Is Bromethalin toxic to dogs?

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 dog ate the bait within the last 4 hours and has no signs, the vet may make it vomit, then give activated charcoal to bind the poison in the gut. Because bromethalin cycles between the liver and the gut, the vet may repeat the charcoal every 8 hours for up to two more doses, with IV fluids and a blood sodium check before each dose. 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 may give mannitol to reduce brain swelling, methocarbamol for tremors and anti-seizure drugs, with nursing care for a dog that can't stand. Steroids are unlikely to help. Your dog may need a few days in hospital, and monitoring for at least 24 hours after eating the bait is often necessary.

The outlook is good when treatment starts before signs appear. In a study of 192 dogs that ate bromethalin, the median time to reach the vet was 2 hours, only 25 dogs developed signs and 187 survived to discharge. The outlook was excellent unless severe signs appeared, and those carried a high euthanasia rate. 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 dogs 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.