able to tell if there is a change.
Testing for Anticoagulant Rodenticide toxicity involves some fairly simple blood tests. The most commonly run tests include testing the clotting times: PT (Prothrombin Time) and PTT (Partial Thromboplastin Time). Sometimes the pet's blood will be sent out to a laboratory for a PIVKA test (Proteins Induced by Vitamin K Antagonism). If both the PT and PTT are abnormal, there is a very high chance of Anticoagulant Rodenticide toxicity. We often also check the PCV (packed cell volume) which is a test for anemia to determine if a blood transfusion may be required.
Treatment for Anticoagulant Rodenticide ingestion varies with the time frame since ingestion. If you see your pet eating the poison, it is important to get to a veterinarian as soon as possible. The pet can be induced to vomit to empty their stomach before the poison gets absorbed into the bloodstream which will prevent bad symptoms from developing. After inducing vomiting, Activated Charcoal is often administered. The Activated Charcoal will stick to the poison and help prevent absorption.
If it has been more than 2 to 4 hours since ingestion, it is likely too late to induce vomiting. In this case, there are two options for treatment. One is to just start the pet on Vitamin K. Vitamin K is the "antidote" to Anticoagulant Rodenticides. The downside of this is that the medication can be expensive and may need to be given for up to 6 weeks. The other option is actually just to wait until 48 to 72 hours after ingestion and then check the PT and PTT. If the clotting times are longer than normal, then the pet will need to start on Vitamin K. If the clotting times are normal, there is a good chance that either the pet did not eat the poison or at least did not eat enough to cause symptoms. This time period is long enough that we can start to see changes in blood clotting times but before the pet actually starts bleeding.
If the pet is already showing symptoms (where ingestion is not observed), treatment will be more involved. If there has not been enough bleeding to cause anemia, we will start the pet on Vitamin K and give a plasma transfusion, which will immediately provide normal proteins to stop any further bleeding. If the pet is anemic (low red blood cell count) then a whole blood transfusion will be required. In these cases, the pet will need to stay in the hospital. In very severe cases your pet may require oxygen supplementation as well because severe anemia reduces the oxygen transportation to the organs.
People often ask what happens if a cat or dog eats a mouse that has been poisoned. Often, if it is just one mouse, the risk of toxicity to the pet is low. However, if the pet is eating multiple mice the risk of toxicity increases. We are very lucky in Alberta that we do not have a problem with rats. Rats can actually eat enough poison to kill many rats before they will show symptoms and are therefore a higher risk to pets.
So if your pet happens to get into mouse poison, please call the hospital as soon as possible. We will advise you on the best options to save your pet's life. If possible, please bring the package in with you so that we can determine the type of poison involved.