Phenytoin toxicity in two-month-old Thai infant with CYP2C9 gene polymorphism--A case report.

Phenytoin is one of the most well established and most effective antiepileptic medications for the treatment of focal seizures. In our clinical practice, it has proven difficult to maintain therapeutic phenytoin levels in infants less than three months of age. Incidence of phenytoin toxicity in infants is very rare. The cytochrome P450 super family plays an important role in phenytoin metabolism, especially CYP2C9 and CYP2C19. In this case report, we profiled a two-month-old Thai infant who developed phenytoin toxicity resulting from CYP2C9 gene polymorphism.