[The serum concentration of anticonvulsants -- pharmacokinetic findings and practical therapeutic applications (author's transl)].

Routine determination of the blood serum concentration of most of the usual anticonvulsants is possible by means of an immunoenzymatic method (EMIT). Determination of the total concentration permits conclusions as to the amount of available, unbound and, thus, effective amount of the substance. Regular determination of serum values provides insight into the relevant pharmacokinetics. Metabolism of anticonvulsants differs greatly among individuals and therefore considerable individual variation exists in the relation between the applied dose and the attained serum level. The metabolic rate of the various substances is unequal and, accordingly, the time necessary to reach a steady state and the half life is very variable. Metabolism may be altered by various biological adaptations, diseases or other drugs, causing alterations in the serum level of the anticonvulsant. Results obtained to date indicate a therapeutic threshold concentration range. In a certain percentage of patients seizures are abolished or diminish in frequency only on attaining such a serum level. In more benign cases an adequate therapeutic effect may be obtained with lower ("subtherapeutic") concentrations, while on the other hand, in malignant cases, no efficient control of seizure activity can be attained even at a high serum concentration. The method should be used in all problematic patients. Up to 50% of patients with insufficient control of seizures show improvement or, even, absence of seizures if this method is included in the therapeutic concept.