CriticalMacrolide antibiotic×Atypical antipsychotics
Updated · Methodology
Mechanism
Clarithromycin blocks CYP3A4 – the main quetiapine metabolic route. Quetiapine plasma levels rise 6-fold, with stronger sedation, orthostatic hypotension, and QT effect.
Symptoms
Marked sedation, drowsiness, orthostatic hypotension with syncope on standing. Tachycardia, QT prolongation. In older patients: fall and fracture risk.
Management
The AEMPS label for quetiapine lists the combination with CYP3A4 inhibitors, clarithromycin included, as contraindicated. The FDA label reduces the quetiapine dose sixfold with ECG monitoring instead. Alternative antibiotics: azithromycin or doxycycline, with little effect on CYP3A4. Alternative antipsychotics without CYP3A4 dependence: olanzapine or aripiprazole.
Check the full regimen, not just this pair
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Sources
- FDA: Seroquel (quetiapine fumarate) prescribing information (2013)– ; DailyMed setid 8ae62aaf-f8c5-417f-baac-0098369ca322
- AEMPS: Ficha técnica: Quetiapina (nº registro 72882), sección 4.3 (2024)– AEMPS, CIMA, nº registro 72882, sección 4.3