Can metronidazole (antibiotic) cause heart palpitations (tachycardia)?

Metronidazole and Heart Palpitations

Metronidazole can cause heart palpitations and tachycardia, particularly in susceptible individuals, and should be discontinued if cardiac symptoms develop. 1

Mechanism and Risk

Metronidazole belongs to the nitroimidazole class of antibiotics and, while not commonly listed among the most cardiotoxic medications, can affect cardiac function through several mechanisms:

• Direct cardiac effects: Though less documented than other antibiotics, metronidazole has been associated with cardiac rhythm disturbances in rare cases 2
• Drug interactions: Metronidazole can interact with other medications that affect cardiac conduction, potentially increasing the risk of arrhythmias 1
• Acetaldehyde accumulation: When combined with alcohol, metronidazole can cause accumulation of acetaldehyde, which is cardiotoxic and arrhythmogenic 3

Evidence for Cardiac Effects

The European Society of Cardiology (ESC) guidelines acknowledge that while certain antibiotics (particularly macrolides, quinolones, and azithromycin) are more commonly associated with cardiac arrhythmias, other antimicrobial agents can also trigger cardiac events 1. Although metronidazole is not specifically highlighted in these guidelines as a major cause of arrhythmias, case reports have documented cardiac effects:

• A case report documented ventricular fibrillation in a young patient following metronidazole overdose with no other precipitating factors 2
• Another report described sudden death due to metronidazole/ethanol interaction, with cardiac dysrhythmia attributed to acetaldehyde toxicity 3

Risk Factors for Metronidazole-Induced Palpitations

Patients at higher risk for experiencing cardiac effects from metronidazole include those with:

• Pre-existing cardiac conditions
• Electrolyte abnormalities
• Concurrent use of other QT-prolonging medications
• Alcohol consumption during treatment
• Low albumin levels and tachycardia (which were associated with poorer outcomes in patients receiving ceftriaxone plus metronidazole) 4

Management Recommendations

If a patient reports palpitations while taking metronidazole:

1. Discontinue the medication if clinically appropriate 1
2. Perform a cardiac evaluation including ECG to assess for QT prolongation or other arrhythmias
3. Check for drug interactions with other medications the patient may be taking
4. Ensure the patient avoids alcohol during and for at least 48 hours after completing metronidazole therapy
5. Consider alternative antibiotics based on the indication and sensitivity patterns

Important Considerations

• Alcohol interaction: Patients must be warned about the disulfiram-like reaction that can occur when consuming alcohol while taking metronidazole, which can lead to cardiac complications 3
• Monitoring: Patients with pre-existing cardiac conditions should be monitored more closely when prescribed metronidazole
• Duration of therapy: The risk of adverse effects, including cardiac effects, may increase with prolonged therapy 5

While metronidazole is generally well-tolerated with primarily mild to moderate gastrointestinal side effects, clinicians should remain vigilant about potential cardiac manifestations, especially in high-risk patients or those reporting new-onset palpitations during treatment.