Rodenticide and Cats: The 3-5 Day Delay and Vitamin K1

Autumn pushes mice indoors, and bait goes down in the same week. Anticoagulant rodenticide is the most common serious poisoning of indoor cats in the colder months, and it is deceptive because nothing happens for 3 to 5 days. By the time a cat is bleeding from the gums, the decision window for decontamination closed days ago. What saves the cat is arithmetic done early: dose, timing, and a vitamin K1 course of 3 to 4 weeks.

Why nothing shows for 3 to 5 days

Anticoagulant baits block vitamin K epoxide reductase, the enzyme that recycles vitamin K. Without it, the liver cannot make clotting factors II, VII, IX and X. Those factors already in the blood keep working until they are cleared, and their half-lives run from about 6 hours for factor VII to 60 hours for factor II. That is why the prothrombin time stays normal for 24 to 72 hours and the first sign, often bleeding gums or a bruise on the belly, appears on day 3 to day 5. Second-generation compounds such as brodifacoum and bromadiolone also bind the enzyme far more tightly and last 4 to 6 times longer, so signs can arrive on day 5 to day 7 and the antidote takes longer to work.

Dose: turning grams of bait into milligrams

Most consumer bait blocks are 0.005 percent active ingredient, which is 0.05 mg per gram of bait. Vets commonly quote a threshold of 0.1 to 0.5 mg of brodifacoum per kg of cat as the point where treatment is started. For a 4 kg cat that is 0.4 to 2 mg, which is 8 to 40 g of bait, and one block is usually 20 to 30 g. A cat that eats a single block is therefore in the range where vitamin K1 is started, not watched. Grain baits are less concentrated but are eaten in larger amounts, and secondary poisoning through a mouse that ate bait is real but requires the cat to eat 2 to 4 mice in a short period.

Rodenticide	Active ingredient	Signs appear	Treatment
First generation	Warfarin, chlorophacinone, 0.005 percent	3 to 5 days	Vitamin K1 for 2 to 3 weeks
Second generation	Brodifacoum, bromadiolone, 0.005 percent	5 to 7 days	Vitamin K1 for 4 to 6 weeks
Cholecalciferol	Vitamin D3, 0.075 percent	12 to 36 hours	No antidote; fluids and calcitonin
Zinc phosphide	2 percent pellets	1 to 12 hours	No antidote; supportive care
Bromethalin	0.01 percent blocks	2 to 4 days	No antidote; brain swelling control

The 2-hour window, and what happens after it

Decontamination only works early. Within 60 to 120 minutes of ingestion, a vet can induce vomiting and give activated charcoal at 1 to 2 g per kg, and that may remove most of the exposure. After 2 hours the bait has left the stomach, and the plan changes to monitoring: a prothrombin time at 48 hours and again at 72 hours, repeated at 96 hours for second-generation products. A cat with a normal PT at 72 hours and no access to more bait is usually cleared. A cat with a prolonged PT starts vitamin K1 whether or not it looks well, because looking well is exactly what the first 3 days look like.

Vitamin K1: the 3-to-4-week course

The standard regimen is 2.5 to 5 mg per kg, split into 2 doses a day, given orally with a fatty meal or by injection for the first day if the cat is bleeding. Duration is not negotiable: 3 to 4 weeks for first-generation products, 4 to 6 weeks for brodifacoum. Stopping at day 10 because the cat looks fine is the classic relapse, and the second bleed is worse than the first. Before stopping, the vet checks a PT 48 hours after the last dose; if it has climbed, the course restarts. Transfusions are for the cat that is already bleeding, and they buy hours, not days.

5 rules for killing mice in a house with a cat

1. Skip poison indoors. Snap traps inside a locked box, or an electric trap, kill a mouse without leaving a toxic carcass that a cat can find under the sofa.
2. If bait is used, it goes in a locked station. Screw-closed, keyed, and placed where a cat cannot fit a head: behind a 2 cm gap is not enough, a cat's skull passes a 7 cm opening.
3. Count the bait. Write the number of blocks and the date on the station, and check it every 7 days. A missing block is an exposure until proven otherwise.
4. Find dead mice within 24 hours. Gloves, bag, bin outside. A cat that eats 2 to 4 poisoned mice is at risk of secondary poisoning.
5. Ask what the neighbours and the building use. Keep the packaging of anything found, because 1 label identifies the compound and the antidote.

Signs, and the ones people miss

Bleeding gums, a nosebleed that lasts more than 10 minutes, bruising on the belly or inner thighs, black tarry stool, blood in urine, a cat that is suddenly weak on the back legs, or breathing at more than 40 breaths a minute from blood in the chest. Pale gums and a heart rate above 200 are late. A cat that is quieter than usual in autumn, eating more and moving less, is also the cat most likely to be exploring the cupboard where the bait is stored, which is the pattern behind the autumn weight gain problem.

What to do in the first 10 minutes

• Take the bait package away from the cat and photograph the label, front and back.
• Estimate how much is missing: count blocks before and after, do not guess.
• Note the time to the minute; the 2-hour window is measured, not remembered.
• Call the vet or a poison line before inducing anything. Never use salt water or hydrogen peroxide.
• Bring the cat, the package and the count to the clinic. Check the compound against the toxic substance list on the way.

Frequently asked