[Valproic acid in the treatment of epilepsy with special emphasis on serum level determination (author's transl)].

Valproic acid has become a regular component of antiepileptic therapy. Generally it is used against genetically caused, primary generalized epilepsies with bilateral hypersynchronous neuronal discharges in the EEG. An improvement can also be observed by Valproic acid-treatment for secondary generalized and partial epilepsies. Therapeutic results could possibly be improved through a consideration of the serum concentration of valproic acid. Some of the commercial preparations contain the sodium salt of Valproic acid. The free acid which is quickly absorbed, is released in the stomach (tablet) or in the intestine (dragee). The half life is about 15 to 17 hours (one finds a range of 6 to 20 hours in the literature). In view of the half life, it is recommended that the daily dose should be divided into three single doses. About 84 to 95% of the substance is protein bound. Up to now, clinically relevant observations concerning the displacement of valproic acid from its protein binding are unknown. Recently in in vitro studies a decreased protein binding of valproic acid due to phenylbutazone, salicylic acid, and sulfadimethoxine and vice versa, a displacement of phenobarbital and phenytoin caused by valproic acid could be demonstrated. The therapeutic range of the serum level was between 50 and 120 mcg/ml. Individual patients showed that the dispensed dose did not reliably yield the expected serum levels. The necessary daily dose lies for adults between 600 and 2400 mg, in children between 15 and 150 mg/kg. The wide range of allowable dosis is dependent on whether or not valproic acid is to be given in conjunction with other antiepileptic drugs. When phenobarbital and valproic acid are given in conjunction one should be alert for a rise in the phenobarbital serum level. Results of studies in which valproic acid was combined with several other antiepileptic and psychotropic drugs are reported. The majority of the researchers determine a clear parallelism between clinical improvement and a normalization of the EEG in primary generalized epilepsies with bilateral synchronous 3/sec. spikes and waves. The background activity, determined by visual inspection, is not affected. Few workers discuss the correlation of the side effects of valproic acid and its serum level. Tiredness and impaired function of thrombocytes has been observed to be dependent on the valproic acid plasma level.