Bromethalin Exposure in Dogs and Cats: A 14‐Year Retrospective Study (2010–2023) From the California Animal Health and Food Safety Laboratory System

ABSTRACT Background Bromethalin, a rodenticide, is increasingly used due to restrictions on other rodenticides. Objectives The study aimed to analyze the frequency, demographics, clinical signs, and diagnostics of suspected bromethalin intoxication in dogs and cats. Animals Two hundred twenty‐three cases (249 samples) involving 123 dogs and 100 cats suspected or confirmed to have bromethalin intoxication were submitted to the toxicology laboratory at the California Animal Health and Food Safety Laboratory. Methods This was a retrospective cohort study. Between 2010 and 2023, Liquid Chromatography–Mass Spectrometry was used to detect desmethylbromethalin (DMB), bromethalin's metabolite, in various tissues and serum. Results Cases increased 2.8‐fold from 59 (2010–2016) to 164 (2017–2023). Cats were significantly younger (median 24 months, IQR: 41.5) than dogs (36 months, IQR: 60.0; p = 0.016) and were more likely to have confirmed DMB exposure (60% vs. 25%, p < 0.0001). Submitted samples for analysis were adipose tissue (37%), liver (20%), and brain (19%). Clinical signs included seizures, tremors, weakness, and paralysis. Magnetic resonance imaging (MRI) findings in 17 dogs and cats were consistent with bromethalin intoxication in 77% of cases. Autopsies (33 cases) revealed CNS lesions compatible with bromethalin toxicosis in 2/8 dogs and in 24/25 cats. Conclusions and Clinical Importance Bromethalin exposure is increasingly prevalent in pets. Adipose tissue remains the most reliable sample for diagnosis; cats are more likely to test positive for DMB and exhibit compatible autopsy results. MRI findings can also support the diagnosis. These insights could assist in diagnosing and managing bromethalin intoxication in pets.