A Case Report of Phenytoin Intoxication Identified with Capillary Electrophoresis.

A 2-year and 5-month old male child was admitted to our hospital, deu to signs of antiepileptic drug intoxication. He had been administered zonisamide and valproic acid for the treatment of epilepsy. One day after taking the medicines prepared in an outside pharmacy according to the doctor's prescription, he showed ataxia. The serum valproic acid concentration was within the normal therapeutic range, when measured using the fluorescence polarization immunoassay method (FPIA). We assayed the zonisamide concentration in patient serum using the capillary electrophoresis method. The peak of zonisamide was very low, but another extremely high peak was found. This peak was identified as phenytoin based on the migration time and absorption spectrum. We therefore concluded that the patient fell into phenytoin intoxication by taking a large amount of phenytoin that had been incorrectly prepared. The capillary electrophoresis method appears to be useful for therapeutic drug monitoring, especially in drug intoxication, because of its specificity of separation, simultaneous determination, speed of analysis, and small injection volume.