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Rat Poisoning (anticoagulant rodenticide)
J.C. Hardin, DVM
There are several kinds of poisons used to kill rats and mice. The following pertains only to those poisons that prevent blood clotting. These kinds of poisons are called 'anticoagulant rodenticides'. They kill rats and mice by making them bleed to death internally. The poison acts on the liver to bind up an enzyme that converts vitamin K from an inactive form to an active form. Vitamin K is needed for blood to clot. In pets, signs of rat poisoning don't usually appear until one to three weeks after the pet has eaten the poison. It takes this long for the body's store of active vitamin K to be depleted. When this supply runs out, the rat poison has caused the liver to be unable to replace it, and internal bleeding begins. If a pet is seen eating the rat poison and taken to a veterinarian quickly, chances are very good no problems will occur. The pet will usually be made to vomit with an injection of apomorphine. (Drowsiness may occur after this shot). Once the vomiting has stopped, activated charcoal is usually given to bind up any remaining poison residue in the stomach. Some pets are too aggressive or fearful to allow charcoal to be given by mouth, and some of these refuse to eat it when it is mixed with food. In these cases, the charcoal is either simply not given, or the pet is anesthetized and the charcoal is given by a stomach tube. Vitamin K1 is usually prescribed and must be given for one to three weeks. The human form of vitamin K1 (mephyton) is very expensive. The veterinary form is very inexpensive. It is best not to ask for a written prescription for vitamin K1 from a human pharmacy - for some pets, a three week supply would cost more than $1500 from a human pharmacy, and less than $100 from a vet's office. It is important not to give vitamin K2 (plant source) instead of vitamin K1. Vitamin K2 is available at many health food stores, but is not adequate for treatment of rat poisoning. The veterinarian may want to do a blood clotting test even if you saw your pet eat the rat poison that very day. Again, though it takes one to three weeks after eating the poison for bleeding problems to occur, consider the possibility that your pet may have eaten some of it previously without your knowledge. If this occurred, then a bleeding disorder may already exist in your pet. If so, immediate hospital care is needed. It is important to watch for signs of internal bleeding for several weeks after a pet has ingested rat poison. Watch for bruising in the skin (ecchymoses), especially on the abdomen or inside the ears. Watch for pinpoint hemorrhages (petechia) in the gums. Watch for pale gums, that may indicate anemia from blood loss (compare the gum color to the color of the tooth, unless the gums are highly pigmented (Chows and Shar Pei's for instance). The gum should be distinctly pink compared to the tooth color. (For dogs with pigmented gums, look at the mucous membranes inside the penile sheath or vulva.) Watch for coughing or labored breathing that may indicate bleeding into the lungs (this is often the first symptom seen). Watch for black stools that may indicate intestinal bleeding, but REMEMBER that any pet given activated charcoal will have black stools for a day or two as the charcoal is passed. If black stools are seen starting four days after the charcoal is given, then intestinal bleeding must be considered. Watch also for nosebleeds, vomiting of blood (coughed up from the lungs and swallowed), and a blood color to the urine. Watch for lameness - some dogs bleed into their joints after rat poisoning and will limp around as a result. To help prevent bleeding, don't let pets who have ingested rat poison exercise vigorously or be handled roughly. Exertion and rough handling cause small breaks in blood vessels that will not stop bleeding as they would in a normal animal. Big bruises and other signs as listed above can result. Any pet with a bleeding disorder from rat poison needs aggressive emergency and intensive care. Plasma transfusions are given to replace clotting factors. Oxygen is usually needed, sometimes for several days. Of course, vitamin K injections are started quickly too. Whole blood or red cell transfusions are needed if anemia is present. Some patients have too much internal damage from bleeding to be saved. Others do recover with intensive care.