The influence of antiepileptic drugs on the electroencephalogram: a review of controlled clinical studies.

The effect of antiepileptic drugs on the EEG was studied in a review of 23 controlled trials with therapeutic drug monitoring and serial EEG observations. There is a good correlation of suppression of paroxysmal discharges and an increase in the plasma concentrations of diazepam, phenobarbital, phenytoin, alone or in combination with phenobarbital or primidone. The correlation is variable during treatment with carbamazepine and in patients with focal discharge receiving sodium valproate or a delayed response to sodium valproate treatment. An increase in beta activity is correlated with a raised plasma concentration of clonazepam, phenytoin and phenobarbital, but not in all patients receiving these drugs. The degree and the localization of cerebral impairment seem to influence the drug-induced fast EEG response. Slowing of background occurs with high plasma concentrations of diazepam, phenytoin, alone or in combination with phenobarbital or primidone. The correlation of paroxysmal discharges with clinical seizure frequency is good for phenobarbital, phenytoin, alone or in combination. The correlation is variable for carbamazepine and the delayed response to sodium valproate. A slowing of background activity is correlated with clinical drug toxicity due to carbamazepine, phenytoin, phenobarbital and primidone treatment in most patients.