Doxycycline and QT Prolongation
Doxycycline is not known to cause QT interval prolongation and is considered a safer antibiotic choice for patients with risk factors for QT prolongation. 1
Evidence on Doxycycline and QTc
- Doxycycline is not listed among antibiotics known to cause QT interval prolongation in major cardiac guidelines and consensus documents, making it a preferred choice in patients with risk factors for QT prolongation 1
- Unlike macrolides and fluoroquinolones, doxycycline does not block the human ether-a-go-go-related gene (HERG) potassium channels that are responsible for QT prolongation 1
- In a 2024 study comparing azithromycin and doxycycline in ICU patients, no statistically significant difference was found in QTc interval change with doxycycline use 2
Antibiotics Known to Cause QT Prolongation
- Macrolide antibiotics (azithromycin, clarithromycin, erythromycin) are known to cause QT prolongation and are listed in the European Society of Cardiology guidelines as medications associated with cardiac arrhythmias 3, 1
- Fluoroquinolones, particularly moxifloxacin, carry significant risk of QT prolongation by blocking voltage-gated potassium channels 4
- Trimethoprim is specifically mentioned in European Heart Journal guidelines as an antibiotic that may induce QT interval prolongation 3
Mechanism of QT Prolongation
- QT prolongation typically occurs when drugs block IKr (one of the ionic currents involved in ventricular repolarization) 3, 5
- Many antibiotics that prolong QT interval (macrolides, fluoroquinolones) do so by blocking KNCH2-hERG-K+ channels affecting IKr 5
- Doxycycline has not been demonstrated to have this effect on cardiac ion channels 1
Risk Factors for QT Prolongation
- Electrolyte disturbances (hypocalcemia, hypokalemia, hypomagnesemia) can potentiate drug-induced QT prolongation 3
- Concomitant use of multiple QT-prolonging medications significantly increases risk of torsades de pointes 6, 5
- Pre-existing cardiac conditions, female sex, advanced age, and genetic predisposition are additional risk factors 5
Clinical Implications
- For patients requiring antibiotics who have a history of QT prolongation or are on other QT-prolonging medications, doxycycline would be a safer choice than macrolides or fluoroquinolones 1
- If using antibiotics known to prolong QT interval, monitor cardiac rhythm and QT interval, and consider discontinuing if QTc exceeds 500 ms 1, 6
- The European Society of Cardiology recommends discontinuing QT-prolonging medications if QTc exceeds 500 ms or increases >60 ms from baseline 1
Monitoring Recommendations
- Baseline ECG is recommended before starting known QT-prolonging antibiotics, but this is not necessary when using doxycycline 1, 6
- Maintain serum potassium between 4.5 and 5 mEq/L to reduce the risk of QT prolongation when using QT-prolonging antibiotics 1
- When using QT-prolonging antibiotics (not doxycycline), ECG monitoring should be performed at baseline, once steady-state levels are achieved, with dose adjustments, and with initiation of new medications that may prolong QT interval 1