Central Nervous System Depression After Topical Administration of Brimonidine Eye Drops to Induce Vomiting in a Cat

Brimonidine stimulates the chemoreceptor trigger zone via alpha-2 adrenergic receptors in the postrema of the medulla, which triggers vomiting in cats. This case report details the occurrence of central nervous system (CNS) depression following brimonidine administration to induce vomiting in a cat that had ingested a toxic substance. A 12-year-old neutered male American Shorthair cat was presented to the hospital after ingesting two leaves of Anthurium polyschistum, which is toxic to cats. 0.15% of brimonidine eye drops intended for ocular administration were accidentally administered onto the upper eyelids, resulting in the administration of four drops in total. Three incidents of projectile vomiting were then observed 30 min after the brimonidine administration. The cat began to show signs of CNS depression, including deep sedation and respiratory depression after vomiting. Brimonidine use was the suspected aetiology of the CNS depression. Atipamezole (200 µg/kg) was administered intramuscularly; after 5 min, the clinical signs of the CNS depression resolved. This case suggests that while brimonidine may serve as an effective emetic agent in feline patients, its systemic effects, particularly CNS depression, warrant careful monitoring. The potential impact of higher concentrations and increased dosing volume remains uncertain, highlighting the need for further research to establish safe and standardized dosing guidelines.