Bromethalin Rodenticide Poisonings in Dogs

What is bromethalin rodenticide poisoning?

Bromethalin is one of the most common types of rodenticides currently on the market. It is found in several forms, including hard blocks, soft baits, pellets, worms/grubs, and meal/grain. Dogs are commonly poisoned when they find loose blocks placed for rodent control, or they access the bulk container. Relay toxicity, where poisoning occurs due to ingesting rodents that died from bromethalin, is theoretically possible but not demonstrated experimentally in dogs.

Once ingested, bromethalin is rapidly absorbed from the gastrointestinal (GI) tract and metabolized in the liver to its more toxic form. The primary target for bromethalin and its metabolite is the central nervous system (CNS). It causes depletion of energy in the CNS, ultimately resulting in swelling of various areas of the CNS, including the brain (cerebral edema), leading to severe neurologic signs. Depending on the amount ingested, clinical signs can develop as soon as 2 hours after exposure and as long as 5 days after exposure. 

What are the clinical signs of bromethalin poisoning?

There are 2 syndromes seen with bromethalin toxicosis, dependent on dose: acute convulsant syndrome and delayed paralytic syndrome. 

In sublethal toxic doses, delayed paralytic syndrome develops within 1-5 days of exposure and progresses over 1-2 weeks. This syndrome has a more subtle onset, often starting with mild lethargy and decreased appetite. It progresses to pelvic limb weakness and ataxia and, ultimately, paralysis. Dogs may also develop fine tremors, seizures, abnormal body positioning, and altered brain activity or coma. 

In doses greater than the lethal dose, the acute convulsant syndrome develops within 2-24 hours of exposure. This syndrome is characterized by severe tremors, seizures, hyperthermia, agitation, and running fits. These signs are worsened with stimulation from light and noise. Fortunately, large exposures are required to reach a lethal dose and this syndrome is rare. 

If the dose ingested falls within the lethal dose range, then either syndrome may develop.

How is bromethalin poisoning treated?

There is no antidote for bromethalin, so early decontamination is extremely important. If a dog ingests a toxic dose of bromethalin, promptly inducing vomiting can be lifesaving. After vomiting has occurred, multiple doses of medical-grade activated charcoal are administered over 24-36 hours and intravenous (IV) fluids are delivered to maintain hydration. Close electrolyte monitoring is important to watch for elevated sodium levels. 

If clinical signs develop, mannitol is started to decrease cerebral edema. Clinical signs are then treated with anticonvulsants, muscle relaxants, antiemetics, and GI prokinetics, as needed. 

What is the prognosis for bromethalin toxicosis?

Unfortunately, prognosis is poor to grave if severe clinical signs develop such as seizures, paralysis, or coma. Patients with milder clinical signs may recover after several weeks but may have permanent neurologic damage. If clinical signs can be appropriately managed but there is no improvement after a week, prognosis is poor. 

If you suspect or witnessed your pet ingesting rodenticide, call Pet Poison Helpline, a 24/7 animal poison control center, at 1-855-764-7661 and take your pet to a veterinarian for treatment.

Pet Poison Helpline, an animal poison control center based out of Minneapolis, MN, is available 24/7 for pet owners and veterinary professionals that require assistance treating a potentially poisoned pet. The staff provides treatment advice for poisoning cases of all species, including dogs, cats, birds, small mammals, large animals, and exotic species. As the most cost-effective option for animal poison control care, Pet Poison Helpline’s per incident fee includes follow-up consultations for the duration of the poison case. Pet Poison Helpline is available in North America by calling 800-213-6680. Additional information can be found online at www.petpoisonhelpline.com.