Phenytoin serum levels in children with epilepsy: a micro immuno-assay technique.

The enzyme multiple immuno-assay technique (EMIT) was used to study phenytoin serum levels in 50 children with seizures. It was found that: (1) a single dose of phenytoin suspension or capsules (5mg/kg/day) produced inadequate serum levels 16 and 24 hours after ingestion, and for this reason single dosage is not recommended; (2) twice-daily dosage of phenytoin suspension or capsules (5mg/kg/day) produced adequate serum levels in most children throughout the 24 hours, and this dosage is recommended; (3) 12 children continued to have seizures but when the dose was increased to 10mg/kg/day six of the 12 obtained control of seizures; (4) phenytoin reached equilibrium in the serum in five days provided the child had not previously been taking phenobarbitone; (5) of 13 children who had been taking phenobarbitone, 10 did not achieve equilibrium of phenytoin in serum for one to four weeks; (6) phenytoin suspension given twice-daily produced satisfactory serum levels provided the bottle was shaken well before dispensing; (7) apart from minor variations, phenytoin maintained its level in serum during the 14 to 30 months follow-up period, whether 5mg or 10mg/kg/day of phenytoin was given.