What is the interaction between Seroquel (quetiapine) and Flecainide?

Interaction Between Quetiapine (Seroquel) and Flecainide

Concurrent use of quetiapine (Seroquel) and flecainide carries a significant risk of QT prolongation and potentially life-threatening cardiac arrhythmias, and should be avoided whenever possible.

Mechanism of Interaction

• Both medications can independently affect cardiac conduction and repolarization, creating a potentially dangerous additive effect 1:

  • Flecainide is a class IC antiarrhythmic that blocks sodium channels, affecting cardiac conduction primarily by prolonging the QRS interval 2, 3
  • Quetiapine can also affect cardiac repolarization, and when combined with flecainide, can trigger or unmask Brugada ECG patterns and increase arrhythmia risk 1

• The combination may lead to:

  • QT interval prolongation 4, 5
  • Increased risk of torsades de pointes 4
  • Potential for Brugada pattern on ECG 1

Clinical Significance

• Case reports document serious cardiac events when these medications are used together, including:

  • Cardiac arrest due to polymorphic ventricular tachycardia 6
  • Brugada ECG pattern emergence 1
  • QT prolongation leading to life-threatening arrhythmias 4

• Flecainide has been associated with increased mortality in patients with structural heart disease 2, and this risk may be compounded by concurrent quetiapine use

Monitoring Recommendations

• If concurrent use cannot be avoided:

  • Obtain baseline ECG prior to initiating either medication 3
  • Monitor QRS duration regularly - an increase >25% from baseline indicates potential proarrhythmia risk requiring dose reduction or discontinuation 3
  • Watch for QT prolongation on ECG 6, 4
  • Monitor for symptoms of arrhythmia (syncope, palpitations, dizziness) 6

• Special attention should be paid to:

  • Electrolyte imbalances (especially potassium, magnesium) 4
  • Other QT-prolonging medications in the regimen 2
  • Underlying cardiac conditions that increase risk 3

Risk Factors for Adverse Outcomes

• Patients at highest risk for adverse outcomes include those with:
  • Structural heart disease or coronary artery disease 2
  • History of myocardial infarction 2
  • Reduced left ventricular ejection fraction 3
  • Electrolyte abnormalities 4
  • Concomitant use of other medications affecting cardiac conduction 2, 1

Management Recommendations

• Whenever possible, avoid concurrent use of quetiapine and flecainide 1

• Consider alternative antipsychotic medications with lower risk of QT prolongation if flecainide is required 7

• If flecainide is needed in a patient on quetiapine, consider alternative antiarrhythmic options based on the specific indication:

  • For atrial fibrillation: amiodarone may be safer in patients with structural heart disease 2
  • For supraventricular tachycardia: consider catheter ablation rather than medication therapy 2

• If concurrent use is unavoidable:

  • Use the lowest effective doses of both medications 6
  • Implement strict ECG monitoring schedule 3
  • Consider cardiology consultation for specialized management 3
  • Educate patients about warning signs requiring immediate medical attention (syncope, palpitations) 6

Common Pitfalls

• Failing to recognize the additive effects on cardiac conduction when these medications are combined 1
• Overlooking the need for more frequent ECG monitoring when both drugs are used 3, 6
• Not considering drug interactions when investigating unexplained syncope or arrhythmias 6
• Neglecting to adjust dosing when initiating or discontinuing either medication 3