Can metronidazole 500 mg and clarithromycin 500 mg cause dizziness or syncope?

Can Metronidazole 500mg and Clarithromycin 500mg Cause Dizziness or Syncope?

Yes, both metronidazole 500mg and clarithromycin 500mg can cause dizziness, and both have been associated with syncope, though through different mechanisms and with varying frequency.

Metronidazole-Related Dizziness and Neurological Effects

Metronidazole commonly causes dizziness as a direct adverse effect, and in rare cases can cause severe neurological toxicity including cerebellar dysfunction and ataxia. 1, 2

• Dizziness is listed among the generic side-effects of metronidazole, along with nausea, vomiting, and metallic taste 3
• Metronidazole-induced encephalopathy is a rare but serious complication that presents with progressive vertigo, ataxia, and cerebellar dysfunction, particularly with prolonged use (typically >2 weeks) 1
• The characteristic presentation includes dysarthria, downbeat nystagmus, gait ataxia, and tingling sensations 2
• MRI findings in metronidazole neurotoxicity show T2 and FLAIR hyperintensities in dentate nuclei and splenium of the corpus callosum 2
• Syncope has been reported as a rare side-effect of metronidazole 3
• Symptoms typically improve rapidly after discontinuation of metronidazole, though peripheral neuropathy symptoms (lower limb paresthesias) may persist 2

Clarithromycin-Related Cardiovascular and Neurological Effects

Clarithromycin can cause dizziness, vertigo, and confusion, and has been associated with QT prolongation and cardiac arrhythmias that may lead to syncope. 4, 5

• The FDA drug label explicitly warns about the potential for dizziness, vertigo, confusion, and disorientation with clarithromycin 5
• Clarithromycin prolongs the QT interval and can cause cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsades de pointes 4
• Clarithromycin should not be given to patients with history of QT prolongation or ventricular cardiac arrhythmia 4
• The cardiovascular risks are particularly concerning when clarithromycin is combined with other QT-prolonging medications 4
• Decreased hearing has been reported with clarithromycin use, which may contribute to balance disturbances 4

Clinical Monitoring Recommendations

When prescribing these medications together, monitor for both neurological symptoms (from metronidazole) and cardiovascular symptoms (from clarithromycin).

• For metronidazole: Watch for progressive dizziness, ataxia, tingling, or gait disturbances, especially if treatment extends beyond 2-3 weeks 1, 2
• For clarithromycin: Obtain baseline ECG in high-risk patients (elderly, female, pre-existing cardiac disease, concomitant QT-prolonging drugs) 4
• Correct electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, before starting clarithromycin 4
• Discontinue clarithromycin immediately if QTc exceeds 500 ms or increases >60 ms from baseline 4

Common Pitfalls to Avoid

• Do not dismiss new-onset dizziness or ataxia in patients on metronidazole as benign—metronidazole-induced encephalopathy can lead to permanent sequelae if not recognized and treated promptly 1
• Do not combine clarithromycin with other QT-prolonging medications without careful risk assessment and ECG monitoring 4
• Do not continue metronidazole if cerebellar symptoms develop—immediate discontinuation is required 1, 2
• Metronidazole neurotoxicity is often underrecognized in clinical practice, particularly in elderly patients on prolonged treatment 2

Drug Interaction Considerations

• Clarithromycin is a potent CYP3A4 inhibitor and can increase levels of other medications metabolized by this pathway 4
• The combination of clarithromycin with digoxin requires dose reduction of digoxin by 30-50% and monitoring of digoxin levels 4
• Clarithromycin should not be used concomitantly with certain medications including astemizole, cisapride, pimozide, terfenadine, ergotamine, or dihydroergotamine due to risk of serious cardiac arrhythmias 4