[Plasma concentration of phenytoin in epileptics--importance for the clinician]

Plasma concentrations of diphenylhydantoin were determined by the method of Wallace (double extraction, spectrophotometry) in 150 samples taken from 121 epileptic patients. They correlated well with those determined by gas chromatography, were not dose-dependent and were often below 10 mul/ml. They were above 20 mul/ml in 6 patients with CNS intoxication. These determinations were also useful for detecting patients who did not take the drug as prescribed (14 suspected cases, 4 confirmed). However, blood levels did not seem to offer an accurate index of the effectiveness of diphenylhydantoin.