What happens if a patient takes an extra dose of flecainide (antiarrhythmic medication)?

Management of Flecainide Overdose

An extra dose of flecainide can lead to life-threatening cardiac toxicity requiring immediate medical attention, especially in patients with underlying cardiac conditions. 1

Clinical Manifestations of Flecainide Overdose

Flecainide overdose can present with a spectrum of cardiac abnormalities:

• Electrocardiographic changes:

  • QRS complex widening (>25% from baseline)
  • PR interval prolongation (>0.3 seconds)
  • QT interval prolongation
  • Development of new bundle branch block

• Cardiac rhythm disturbances:

  • Ventricular tachyarrhythmias
  • Bradycardia
  • Atrial flutter with 1:1 AV conduction
  • AV nodal block
  • Asystole
  • Bundle branch block

• Other symptoms:

  • Hypotension
  • Syncope
  • Convulsions
  • Nausea and vomiting
  • Dizziness
  • Visual disturbances
  • Cardiac arrest in severe cases

Management Algorithm

1. Immediate Assessment and Stabilization

• Assess vital signs and cardiac monitoring
• Obtain 12-lead ECG to evaluate QRS duration, PR interval, and rhythm
• Establish IV access
• Obtain baseline laboratory studies including electrolytes and renal function
• Determine amount of extra dose taken and timing

2. Treatment Based on Severity

For Mild Overdose (minimal ECG changes, stable hemodynamics):

• Close monitoring for at least 24 hours due to long half-life (12-27 hours) 1
• Consider holding next scheduled dose
• Monitor for development of symptoms or ECG changes

For Moderate to Severe Overdose:

First-line treatment:

• Sodium bicarbonate therapy: Initial bolus of 1-2 mEq/kg IV (or 50-100 mL of 8.4% solution) followed by continuous infusion 2, 3
  • Goal: Narrow QRS complex and improve conduction
  • Monitor serum pH and electrolytes

Additional interventions as needed:

• Calcium gluconate (1-2 g IV) to stabilize myocardial cell membranes 2, 4
• Inotropic agents or cardiac stimulants (dopamine, dobutamine, isoproterenol) for hemodynamic support 1
• Mechanically assisted ventilation if respiratory compromise occurs 1
• Circulatory assist devices such as intra-aortic balloon pumping in severe cases 1
• Transvenous pacing for significant conduction block 1
• For refractory cases: Consider intravenous lipid emulsion therapy or extracorporeal membrane oxygenation (ECMO) 5

3. Important Considerations

• Duration of treatment: Extended supportive care may be necessary due to flecainide's long half-life 1
• Hemodialysis: Not effective for removing flecainide from the body 1
• Urine acidification: Theoretically may promote drug excretion in cases with alkaline urine, but limited evidence supports this approach 1
• Risk factors for increased toxicity:
  • Renal impairment (CrCl ≤35 mL/min)
  • Hepatic dysfunction
  • Heart failure
  • Concomitant amiodarone therapy
  • Electrolyte disturbances
  • Female gender 2

Prevention of Future Overdose

• Patient education regarding proper dosing schedule and importance of medication adherence
• Consider dose reduction in high-risk patients (renal impairment, elderly)
• For patients using "pill-in-pocket" approach, reinforce clear instructions about maximum dosing and frequency 4
• Regular ECG monitoring and plasma level checks in patients on chronic therapy

Caution

Death has been reported following ingestion of as little as 1000 mg of flecainide 1. Even a single extra dose can cause significant toxicity in patients with risk factors. Flecainide is contraindicated in patients with structural heart disease, coronary artery disease, or significant conduction abnormalities 6, 2.