Carbamazepine toxicity induced by clarithromycin coadministration in psychiatric patients

Seven psychiatric inpatients receiving carbamazepine 600 mg/day were coadministered clarithromycin 400 mg/day for 5 days to treat atypical pneumonia. Blood samples were taken after clarithromycin coadministration and at 1 and 4 weeks after its discontinuation. Plasma concentrations of carbamazepine and carbamazepine-10,11-epoxide were measured using high-performance liquid chromatography. During clarithromycin coadministration, four out of the seven patients developed moderate-to-severe toxic symptoms of carbamazepine, such as drowsiness, dizziness, and ataxia, which resolved within 5 days after clarithromycin discontinuation. In these four patients, plasma carbamazepine concentrations after clarithromycin coadministration were approximately twice as high as those after its discontinuation. In the seven patients, the mean plasma concentration of carbamazepine, but not of carbamazepine-10,11-epoxide, after clarithromycin coadministration was significantly (p < 0.01) higher than those at 1 and 4 weeks after its discontinuation. The present report suggests that clarithromycin coadministration induces increased plasma carbamazepine concentrations, which may result in carbamazepine toxicity. Therefore, care should be given to prescribing clarithromycin for patients receiving carbamazepine.