A 5-month-old Labrador presented with seizures and tremors after ingesting a potentially lethal dose of lamotrigine. With symptomatic treatment and vigilant nursing care, he was discharged after 72 hours.

Introduction

Lamotrigine is a member of the sodium channel blocking class of antiepileptic drugs. Lamotrigine in dogs is extensively metabolized to a 2-N-methyl cardiotoxic metabolite, causing a delay in intraventricular conduction and prevents depolarization. Specifically causing dose-dependent prolongation of P-R intervals, widening of QRS complexes and atrioventricular conduction block. ASPCA reports an LD50 of 245 mg/kg, with clinical signs beginning 4 hours post ingestion. This will be the first case report utilizing symptomatic treatment, resulting in a positive outcome, following a lethal dose of 513 mg/kg ingestion.

Synopsis

5-month-old Labrador presented with seizures, tremors, stuporous mentation. On presentation, the owners reported no known toxin ingestion. Intravenous methocarbamol 50 mg/kg, phenobarbital 5 mg/kg and midazolam 0.5 mg/kg were administered with minimal response, followed by continuous infusions of 0.1 mg/kg/min propofol and 0.5 mg/kg/hr midazolam. The owner later reported lamotrigine ingestion as the causative agent.

Following initial therapy, tremors subsided and unifocal ventricular premature complexes (VPCs) with sinus tachycardia developed. The patient then received 2 mg/kg lidocaine followed by a continuous infusion of 25 mcg/kg/min. After 15 hours with unremarkable electrocardiogram changes and significant clinical improvement, the lidocaine was discontinued. Within 48 hours a junctional rhythm with wide QRS complexes and split VPCs were observed. After cardiologist consultation, lidocaine was restarted at 75 mcg/kg/min. Subsequently, a seizure occurred. Lidocaine was decreased to 25 mcg/kg/min. Within 72 hours post ingestion the electrocardiogram abnormalities resolved and the patient was discharged on sotalol at 1.5 mg/kg twice daily. Follow up with a cardiologist was recommended.

Conclusion

While simple treatment was successful, additional interventions to consider for future cases include use of intralipids and placement of a urinary catheter to assist in excretion of the metabolite. This case demonstrated that a positive outcome can be seen at doses greater than 500 mg/kg. It is important to note that without diligent nursing care this outcome could not be achieved.

Disclosures

No disclosures to report.