Kinetics of CSF Phenytoin in Children

The efficacy of intravenous phenytoin for the treatment of status epilepticus is related to the rapid entry of phenytoin into brain parenchyma. There is no information concerning the correlation between phenytoin serum and CSF concentrations in children, and the application of CSF data to clinical use. We report 7 children (2–11 yrs) who were treated or exposed to phenytoin in doses between 10.5–230 mg/kg. Lumbar puncture was performed 9 times in 6 of the patients. In one patient, an intraventricular catheter permitted successive assessment of CSF phenytoin concentrations. The ratio of CSF/serum phenytoin concentrations was 0.16 ± 0.08, with gradual increase over the first 8 hours as the serum phenytoin concentration decreased. There was good correlation between therapeutic outcome and CSF phenytoin levels higher than 2 mcg/ml. In one patient the coma state secondary to phenytoin intoxication was associated with high CSF concentration (6 mcg/ml).