What are the signs and symptoms of a Lamictal (lamotrigine) overdose?

Signs and Symptoms of Lamotrigine Overdose

Lamotrigine overdose can cause life-threatening symptoms including seizures, cardiac conduction abnormalities, and altered mental status that may progress to coma, respiratory arrest, and death.

Clinical Manifestations

Neurological Symptoms

• Seizures - Present in up to 55% of overdose cases 1
  • Can occur as early as 20-60 minutes after ingestion 2
  • Children appear more susceptible, with seizures reported at lower serum concentrations (3.8 mg/L vs 25.6 mg/L in adults) 1
• Altered mental status
  • Ranges from drowsiness to coma requiring ventilatory support 3
  • Glasgow Coma Scale ≤8 in 20% of cases 1
• Ataxia 4
• Nystagmus 2
• Hyperreflexia 2
• Alternating periods of drowsiness and irritability 2

Cardiovascular Symptoms

• Cardiac conduction abnormalities
  • QRS interval prolongation 5
  • Complete heart block 5
• Wide complex tachycardia (6% of cases) 1
• Hypotension (12% of cases) 1
• Cardiac arrest (6% of cases) 1
  • Primarily in adult patients with serum concentrations >25 mg/L 1

Other Symptoms

• Gastrointestinal effects
  • Nausea and vomiting 4
• Respiratory depression
  • May progress to respiratory arrest 5
• Rhabdomyolysis 3
• Multi-organ failure in severe cases 5

Risk Factors and Severity Indicators

Dose-Related Considerations

• Adults: Severe toxicity may occur with serum concentrations >25 mg/L 1
• Children: Ingestions ≥525 mg may produce severe CNS depression and seizures 1
  • Children ≤3.5 years appear particularly vulnerable 1
  • Toxicity has been reported with doses as low as 25 mg/kg/day 4

High-Risk Populations

• Young children without underlying seizure disorders appear more susceptible to CNS toxicity 1
• Co-ingestion with other substances (particularly ethanol) may worsen clinical presentation 3

Management Considerations

While not directly addressing lamotrigine overdose, general principles for management of toxic ingestions include:

1. Airway management and ventilatory support are critical priorities in patients with respiratory depression 6
2. Seizure control with benzodiazepines 1
3. Cardiac monitoring for conduction abnormalities 1
4. Supportive care including fluid resuscitation 1

Clinical Pitfalls and Caveats

• Rapid progression: Seizures can occur within 20-60 minutes of ingestion 2
• Deceptive presentation: Initial symptoms may be mild but can rapidly progress to life-threatening toxicity 1
• Gastrointestinal decontamination may be contraindicated due to seizure risk 2
• Pediatric sensitivity: Children may experience toxicity at lower doses and serum concentrations than adults 1
• Delayed effects: Patients should be observed for at least 12 hours after ingestion 2

In any suspected lamotrigine overdose, prompt medical attention is essential as symptoms can rapidly progress from mild to life-threatening, particularly in pediatric patients and those with large ingestions.