Diphenylhydantoin serum levels, toxicity, and neuropsychological performance in patients with epilepsy.

The neuropsychological effects of diphenylhydantoin were assessed in 70 adults having primarily psychomotor and major motor seizures. All patients were stabilized on diphenylhydantoin alone, and assessment of this drug by gas-liquid chromatography provided a basis for dichotomizing the group into High and Low drug groups, both with and without toxic patients. In addition, patients showing signs of toxicity were contrasted with those not showing such signs. In each of these comparisons, control was maintained with respect to the variables of age, education, age at onset of disorder, and duration of disorder. Neuropsychological assessment was by means of the test battery originated by Halstead and developed by Reitan. Results showed that the High and Toxic Groups rather consistently did more poorly on all tasks than the Low and Nontoxic Groups. However, differences which were statistically significant appeared only in connection with tasks which had a heavy motor component. Possible reasons for the lack of statistically significant differences on the higher level mental tasks were presented.