Drug interaction between phenytoin and valproic acid in a child with refractory epilepsy: a case report.

Introduction: There are no published reports on pediatric phenytoin toxicity, resulting from the drug interaction between phenytoin and valproic acid.

Case Description: A 12-year-old patient with refractory epilepsy syndrome presented with phenytoin toxicity, following a concomitant treatment with phenytoin, valproic acid, and lamotrigine. The phenytoin concentration detected in the capsules used by the patient was in accordance with the prescribed dose and was appropriate for the age and weight of the patient.