This is Toxicology Tuesday with a Twist. I’m not going to insult you by asking you if rat and mouse poisons are toxic or not. You know they are. What I am going to do is present you with three different types of rodenticides over the next three weeks and ask you the following questions:
What is the toxic principal? (That is, how does it poison – kidney failure, liver damage, etc.)
What signs might you expect to see?
What, if any, treatment is available?
How toxic is it/what is the prognosis? (On a relative scale of Fair - treatable if caught in time, Poor - might not survive even with treatment, or Grave - likely to be fatal even with treatment)
Are you ready for the challenge? Try it; see how much you know, or can guess.
Answer: By far, the most commonly available rodenticides are the anticoagulants. The toxic principal of these agents is to cause depletion of the body's store of Vitamin K. Since this fat soluble vitamin is necessary for the manufacture of several clotting factors, running out of Vitamin K means losing the blood's clotting ability, and the development of bleeding problems. Warfarin was the original product, and is still available, though not common. It fell out of favor because it requires rodents to feed multiple times in order to ingest enough poison to kill them. Those early animals which didn't receive a fatal dose bred, leading to the creation of warfarin-resistant populations. The second generation products, like brodificoum, kill with one feeding, thus eliminating the resistance problem.
It typically takes 3 to 5 days for an animal to run out of Vitamin K, so the signs don't show up right away. Bleeding can be obvious - blood in the urine, stools, or vomitus, bloody nose, bleeding from the gums, excessive bleeding from a minor wound or from clipping a toenail too short - or it can be more subtle. Pinpoint spots of blood under the skin called petechiae may be seen. (Birding note: The Yellow Warbler got his Latin name, Dendroica petechia, from the fine red streaks on his breast.) Bleeding into the joints can cause lameness, internal bleeding may cause shock with no external signs of injury.
In cases of known ingestion, treatment consists of decontamination (induce vomiting, gastric lavage, use of cathartic agents, and administration of activated charcoal) and monitoring blood clotting values. If the blood tests show toxic changes, the pet is started on Vitamin K therapy. If the pet is already symptomatic, Vitamin K treatment is initiated immediately and continues for up to 30 days, while monitoring blood values regularly. Severe cases may need blood or plasma transfusions.
On my "how bad is it" scale, the anticoagulants have a Fair prognosis. With early and aggressive treatment, most pets are likely to survive this poisoning.
Because of the wide variability in the types of anticoagulant agents and the differences in individual pets, it is impossible to give a rule of thumb for how much poison is significant. Take ALL pets who ingest any kind of mouse or rat poison to the vet immediately, and bring the package with you, even if it is shredded or damaged. Important information may still be obtained from the label.
This final question always comes up: What if a cat (or dog) eats a mouse (or rat) who has eaten poison? In the majority of cases, there is not enough of the active ingredient in the rodent to affect the pet, however, barn cats who eat a lot of poisoned mice could accumulate enough poison to develop bleeding problems.