Diphacinone Rodenticide Poisoning In A Dog

Mandy writes from Florida: I found my 11 year old 25 pound Pembroke corgi, Dot, standing over open bag of diphacinone (a type of rat poison). Amount consumed unknown but assumed to be small. 30 hours later I took her to local veterinarian who took blood for PT/PTT test and started 25 mg pills twice daily. Questions: is 25 mg too much to be given twice daily? What if she didn’t ingest any, can she overdose on the K1? The veterinarian wants to retest PT in 2 days. I read there is no point in doing this while she is on the K1. How long should she stay on the K1 without toxic effects if she didn’t ingest any?

Mandy, you present some interesting questions.

While I wouldn’t take any comfort in this, diphacinone is a sort of “middle ground” rodenticide, with the range of least toxic beginning with warfarin, first generation, and the greatest toxicities in the second generation rodenticides. Brodifacoum is a commonly-used second generation rodenticide. Diphacinone is a first-generation rodenticide, but is more dangerous than warfarin.

Treatment of all potential rodenticide cases is similar, however, because it is rare that we know exactly which rat poison the patient ingested and rare for us to know how much. When there is risk that more than one type of poison exposure has occurred our focus is on the most toxic.

With the deadly nature of anticoagulant rodenticides most veterinary practitioners aim to be aggressive with treatment. With that in mind, let’s look at Dot’s current regimen:

1. The passage of thirty hours between ingestion and beginning of treatment means that a substantial amount of diphacinone has probably been absorbed into the body. It is too late, at that point, to induce vomiting, as the offending material is well into the small intestine (and probably the large intestine, as well).
2. Many clinicians will begin treatment with an injectable form of Vitamin K1, following up with oral vitamin K1, usually for a minimum of 30 days. Longer treatment is indicated when clotting tests show that negative effects are still present. Vitamin K1 has a very, very wide safety margin in dosing. While the dose you have listed is higher than the upper range I usually use, risks with the oral form are very low. Injectable Vitamin K1 given intravenously, however, is sometimes associated with severe reactions. Your pet’s doctor should not be offended if you ask for an explanation of his dosage choice.
3. Testing PT two days into treatment is a good idea, especially since therapy was late in beginning. Vitamin K1 alone is not a magic antidote. Without help from the liver in forming clotting agents, patients on therapy can continue to bleed, fatally. Testing helps us to know that all systems are working together for an uncomplicated recovery.

In summary, you and your veterinarian are doing all the right things for Dot. Continue to watch her very closely, administer her medications on schedule, and test at the prescribed interval.

Oh, and either get rid of the diphacinone or hide it in such a way that rodents can access it, but pets can’t.

See you tomorrow, Dr. Randolph.

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