Is Bromethalin toxic to cats?

Bromethalin causes swelling of the brain (cerebral edema) which leads to severe neurological dysfunction and potential death.

There is no antidote, and the key to treatment is early, aggressive decontamination. If your cat ate the bait within the last 4 hours and has no signs, the vet may make it vomit with a prescription drug, then give activated charcoal, sometimes in repeated doses. The ASPCA notes that repeated charcoal may not help cats as much as dogs. ASPCA Poison Control's 2003 guidance sets the plan by the dose eaten and the time since, and says to treat at the most aggressive level when the amount is unknown. If signs appear, vets treat brain swelling, tremors and seizures and give supportive care, including feeding support and nursing care for a cat that can't stand. Steroids are unlikely to help. Your cat may need a few days in hospital.

The outlook is best when treatment starts before signs appear. Once signs start, recovery can be slow: they may last for weeks, and in rare cases mild signs are permanent. Mild signs such as back-leg weakness may fade with time, but cats with paralysis or seizures generally have a poor to grave prognosis.

• Mouse and rat baits, sold as blocks, soft baits, pellets and other forms. Their strength ranges from 0.01% to 0.025% bromethalin, which means 0.1 to 0.25 mg of bromethalin in each gram of bait.
• Ready-to-use bait stations sold in stores for home use. In the US, these consumer products may no longer contain second-generation anticoagulants such as brodifacoum, bromadiolone, difenacoum and difethialone, and bromethalin is one of the poisons they use instead. Since these rules took effect, bromethalin has become the rodenticide pets are most often exposed to, according to the Merck Veterinary Manual. A California veterinary laboratory received 2.8 times as many suspected bromethalin cases in dogs and cats from 2017 to 2023 as from 2010 to 2016 (164 against 59).
• Bait put out in homes, garages, stables, farms and even parks: rodent baits are used anywhere there might be rodents.
• The name looks like the anticoagulant baits brodifacoum and bromadiolone, so bromethalin is easy to mistake for one. It is a different poison: it makes the brain and spinal cord swell, it doesn't cause bleeding, and vitamin K1 doesn't treat it.
• You can't tell bromethalin bait from other baits by its color or shape. The active ingredient on the label tells you, and if it isn't clearly visible, the EPA registration number (EPA Reg. No.) on US products lets a poison line identify it.

• Use bait only inside the bait station it comes with, and place stations only where pets can't reach them.
• Store rat and mouse poisons in a locked cupboard or shed, never next to food or pet food.
• Write down how much bait you put out and where, and check often that none has been moved.
• Keep the original package or receipt for as long as the bait is in use, so the active ingredient can be identified quickly.
• Remove dead rodents promptly so your pets can't eat them.