Drug Interaction Report

MONITOR: Topiramate administered with phenytoin has been reported to have led to a 25% increase in phenytoin plasma concentrations, particularly in those patients receiving phenytoin twice a day. Additionally, the concentration of topiramate decreased by 48%. Topiramate may decrease the metabolism of phenytoin (or other hydantoins) while hydantoins may increase the metabolism of topiramate.

MANAGEMENT: Patients should be closely observed for clinical response and signs of hydantoin toxicity if these drugs must be given concurrently and serum concentrations should be monitored. Patients should be advised to notify their physician if they experience loss of seizure control or symptoms of hydantoin toxicity, including drowsiness, visual disturbances, change in mental status, seizures, nausea, or ataxia. Addition or withdrawal of hydantoins during therapy with topiramate may require a dose adjustment of topiramate and/or the hydantoin.