Phenytoin Serum Levels in Children with Epilepsy: a Micro Immuno-assay Technique

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Abstract
The enzyme multiple immuno-assay technique (EMIT) was used to study phenytoin serum levels in 50 children with seizures. A single dose of phenytoin suspension or capsules (5 mg/kg per day) produced inadequate serum levels 16 and 24 h after ingestion; for this reason single dosage is not recommended. Twice-daily dosage of phenytoin suspension or capsules (5 mg/kg per day) produced adequate serum levels in most children throughout 24 h and this dosage is recommended. Twelve children continued to have seizures, but when the dose was increased to 10 mg/kg per day, 6 of the 12 obtained seizure control. Phenytoin reached equilibrium in the serum in 5 days, provided the child had not previously been taking phenobarbitone; 10 of 13 children who had been taking phenobarbitone did not achieve equilibrium of phenytoin in serum for 1-4 wk. Phenytoin suspension given twice-daily produced satisfactory serum levels provided the bottle was shaken well before dispensing. Apart from minor variations, phenytoin maintained its serum level during the 14-30 mo. follow-up period, whether 5 mg or 10 mg/kg per day of phenytoin was given.