Phenytoin-Induced Cardiac Conduction Abnormalities

Phenytoin possesses electrophysiological effects consistent with those of the Vaughan–Williams 1B classification. As such, phenytoin may widen the QRS complex but would not be expected to result in QTc prolongation or ST elevation. The reported case demonstrates these unexpected electrophysiological effects with supratherapeutic concentrations of phenytoin when no other potential cause could be elucidated. No contributing factors present in the case, compared with previously published reports of electrophysiological effects of supratherapeutic phenytoin concentrations, could be elucidated. The report suggests that clinicians should monitor for potential conduction abnormalities in patients with elevated phenytoin concentrations.