Possible carbamazepine toxicity with terbinafine.

OBJECTIVE To report a case of carbamazepine and terbinafine interaction resulting in an elevated level of carbamazepine and associated symptoms of toxicity. CASE SUMMARY A 50-year-old Caucasian man developed an elevated carbamazapine level after starting terbinafine, which caused symptoms of toxicity with gait ataxia, dizziness and falls. DISCUSSION This is a first report of a drug-drug interaction between carbamazapine and terbinafine. Although the mechanism for this interaction is not fully known, it is suspected that terbinafine decreased the metabolism of carbamazapine and led to increased levels that continued even days after the carbamazapine had been stopped. The Naranjo Scale suggests that this was a probable interaction (score 6). CONCLUSIONS While several drug-drug interactions have been reported with carbamazapine, there are no previous reports of its interaction with terbinafine. Prescribers should exercise caution when prescribing these medications together.