[Serum phenytoin determination, its value in the treatment of epilepsy].

The concentration of phenytoin in serum was determined by gas chromatography for a total of 101 patients treated on an outpatient basis. In contrast to data reported in the literature, six patients (6 percent) showed therapeutically effective serum concentrations which were far below 7.0 microng/ml. In the majority of cases, however, the therapeutically effective range was from 7.0 to 20.0 microng/ml. A considerable reduction in the frequency of fits was obtained for 23 out of 32 patients who were treated in this manner. Examinations made on patients treated on an inpatient basis showed a definite correlation of daily dose, body weight, and serum concentration. However, interindividual differences were so high that the serum concentration cannot, in general, be safely concluded from the daily dose and body weight. Four percent of the patients showed toxic serum concentrations when normal doses of phenytoin were used. About 50 percent of the patients treated on an outpatient basis showed values indicating very irregular use of the drugs.