Bromethalin (a brain-swelling rodenticide) in Pets

Bromethalin rat bait causes brain swelling, and cats are especially sensitive. Compare mg/kg with Merck's LD50 (0.4–0.71 mg/kg cats, 2.38–5.6 mg/kg dogs) and learn the two patterns of signs.

What It Is

Bromethalin is a rodenticide that uncouples energy production in nerve cells, causing fluid to build up in the brain and spinal cord. Unlike anticoagulant baits it does not cause bleeding, and vitamin K does not treat it. There is no specific antidote.

Where Pets Come Across It

Green or blue bait blocks, pellets and soft baits sold for mice and rats, which often look identical to anticoagulant baits. Its use has grown since restrictions were placed on some anticoagulant products in the United States.

Which Animals Are Affected

Cats are extremely sensitive, dogs moderately so. Birds and other pets are also at risk.

Published Toxic Dose

The Merck Veterinary Manual gives an oral LD50 of 0.4–0.71 mg/kg in cats and 2.38–5.6 mg/kg in dogs. Doses near or above the average dog LD50 (about 3.5 mg/kg) can cause a convulsive syndrome within 4 to 36 hours, while lower doses can cause a slower paralytic form over 1 to 5 days. Baits commonly contain 0.01% bromethalin, or 0.1 mg per gram.

Signs and How Soon They Appear

High doses: severe tremors, overheating, hyperexcitability, running fits and seizures within 4 to 36 hours. Lower doses: wobbliness, weakness or paralysis of the hind legs, and depression over 1 to 5 days. Signs can last for weeks.

What to Do Right Now

Call a poison line or vet immediately and have the bait packaging or EPA registration number ready, because bait colour does not tell you the ingredient. Early decontamination by a vet is the main treatment. Do not induce vomiting at home.

Frequently Asked Questions

Sources and References

• Merck Veterinary Manual: Bromethalin Poisoning in Animals
• Pet Poison Helpline: Bromethalin

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