Can Lasix (furosemide) prolong the QTc interval?

Furosemide and QT Interval Prolongation

Yes, furosemide (Lasix) can prolong the QTc interval, particularly in patients with electrolyte disturbances like hypokalemia and hypomagnesemia. 1

Mechanism and Risk Factors

• Furosemide has been associated with QTc interval prolongation, with studies showing an average increase of approximately 3 milliseconds in the QTc interval 2
• The QT-prolonging effect of furosemide is mediated through two primary mechanisms:
  • Direct effect on cardiac repolarization 1
  • Indirect effect through electrolyte disturbances, particularly hypokalemia and hypomagnesemia, which are common side effects of loop diuretics 3, 4
• Risk factors that increase the likelihood of furosemide-induced QTc prolongation include:
  • Pre-existing cardiac disease 1
  • Advanced age (>65 years) 3
  • Congestive heart failure 3
  • Severe illness 3
  • Elevated C-reactive protein levels 3

Clinical Significance

• QTc prolongation increases the risk of developing torsades de pointes, a potentially fatal ventricular arrhythmia 5
• In a study of COVID-19 patients, those with hypokalemia who received furosemide were five times more likely to develop QTc prolongation compared to those without hypokalemia 3
• Animal studies have demonstrated that furosemide-induced hypokalemia significantly prolongs the QT interval, confirming the relationship between furosemide, electrolyte disturbances, and QT prolongation 4, 6

Monitoring and Management Recommendations

• Obtain a baseline ECG before starting high-dose furosemide therapy, particularly in high-risk patients 1
• Monitor serum potassium and magnesium levels regularly during treatment with furosemide 1
• Maintain serum potassium and magnesium within normal ranges during furosemide therapy 1
• Consider dose reduction or discontinuation of furosemide if the QTc interval reaches >500 ms or increases by >60 ms from baseline 1
• Use caution when combining furosemide with other medications known to prolong the QT interval, such as:
  • Antiarrhythmics (amiodarone, sotalol, procainamide, disopyramide, quinidine) 7
  • Antiemetics (domperidone, metoclopramide, 5HT3 antagonists) 7
  • Antidepressants (particularly tricyclics) 7
  • Antipsychotics 7
  • Antimalarials (chloroquine, hydroxychloroquine) 7
  • Macrolide antibiotics 7

Prevention of QTc Prolongation

• Potassium supplementation has been shown to reduce QTc interval in patients with furosemide-induced QTc prolongation 4
• Consider using potassium-sparing diuretics (e.g., spironolactone) in combination with furosemide in patients at high risk for QTc prolongation, as spironolactone has been associated with QTc shortening 2
• In patients requiring diuresis who are at high risk for arrhythmias, consider alternative diuretics with less impact on QTc interval 1

Special Considerations

• Patients with chronic kidney disease are at particularly high risk for medication-induced QTc prolongation, including from furosemide 2
• The combination of furosemide with other QT-prolonging medications substantially increases the risk of significant QTc prolongation and potential arrhythmias 7, 1
• Even low doses of furosemide may contribute to QTc prolongation in susceptible individuals, especially when combined with other risk factors 2