[Problems in serum-level determination during valproic acid therapy].

An investigation was carried out to determine whether or not a reliable and reproducible steady state serum level of the anticonvulsant drug valproic acid could be found, such that single values of a serum level determination could be used in therapeutic control. 1. A reliable and comparable serum concentration of valproic acid could not be found in 11 patients during a long-term investigation over a period of 8 weeks. Likewise this could not be found in the 24-h serum concentration profile in 8 of the above mentioned patients, who were receiving both mono and combined therapy. 2. The half-life values for valproic acid in these 8 patients lay between 8--12.5 h. 3. The maximum concentration of valproic acid lies in unforeseeable time spans after drug administration. 4. The morning fasting values are comparable only to a limited extent. In future daily profiles it must be decided whether, and if so to what extent, valproic acid serum concentration determinations can be of value to the individual treatment of epileptics.