A Study on the Serum Level of Phenytoin after Intravenous Administration of Loading Dose

ABSTRACT

PURPOSE: Phenytoin is effectively and widely used drug for the treatment of status epilepticus and patient with ongoing seizure by intravenous infusion. It is generally recommended to maintain serum concentration above 10microgram/ml for the sustained effective anticonvulsant effect. This study was designed to know the optimal time to begin oral maintenance therapy after initial intravenous infusion. METHODS: Total 17 patients with status epilepticus and ongoing seizure who were admitted to the pediatric department of Han Yang University during the period from July 1993 to September 1995 were enrolled in this study and serum level was monitored at 2, 6 and 12 hours after the intravenous phenytoin infusion of loading dose, 20mg/kg of body weight by enzyme multiplict immunoassay technic. Student t-test was used for statistical analysis and P value below 0.05 interpreted as statistically significant. RESULTS: 1) The subjects were 5 boys and 12 girls, average age was 7.6 years old and age distribution was from 3 months to 15 years old. 2) The serum concentration ranged from 9.42microgram/ml to 43.98microgram/ml (24.04+/-8.97microgram/ml) after 2 hours, 8.82microgram/ml to 33.95microgram/ml (18.62+/-6.43microgram/ml) after 6 hours, and 7.20microgram/ml to 31.38microgram/ml (14.97+/-6.58microgram/ml) after 12 hours. 3) There was no significant differences of average serum concentration and the decline of serum concentration by time between patients over and below 2 years of age and both sexes. 4) The average decrease in serum phenytoin concentration per hour was 0.91microgram/ml. 5) The average maintenance duration of therapeutic serum level after initial infusion of loading dose was 22.4 hours. CONCLUSIONS: The average maintenance duration of therapeutic serum level after initial infusion of loading dose was 22.4 hours, hence it would be appropriate to administer maintenance dose of phenytoin if the serum level at 2 hours after loading dose is satisfactory.