Severe lamotrigine toxicosis in a dog

OBJECTIVE: The objective of this study was to describe a case of severe lamotrigine toxicosis in a dog, which was successfully treated using minimal medical interventions. CASE SUMMARY: A 7-month-old male, intact, Labrador mix was evaluated because of acute onset of vomiting, rigidity, and dull mentation after ingesting lamotrigine tablets. The estimated oral dose that had been ingested was 278 mg/kg (611.6 mg/lb). Physical examination was unremarkable other than abnormalities noted in the cardiovascular and neurological systems. Neurological examination revealed dull mentation, vertical nystagmus, four-legged extensor limb rigidity, and alligator rolling. Cardiovascular examination revealed pale pink mucous membranes and multifocal ventricular tachycardia. Intravenous (IV) fluids were started at three times maintenance (180 mL/kg/day). Methocarbamol (100 mg/kg [220 mg/lb], rectally) and lidocaine (2 mg/kg [4.4 mg/lb, IV]) were administered. Twenty-four and seventy-two hours after presentation, the dog was clinically normal with no ventricular tachycardia being noted. CONCLUSION: Lamotrigine (6-[2,3-dichlorophenyl]-1,2,4-triazine-3,5-diamine) is an anticonvulsant medication used in humans, which inhibits voltage-gated sodium channels. The clinical success of this case suggests that administration of only methocarbamol for the neurologic effects and lidocaine for the arrhythmias, as well as supportive IV fluid therapy, could be a successful treatment strategy for dogs, even with severe lamotrigine toxicosis.