carbamazepine and clarithromycin

Pharmacokinetic interaction: carbamazepine is metabolised by cytochrome P450 3A4. Clarithromycin is a potent inhibitor of CYP3A4. Coadministration reduces the clearance of carbamazepine, leading to markedly increased plasma concentrations.

Carbamazepine toxicity can occur, manifesting as dizziness, ataxia, diplopia, nystagmus, confusion, and in severe cases, respiratory depression, coma, or cardiac arrhythmias. Conversely, carbamazepine induces CYP3A4, which may reduce clarithromycin efficacy, though this is of lesser clinical concern.

Avoid coadministration where possible. If combined therapy is necessary, monitor carbamazepine plasma concentrations at baseline and after initiation of clarithromycin, and adjust the carbamazepine dose accordingly. Monitor the patient for clinical signs of toxicity. Consider alternative antibiotics with less CYP3A4 inhibition, such as azithromycin.

Well-established interaction supported by numerous case reports, clinical pharmacokinetic studies, and manufacturer labelling. The magnitude of carbamazepine elevation is typically two- to three-fold, with clinical toxicity reported in many cases.