Anticoagulant rodent Poisons
General Information
Warfarin is used as a poison for rodents. During the last decades of the 20th century rodenticides were "improved" to make killing the rodents more efficient. In the process it has made the poisons more dangerous for our pets as well. The toxicity of these drugs are published in medical texts for veterinarians so it is often possible for us to determine whether a toxic dose has been consumed if we know:
The anticoagulant poisons interfere with normal blood clotting and results in fatal hemorrhage. Dogs and cats may eat warfarin disguised in rodents bait or eat rodents poisoned by warfarin. All of the anticoagulant poisons are flavored in a way to make them appeal to rodents. Often this means that dogs and cats will eat them with enthusiasm. Animals that roam freely are commonly poisoned by accident since the owner may not be aware that neighbors have place poison. We have encountered situations where government agencies have placed poison to reduce rodent populations. It is possible for dogs or cats to be poisoned by consuming rodents poisoned with anticoagulant poisons though this is NOT the normal pattern. Though eating small amounts of warfarin is common, fatal poisoning is uncommon because pets must either consume a large single dose or multiple small doses over time. With the newer poisons this IS NOT NECESSARY.
Signs of warfarin toxicity include bleeding in the skin, gums or eyes, and blood in the stools and/or urine. Breathing may be labored and the pet may be depressed. Commonly the signs of poisoning do not develop for a few days after ingestion of the poison due to the mechanism of poisoning. The anticoagulant poisons do not directly cause the blood not to "clot" but rather interfere with the production of clotting factor by the liver.
In general the antidote for toxicity is to overwhelm the effect of the poison thus allowing the liver to produce more clotting factors. If an animal is actively bleeding then giving the antidote will not have any effect until more clotting factors are produced in the liver of the patient. This is why we may need to provide a transfusion of blood or clotting factors from a donor to stop the bleeding until the patient can start to produce it's own. Since many of the newer poisons act for a month or more we may need to give the antidote for a prolonged period of time if the exact chemical is not known.
Having more information we have about the chemical, the amount
consumed and the patient helps us with treatment. Sometimes follow
up testing is necessary to make sure problems with clotting do
not continue after the antidote treatment is stopped.