Rodenticide Risks Rising: Bromethalin Poisoning on the Rise in Dogs and Cats

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

Sigal Klainbart, Marcos Pérez-López, Michael S. Filigenzi, Robert H. Poppenga

Background
Bromethalin is a neurotoxic rodenticide increasingly used in the U.S. following restrictions on anticoagulant rodenticides. Its mechanism involves uncoupling oxidative phosphorylation, causing ATP depletion and white matter edema. Despite known laboratory toxicology, large-scale clinical data on bromethalin exposure in pets remains limited. This study aimed to characterize trends, demographics, clinical signs, diagnostics, and outcomes in dogs and cats exposed to bromethalin over a 14-year period.

Methods
This retrospective study analyzed 223 cases (123 dogs, 100 cats) submitted to the California Animal Health and Food Safety Laboratory between 2010 and 2023. Desmethylbromethalin (DMB), a toxic bromethalin metabolite, was detected using liquid chromatography–mass spectrometry (LC–MS/MS). Sample types, clinical signs, MRI findings, and autopsy results were reviewed. Statistical comparisons were conducted between species and across time periods.

Results
Submissions rose 2.8-fold from 59 (2010–2016) to 164 (2017–2023). Cats were significantly younger than dogs (median 24 vs. 36 months) and more likely to test positive for DMB (43% vs. 14%; p < 0.0001). Adipose tissue was the most sensitive diagnostic sample. Clinical signs varied: dogs often exhibited seizures and altered mentation, consistent with a “convulsant syndrome,” while cats more frequently showed ataxia and paresis, aligning with a “paralytic syndrome.” MRI findings in 13 of 17 cases (77%) showed changes consistent with bromethalin-induced leukoencephalopathy. Autopsies confirmed CNS white matter damage in most cats but less consistently in dogs. Notably, bromethalin was also detected in milk in one case, raising concerns for lactational transmission.

Limitations
Retrospective design and incomplete clinical records limited data uniformity. LC–MS/MS results were qualitative, precluding dose-response analyses. Many cases lacked complete MRI or histopathology. Cases originated from a single toxicology laboratory, potentially limiting generalizability.

Conclusions
Bromethalin toxicosis in dogs and cats is increasing, with cats more frequently affected and more likely to show diagnostic evidence of exposure. Adipose tissue is the most reliable diagnostic matrix. MRI is emerging as a useful antemortem diagnostic tool. Findings underscore the need for greater awareness of bromethalin risk, especially in young or outdoor-access animals, and highlight possible lactational transmission.

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