Bromethalin – a neurotoxicant
Bromethalin is a commonly used rodenticide, but should NOT be confused with brodifacoum and bromadiolone (which are both anticoagulant rodenticides). Bromethalin, a neurotoxic rodenticide, is marketed under several common brand names of Assault®, Tomcat Mole Killer®, Talpirid®, Real Kill®, Clout®, Fastrac®, Vengeance®, etc.
One of the biggest mistakes I see veterinarians making when treating rodenticides is assuming bromethalin is treated with Vitamin K1 as an antidote. Bromethalin works by uncoupling oxidative phosphorylation in the brain and liver mitochondria.1 This results in decreased ATP production, which affects sodium and potassium pumps; as a result, lipid peroxidation occurs, resulting in sodium accumulation within the cell.1 Edema of the central nervous system (CNS) may result.1
In dogs, the LD50 of bromethalin is 2.38-3.65 mg/kg, with a minimum lethal dose being 2.5 mg/kg.1 Cats are more sensitive to the effects of bromethalin, and the LD50 is significantly lower (0.54 mg/kg).1 Clinical signs are dose-dependent, and the onset of clinical signs depends on the amount ingested. Typically, with acute ingestion, signs may be seen within 2-24 hours.1
Clinical signs of bromethalin toxicity include:
- CNS stimulation or depression
- Abnormal behavior
- Hind limb paralysis
- Changes in the pupillary light reflex (PLR)
- Death (rare)
Treatment includes early decontamination (e.g., emesis induction if asymptomatic, followed by charcoal administration), anti-emetic therapy (to prevent aspiration pneumonia), fluid therapy (to perfuse the patient and the central nervous system), prevention of cerebral edema (mannitol, only if clinical signs are severe), and symptomatic supportive care.
With recent ingestion in an asymptomatic patient, the use of decontamination (e.g., emesis induction, activated charcoal) is warranted. As bromethalin undergoes enterohepatic recirculation, the use of multiple doses of activated charcoal (without a cathartic) can be administered q 6 hours for 24 hours. Patients should be monitored for signs of neurotoxicity.
The use of IV fluid therapy, oxygen support, head elevation, mannitol (to decrease cerebral edema), anticonvulsant therapy, and thermoregulation is warranted if clinical signs develop. The prognosis varies depending on the amount ingested and the severity of clinical signs; however, prognosis is generally fair to excellent with appropriate decontamination and treatment prior to development of clinical signs. If persistent seizures or paralytic syndrome is seen, the prognosis is poorer.
When in doubt, contact the manufacturer of the rodenticide for free Animal Poison Control advice or ASPCA Animal Poison Control Center at (888) 426-4435 for life-saving advice. You can also download the ASPCA APCC app and calculate the toxic dose for bromethalin here!