Intermittent complete atrioventricular block after long term low-dose carbamazepine therapy with a serum concentration less than the therapeutic level

After twelve months of low dose carbamazepine therapy ( 200 mg daily) for temporal lobe epilepsy, a 66-year-old woman presented to the hospital complaining of frequent episodes of sudden dizziness. Because Holter monitoring documented intermittent complete atrioventricular block, the patient was admitted to the hospital when the serum concentration of carbamazepine was 4 mu g/mL. After discontinuation of carbamazepine, the patient returned to normal sinus rhythm. The present case suggests that complete atrioventricular block may occur long after initiation of carbamazepine therapy in an older woman even if the daily dosage or the serum concentration of carbamazepine is low.