Serum phenytoin concentrations in paediatric patients following intravenous loading.

Phenytoin is used to treat acute tonic-clonic seizures in children who have not responded to a benzodiazepine. In the UK, the loading dose of phenytoin is 18 mg/kg. There is limited evidence on whether this loading dose will achieve the desired levels in paediatric patients. Intravenous loading doses of phenytoin were retrospectively and prospectively audited over 19 months. Doses were normalised for weight and compared with the serum phenytoin concentrations. Errors in dose calculations and adverse events were recorded. Serum phenytoin concentrations were measured on 31 occasions in 27 children (24 retrospective and 10 prospective) between 60 and 180 (median, 153) min after completion of the loading dose. Serum phenytoin concentrations were within the therapeutic range (10-20 μg/ml) on 24 occasions. No errors in dose calculations or adverse effects were identified. A phenytoin loading dose of 18 mg/kg gave serum concentrations within the recommended therapeutic range in most children.