Effects of high-dose antiepileptic drugs on event-related potentials in epileptic children

N200 and P300 of event-related potentials (ERPs) were recorded from 22 epileptic children receiving high-dose antiepileptic drugs. The patients were undergoing monotherapy with supratherapeutic serum level and were not mentally retarded. P300 latency was prolonged in 5 of 8 patients (62.5%) of the carbamazepine (CBZ) group and in 4 of 7 patients (57.1%) of the phenytoin (PHT) group. Only one child of the PHT group showed abnormality in brain-stem auditory evoked potentials (BAEPs). Abnormality of P300 was more frequent than that of BAEP. In patients of the PHT group who underwent examinations consecutively before and after changing the dose, P300 latency was prolonged rapidly when the PHT level exceeded 30 mu g/ml. This suggested that the prolongation was dose dependent. In all patients of the valproic acid (VPA) group, P300 latency was normal. Only 2 patients of the PHT group had P300 prolongation simultaneously with clinical signs of intoxication. Others demonstrated changes in P300 without symptoms of side effects.