Lack of Pharmacokinetic Interaction of Carbamazepine With Tranylcypromine

To the Editor.—  Carbamazepine, a tricyclic compound routinely used in the treatment of epilepsy and trigeminal neuralgia, is also effective in the short-term and prophylactic treatment of bipolar affective disorder.¹ As the clinical use of carbamazepine increases, it is likely that it will be used in combination with a variety of psychotropic agents, including lithium carbonate, other antidepressants, and monoamine oxidase inhibitors. There have been several reports of a marked rise in serum carbamazepine concentrations, with associated toxicity, caused by concomitant administration of isoniazid,^2-4 which is the monoamine oxidase inhibitor used in the treatment of tuberculosis. To our Knowledge, there are no data to indicate whether this interaction with isoniazid is characteristic of monoamine oxidase inhibitors in general and those routinely used in the treatment of depression in particular. Herein, we report a case in which tranylcypromine sulfate was added to existing carbamazepine treatment without the induction of