Plasma phenytoin in concentrations in epileptic patients (Hebrew)

Plasma phenytoin concentrations were determined by the gas chromatography method of Sine et al. in a group of 41 epileptic patients. In 19 patients the disease was not controlled by therapeutic doses of phenytoin and they had a mean drug concentration of 5.6 μg/ml, while in 22 patients in whom the disease was controlled, the mean drug concentration was 6.5 μg/ml. This difference was not significant. 3 patients presenting clinical signs of phenytoin intoxication had plasma levels above 19 μg/ml. Very low concentrations (below 2.5 μg/ml) were found in patients who were taking medication at a high phenobarbital/phenytoin ratio. This finding suggests increased catabolism of phenytoin induced by phenobarbital. The results raise the possibility that the drug in the usual dose (4 to 6 mg/kg) is not sufficiently effective.