By Dr. Becker
Long-acting anticoagulants, called LAACs, are the most common type of mouse and rat poisoning in use today. Typical active ingredients in these products include brodifacoum, diphacinone, warfarin, and bromadiolone, among others. Most of these products contain green dye so humans can recognize them quickly. But since dogs and cats have poor color vision, the pellets may look like dry pet food.
When ingested by an animal, anticoagulant agents block the synthesis of vitamin K, an essential component for normal blood clotting. This reduces production of certain clotting factors. There is no effect on clotting factors already in circulation in the bloodstream, which is why there is a lag time between ingestion of the poison and bleeding problems. The eventual result, however, is spontaneous and uncontrolled bleeding, which leads to death.
Causes and Types of Anticoagulant Poisoning
The most common cause of anticoagulant poisoning in pets is ingestion of rodent poison. Dogs and cats who go outdoors frequently are at risk for encountering the poison in a neighbor’s yard, in an alleyway, or in a trash bag. Pets that chase and kill rodents can also be at risk. Keep in mind that even if rats or mice aren’t a problem where you live, rodent poison may also be used for other animals such as opossums, raccoons, or squirrels.
Another cause of anticoagulant poisoning is the accidental ingestion of human medications, for example, heparin, which is used to treat certain blood clotting disorders.
Common anticoagulant chemicals found in rat and mouse poisons include warfarin, hydroxycoumadin, brodifacoum, bromadiolone, pindone, diphacinone, diphenadione, and chlorohacinone. Products containing warfarin and hydroxycoumarin are cumulative poisons, meaning they require multiple feedings over several days to kill a rodent. The other listed anticoagulants are deadlier and are intended to kill rodents in a single dose. Rodenticides containing brodifacoum and bromadiolone, for example, are from 50 to 200 times more toxic than those containing warfarin or hydroxycoumarin.
Symptoms in Dogs and Cats
When a dog or cat ingests an LAAC, it usually takes 3 to 5 days before signs of poisoning become obvious. In cases of chronic exposure, however, symptoms can appear sooner.
Common symptoms are signs of internal bleeding or blood clotting issues. They include lethargy, exercise intolerance, coughing, and difficulty breathing due to bleeding into the lungs, a swollen abdomen from accumulation of blood, weakness, and pale gums.
There can also be vomiting or diarrhea (sometimes bloody), bleeding from the rectum, spontaneous nosebleeds, and bruising that appears suddenly without trauma. Other symptoms can include bloody urine, swollen joints, loss of appetite, and bleeding gums or other bleeding in the oral cavity.
Signs of bleeding in more than one location are a definite clue there’s a problem with blood clotting.
Diagnosing Anticoagulant Poisoning
My very first case of LAAC poisoning was in a Husky who was brought in with ruptured blood vessels in her sclera, which are the white parts of the eyes. When I looked at her beautiful blue eyes, all of the area around the blue was flaming red instead of white, and looked really scary.
When I checked her gums, they were very pale, and she also had petechial hemorrhages that looked like tiny speckles all over her mouth. They were actually hundreds of broken blood vessels just under the mucus membranes.
The skin on the dog’s belly was also starting to show some bruising. With signs of bleeding in more than one location on her body, I knew there could be a problem with blood clotting caused by anticoagulant toxicosis.
If you suspect your pet has ingested rodent bait or another product containing an anticoagulant, you’ll need to give a thorough history of his health and recent activities to your veterinarian. A chemical blood profile, complete blood count, and urinalysis will be performed.
Your vet will also check the time it takes for your pet’s blood to clot to determine the severity of the poisoning. The PTT (partial thromboplastin time) test looks at intrinsic pathways. The PT (prothrombin time) test measures extrinsic pathways. If both pathways show disruption, rat poison is the most likely cause.
If you have a sample of the suspected poison, you should take that with you to your veterinarian's office. Samples of your dog’s stool and/or vomit may also be helpful.
Treatment for Anticoagulant Poisoning
If your pet has just ingested the poison, the veterinary staff will likely attempt to induce vomiting, and certain agents will be administered to prevent the poison from entering your dog’s or cat’s system.
If an animal is suffering from significant blood loss from spontaneous bleeding caused by anticoagulants, he or she will receive fresh whole blood or a frozen plasma transfusion, and require hospitalization.
The antidote to anticoagulant poisoning is vitamin K. It is started by injection in life-threatening situations. When the patient is stabilized, oral tablets are prescribed. Veterinary-strength vitamin K is a 25 mg tablet, which is actually 5 times the strength of the oral human prescription dose.
Vitamin K1 is the form of vitamin K that’s used for therapeutic purposes. It’s a natural form of vitamin K found in plants and is absorbed nutritionally. Vitamin K3 might seem like an inexpensive way to treat a pet with rat poisoning at home, but vitamin K3 is sometimes toxic and can lead to red blood cell destruction. Inexpensive, over-the-counter vitamin K3 pills are not acceptable antidotes, and I don’t recommend that you try them. Vitamin K1 is absorbed early in the GI tract and concentrates directly in the liver where it is most needed. Only vitamin K1 should be considered as the antidote for anticoagulant rodenticide poisoning.
Since there are different classes of anticoagulant rodenticides and they remain in the animal’s body for different periods of time up to several weeks, it can really be difficult to determine when to discontinue vitamin K therapy. Common practice is to give the therapy for a couple of weeks, discontinue it, and then run the PT test after 48 hours. If the poison remains in the animal’s system, the PT test results will be abnormal but the bleeding will not have restarted yet.
The PT test results tell your veterinarian whether or not additional vitamin K therapy is needed. When the PT test has returned to normal, you know it’s safe to discontinue therapy. It’s extremely important, after vitamin K therapy is discontinued, to return for the PT recheck as scheduled, because just an extra day or two will allow internal bleeding to recur if your animal hasn’t had enough therapy.
Other Toxic Rodenticides
While anticoagulant rodenticide poisoning can threaten the life of your pet, there is at least an antidote readily available (vitamin K).
Other types of mouse and rat poison have no known antidote at this time, including Vitamin D Analogs (Quintox, Rampage, Rat-B-Gone, and Mouse-B-Gone), bromethalin (Fast Kill), strychnine (gopher bait), and zinc phosphide in gopher bait such as Moletox. I’m sad that these really scary rodenticides are available on the market, because there’s no hope for animals that accidently ingest them.
What if My Pet Eats a Poisoned Rodent?
If your dog or cat eats a rat that has gorged on a fast-acting anticoagulant rodenticide, there is certainly cause for concern. A rat with a big appetite can eat enough poison to kill 20 rats before he starts to feel sick. If your pet eats that rat, all the poison will be transferred right up the food chain to your pet.
Fortunately, most rats don’t overeat or gorge themselves to this degree, and animals that are secondarily poisoned by eating a poisoned rat usually depend heavily on rats as their main food source. Probably none of you listening or reading here today are allowing your pet to free-range hunt in your front or backyard or other property. If you are for some reason doing that, I strongly encourage you to stop now.
Bottom line, if you think your pet has consumed any type of poison or an animal that may have consumed poison, you need to visit your veterinarian as soon as possible for a coagulation test. Even if your pet appears fine at the moment, you should still go and get the test. By the time a dog or cat begins to show symptoms of toxicity, things can progress very rapidly. Early detection and treatment is always the smartest choice, and the one with the most favorable outcome.