Phenytoin (PHT) is used commonly in patients with partial and generalized tonic-clonic seizures but is not effective for absence seizures.40

Dose-related sedation may occur, or a paradoxical excited delirium may be seen with either therapeutic or toxic PHT levels.42

PHT's mild effects on cognition are well known. Some studies have demonstrated PHT- induced memory impairments, and others have shown impairments in complex reaction time or motor speed.43,44

Variable reports cite a relationship between PHT and depressive symptoms. Some of this relationship may involve reactive symptoms from experiencing the stigma associated with cosmetic side effects of the drug.41

An older literature describes a chronic cumulative encephalopathy that has an impact on both behavior and global cognition4 and an acute reversible encephalopathy (manifested by increased seizures, drowsiness, and cognitive impairment, sometimes with ataxia) accompanying toxic PHT levels.42 These encephalopathic syndromes should be considered in evaluating developmentally disabled patients who have shown declines in cognition or coordination. Switching of AEDs should be considered if this potentially reversible syndrome is suspected.

Adapted from: Ettinger AB, Barr WB, and Solomon SP. Psychotropic properties of antiepileptic drugs in patients with developmental disabilities. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;219–230. With permission from Elsevier (

Authored By: 
Sanford P. Solomon MD
William B. Barr MD
Alan B. Ettinger MD
Reviewed By: 
Steven C. Schachter MD
Thursday, April 1, 2004