Vitamin D Poisoning in Cats: Calcium Spike

Vitamin D is the most deceptive poison on the shelf, because the first 6 hours usually look like nothing. Cholecalciferol pulls calcium out of bone and out of the gut at the same time, and the resulting calcium-phosphate load crystals out inside the kidneys. A 4 kg cat that eats 3 g of 0.075% rodent bait swallows about 2250 micrograms, roughly 560 micrograms per kg, well past the 100 to 500 micrograms per kg range where cats get sick. Get the number, then get to a clinic before the 12 hour mark, even if the cat is eating normally.

Where the vitamin D is hiding

Rodenticide bait is the classic source and the most concentrated: 0.075% cholecalciferol means 750 micrograms per gram of bait, so a 20 g block carries 15,000 micrograms. The second source is the medicine cabinet. A 1000 IU capsule holds 25 micrograms, a 5000 IU capsule holds 125 micrograms, and a 50,000 IU prescription capsule holds 1250 micrograms;cats are small enough that 2 or 3 high-dose capsules matter. Third come pet supplements, cod liver oil, and vitamin drops meant for children, which are often dosed per drop at 400 IU, or 10 micrograms. Fourth are plants of the Solanum group, which carry a weak vitamin D analog and are a minor risk compared with the first three.

Bait comes in 2 chemical families, and the anticoagulant type works by a completely different route; our guide to rat poison and vitamin K covers that one, and the poison dose tool turns a label into a milligram-per-kilo number you can read to a vet.

Why calcium and phosphorus rise together

Cholecalciferol is converted in the liver to 25-hydroxyvitamin D, then in the kidney to calcitriol, the active hormone. Calcitriol does 3 things at once: it pulls calcium and phosphorus out of bone, it increases absorption from the intestine, and it tells the kidney to keep calcium instead of dumping it. Blood calcium can climb from a normal 9 to 10.5 mg/dL to 14 mg/dL or higher, and phosphorus follows. Above roughly 16 mg/dL, calcium phosphate precipitates in the renal tubules, the basement membranes of the kidney mineralize, and acute kidney injury starts. That is why a cat can look fine at hour 6 and be in kidney failure by hour 48.

The 6-hour line

Six hours is the first decision point, not the finish line. Vomiting and drooling often begin between 6 and 12 hours, and a blood panel drawn at 6 hours can still be completely normal, because the liver has not finished converting the dose. Use the 6 hour mark for 2 things only: to confirm decontamination is still worth doing, and to establish a baseline calcium and phosphorus so the next panel has something to compare against. If the cat ate bait less than 2 hours ago, a vet may give activated charcoal; after 6 hours the charcoal has almost nothing left to bind. Repeat blood work at 24 and 48 hours is what actually rules the poisoning in or out.

Two tests that decide the case

The first test is ionized calcium, which measures the active fraction rather than the total, and it is the number that tracks symptoms. The second is phosphorus, because a rising phosphorus with a rising calcium is the signature of vitamin D toxicosis rather than of a tumor or a parathyroid problem. A renal panel (BUN, creatinine, SDMA) and a urine specific gravity run on the same sample show whether the kidneys are already affected, and an abdominal radiograph can find bait in the stomach if the cat ate a block rather than pellets. Total calcium alone is not enough; it misses the cases where protein is low and the ionized fraction is high.

How much is too much

Source	Amount eaten	Vitamin D3	Risk for a 4 kg cat
0.075% bait block	1 g	750 mcg	Below the toxic line, monitor 24 hours
0.075% bait block	3 g	2250 mcg	560 mcg/kg, expect high calcium
5000 IU capsule	2 capsules	250 mcg	62 mcg/kg, usually mild
50,000 IU capsule	1 capsule	1250 mcg	312 mcg/kg, vet visit today
Vitamin D drops, 400 IU	5 drops	50 mcg	12 mcg/kg, mild, watch 24 hours

Signs, in the order they appear

Hour 6 to 12: vomiting, drooling, loss of appetite, and a cat that hides. Hour 12 to 24: increased thirst, urinating more and larger volumes, weakness, and a stiff gait. Hour 24 to 48: dehydration, lethargy, tremors, a slow heart rate, and in severe cases seizures or sudden death from arrhythmia. Any cat with vomiting plus increased drinking after possible bait exposure needs blood work today, not in 3 days. Cats with kidney disease, or on a high vitamin D diet, go down faster.

Treatment and what it costs you to wait

Care is hospital-based and prescription-only: intravenous saline to push calcium into the urine, furosemide to increase calcium excretion, prednisolone, and in serious cases calcitonin or pamidronate to block calcium release from bone. All are given by veterinary prescription, and none can be dosed at home. A cat treated within 6 to 12 hours usually needs 2 to 4 days of fluids; a cat that arrives in kidney failure may need 5 to 7 days and still lose kidney function permanently. Cost is driven by the length of the fluid run, not by the antidote.

Prevention that holds up

• Use traps or snap traps indoors instead of cholecalciferol bait, or ask a pest service for bromethalin-free, vitamin D-free options.
• Keep every supplement bottle in a latched box, and never leave a weekly pill organizer on a counter overnight.
• Store bait blocks in the original sealed container and count them before and after each placement.
• Write the product name, the concentration, and the amount missing on a card and keep it by the phone.
• If the cat may have eaten bait, book the 6 hour panel and the 48 hour recheck on the same call.

Terms mentioned in this article

BUNSDMA

Frequently asked

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