Anticoagulant rat bait does not make a cat bleed on day 1. It blocks the vitamin K cycle in the liver, and the clotting factors that depend on it fade out over 3 to 5 days, so a cat that looks normal at hour 6 can have a nosebleed on day 4. Three numbers decide the case: the dose swallowed in mg per kg, a prothrombin time (PT) drawn at 48 hours, and 4 to 6 weeks of vitamin K1 on prescription.
Why the delay is 3 to 5 days, not 3 to 5 hours
Second-generation baits such as brodifacoum, bromadiolone and difenacoum block the enzyme that recycles vitamin K in the liver. Without recycled vitamin K the liver cannot finish factors II, VII, IX and X. Factor VII has the shortest life at about 6 hours, so PT climbs first, usually by 24 to 48 hours, days before a bruise appears. The bait itself clears from the blood in 2 to 3 days; the block on the liver lasts far longer, which is why pills run for 4 to 6 weeks while the poison is long gone.
Bait is sold at 0.005 percent, which is 50 mg of active ingredient per kg of bait. A 4 kg cat that eats 30 g takes in 1.5 mg, or 0.375 mg per kg. Most vets treat anything above 0.05 mg per kg of a second-generation bait as a case that needs PT monitoring even with no signs. One 20 g block holds 1 mg: for a 3 kg cat that is 0.33 mg per kg, about 6 times the treatment threshold.
First 60 minutes: 4 steps, no kitchen remedies
Do not induce vomiting at home. Hydrogen peroxide at 3 percent burns the stomach lining, and cats vomit unreliably, so the usual result is bait in the lungs instead of the bowl. Vets induce vomiting only when the cat is seen within 1 to 2 hours and is fully alert; past 4 hours the stomach is empty and the effort buys nothing.
Keep the box, the bait station or a photo of the label. The active ingredient and the strength decide the whole plan, and 2 baits that look identical can need different drugs. Weigh the cat on a kitchen scale, count how many 10 g or 20 g blocks are missing, and write down the time. Activated charcoal at 1 to 3 g per kg is a clinic decision, never a kitchen one, and never for a cat that is vomiting or dull.
Skip the human vitamin bottle. Vitamin K3 in pet tonics does not repair the block and can damage red cells at high doses. Vitamin K1 is a prescription drug whose dose and length depend on which bait was eaten.
Which bait, how fast, how long
| Active ingredient | Bait strength | Signs appear | First PT check | Vitamin K1 course |
|---|---|---|---|---|
| Brodifacoum | 0.005 percent | 3 to 5 days | 48 hours | 4 to 6 weeks |
| Bromadiolone | 0.005 percent | 3 to 6 days | 48 hours | 3 to 6 weeks |
| Difenacoum | 0.005 percent | 4 to 7 days | 48 hours | 4 weeks |
| Diphacinone, first generation | 0.005 percent | 5 to 7 days | 48 hours | 2 to 3 weeks |
| Cholecalciferol, vitamin D3 | 0.075 percent | 12 to 36 hours | Calcium and phosphorus, 24 hours | No vitamin K1 |
The last row is the trap. Cholecalciferol bait kills by raising blood calcium, not by blocking clotting, and vitamin K1 does nothing for it. A cat that ate vitamin D3 bait needs fluids and calcitonin, and the lab work is calcium at 0, 24 and 48 hours. Read the label before you accept any plan.
The 48-hour PT and the 2x rule
PT is the test that matters. aPTT can stay normal while PT doubles, so a normal aPTT rules nothing out. Draw a baseline when the cat arrives, then repeat at 48 hours and again at 72 hours. A PT longer than 2 times the top of the reference range confirms anticoagulant poisoning and treatment starts the same day, with or without bleeding. A normal PT at 48 hours after a known second-generation meal is good news, not a discharge: many vets repeat at 72 hours because factor VII can fall late.
Expect 80 to 200 CNY for a PT and 300 to 600 CNY for a full coagulation panel in a city clinic; plasma runs 800 to 2000 CNY per unit. Ask for the result in seconds and keep every report, because a single value says less than the trend across 48 and 72 hours.
Vitamin K1: 4 to 6 weeks, pills not needles
The dose is 2.5 to 5 mg per kg per day, split into 2 doses, given with a fatty meal or a drop of oil because vitamin K1 is fat-soluble. A 4 kg cat at 5 mg per kg needs 20 mg a day, which is two 10 mg tablets every 12 hours. Oral beats injected: IV vitamin K1 can cause anaphylaxis in a small share of cats, so injections are kept for a cat that cannot swallow or is bleeding now.
Length follows the bait, not the cat's mood. Brodifacoum and bromadiolone get 4 to 6 weeks, first-generation bait gets 2 to 3 weeks, and a cat that looks perfect at day 10 does not earn an early stop. Stopping at day 10 is the classic relapse: bleeding returns around day 18 to 25 as the liver store drains again. Recheck PT 48 hours after the last pill, and stop only on that number.
Signs that mean the ER tonight
Pale or white gums, bruising on the inner ear or belly, a nosebleed past 5 minutes, black tarry stool, blood in urine, a swollen joint, or breathing at 40 plus per minute. Any one of these means blood is pooling in a cavity and the window is 12 to 24 hours, not 3 days. A cat down 20 percent of blood volume needs plasma or whole blood; vitamin K1 cannot stop a bleed that is already running. Bleeding into the bladder can also leave a clot that blocks the urethra, and the rules for a cat with a catheter are in urinary catheter aftercare. If a second bait or a chewed houseplant is in the picture, check the ingredient in the toxin lookup before you call.
5 steps for tonight
- 1. Photograph the bait label and weigh the cat.
- 2. Call the clinic and say the ingredient, the strength and the estimated mg per kg.
- 3. Book a PT at 48 hours even if the cat is playing.
- 4. Start vitamin K1 only on a vet's dose, with food, twice a day.
- 5. Recheck PT 48 hours after the final dose before you celebrate.
Frequently asked
My cat ate bait 2 hours ago and seems fine. Can I just watch it at home?
Watching at home is how these cases go wrong, because the first sign may be a nosebleed on day 4 when clotting factors are already below 5 percent of normal. Call the clinic with the label, the strength and your cat's weight, and ask for a PT at 48 hours. If more than 0.05 mg per kg of a second-generation bait was eaten, most vets start vitamin K1 the same day and recheck PT at 48 and 72 hours.
How long does vitamin K1 really need to be given?
For brodifacoum and bromadiolone the usual course is 4 to 6 weeks, and for first-generation bait 2 to 3 weeks. The length is set by the bait, not by how the cat looks, because the liver store drains slowly and a cat that stops at day 10 often bleeds again around day 18 to 25. A PT taken 48 hours after the last dose is the only safe way to stop.
Is one normal PT test enough to rule out poisoning?
No. A single normal PT at hour 6 or hour 12 means little, because factor VII is still falling and PT may not double until 48 hours. Vets repeat the test at 48 and often at 72 hours after a known second-generation ingestion. A normal aPTT is even less useful, since it can stay in range while PT has already doubled.