A previous report from the University of Washington School of Medicine, Seattle, WA that carbamazepine had fewer adverse neuropsychological effects than phenytoin has been re-evaluated. When patients with disproportionately high phenytoin levels were excluded, the neuropsychological differences originally reported could not be demonstrated by statistical analysis. [1]

COMMENT. Two additional studies have found no definite adverse cognitive effects that could be related to phenytoin [2, 3]. The authors comment that many studies reporting adverse cognitive effects of phenytoin use computerized tests heavily loaded with motor speed. When the motor speed element is factored out, the cognitive effects also disappear.

Cognitive function in relation to time-of-day variation in serum carbamazepine concentration in epileptic patients is reported from the Neuropsychology Laboratory, Department of Psychosomatic and Behavioral Medicine, Rikshospitalet, Oslo, Norway [4]. Patients had been seizure-free for at least one month and took 2 daily CBZ doses. The test battery showed no differences between performance at times of high versus low serum concentrations. A 33% fluctuation in CBZ concentrations during the day was significant. The subjects were mainly adults and different results might be obtained in children.