What medications can prolong the QTc (QT interval corrected) interval on an electrocardiogram (ECG)?

Medications That Can Prolong the QTc Interval on ECG

Multiple medication classes can prolong the QTc interval on ECG, including antiarrhythmics, antipsychotics, antibiotics, and other drugs that affect cardiac repolarization. 1

Antiarrhythmic Medications

• Class IA antiarrhythmics: quinidine, procainamide, disopyramide 1
• Class III antiarrhythmics: amiodarone, sotalol, dofetilide, ibutilide 1
  • Sotalol can cause QT prolongation and torsades de pointes, requiring close monitoring during initiation and dose adjustments 2
  • Dofetilide is associated with significant QT prolongation and requires hospitalization during initiation 1
  • Amiodarone causes marked QT prolongation but has a relatively lower risk of torsades de pointes compared to other antiarrhythmics 1

Antipsychotic Medications

• First-generation (typical) antipsychotics have higher risk of QT prolongation 3, 4:
  • Chlorpromazine, haloperidol (especially IV), thioridazine 3, 5
• Second-generation (atypical) antipsychotics with QT prolongation risk 6, 5, 7:
  • Ziprasidone (highest risk among SGAs) 7
  • Quetiapine (moderate risk) 6
  • Olanzapine (moderate risk) 7
  • Amisulpride (moderate risk) 7
  • Aripiprazole and lurasidone (minimal risk) 5

Antimicrobial Agents

• Macrolide antibiotics: azithromycin, clarithromycin, erythromycin 1, 8
  • Clarithromycin has been associated with prolongation of the QT interval and cases of torsades de pointes 8
• Fluoroquinolones: moxifloxacin, gatifloxacin 6, 9
• Antifungals: ketoconazole, voriconazole, itraconazole, fluconazole 1
• Antimalarials: chloroquine, hydroxychloroquine 1
• Antitubercular drugs: bedaquiline 1

Other Medications

• Antiemetics: domperidone, metoclopramide, 5HT3 antagonists (ondansetron) 1, 9
• Antidepressants: tricyclic antidepressants 1, 4
• Calcium channel blockers: verapamil, diltiazem 8, 9

Risk Factors for QT Prolongation and Torsades de Pointes

• Patient-specific factors 1:

  • Female sex
  • Older age
  • Heart disease (especially LV hypertrophy, ischemia, or low ejection fraction)
  • Bradycardia
  • Electrolyte abnormalities (hypokalemia, hypomagnesemia)
  • Genetic predisposition to QT prolongation
  • Concomitant use of multiple QT-prolonging medications

• ECG warning signs 1:

  • QTc >500 ms
  • Increase in QTc >60 ms from baseline
  • T wave abnormalities
  • Bradycardia or long pauses
  • Polymorphic ventricular premature beats

Monitoring Recommendations

• Baseline ECG before starting QT-prolonging medications 1
• Follow-up ECG monitoring 1:
  • For high-risk drugs (dofetilide, sotalol): continuous monitoring during initiation
  • For moderate-risk drugs: ECG at 3-6 months and when adding other QT-prolonging drugs
• Electrolyte monitoring (potassium, magnesium) at baseline and periodically 1
• Renal function assessment for medications eliminated renally (dofetilide, sotalol) 1

Management of QT Prolongation

• Discontinue the offending drug if QTc >500 ms or increases >60 ms from baseline 1
• Correct electrolyte abnormalities (potassium, magnesium) 1
• Avoid combinations of multiple QT-prolonging drugs 6, 8
• Consider alternative medications with lower risk of QT prolongation 5, 4
• Continuous ECG monitoring until QTc returns to baseline after discontinuing the offending drug 1

Common Pitfalls and Caveats

• Underestimating additive effects of multiple QT-prolonging medications 1, 8
• Failing to recognize non-cardiac medications that prolong QT 9, 4
• Inadequate monitoring of electrolytes in patients on diuretics and QT-prolonging drugs 1
• Not accounting for drug interactions that can increase levels of QT-prolonging medications 8
• Overlooking patient-specific risk factors that predispose to QT prolongation 1, 5