Carbamazepine-erythromycin interaction. Case studies and clinical significance.

Because of significant and seemingly haphazard fluctuations in serum carbamazepine concentrations, we decided to investigate the possible link between erythromycin administration and potential changes in serum carbamazepine concentration. We studied four cases involving this combination. In every case, serum carbamazepine concentrations either rose dramatically (doubled or tripled previous steady-state concentrations) or dropped precipitously once erythromycin therapy was discontinued. In all cases, we report serum carbamazepine concentrations obtained before, during, and after concurrent erythromycin administration. We conclude that the combination of erythromycin and carbamazepine represents a clinically significant drug interaction and should be avoided where possible.