Major
Carbamazepine × Clarithromycin
Antiepileptics. Carboxamide derivatives×Macrolide antibiotic
Mechanism
Clarithromycin inhibits CYP3A4, the carbamazepine metabolism enzyme. Carbamazepine concentration doubles, causing toxicity: ataxia, diplopia, hyponatraemia. Effect differs from other macrolides: azithromycin does not inhibit CYP3A4.
Symptoms
Within 3–5 days: dizziness, unsteady gait, diplopia, nausea. In the elderly – confusion, sodium below 130 mmol/L.
Management
For infection in a carbamazepine patient, choose azithromycin or another class (amoxicillin for typical pneumonia). If clarithromycin is required, cut carbamazepine by 30% and check level after 3 days.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.