Felbamate causes a moderate increase in
serum phenytoin levels.
Phenytoin dosage reductions of 10 to 40% have been required to manage this interaction.
Felbamate serum levels are reduced but the importance of this is uncertain.
Warn the patient to monitor for indicators of
phenytoin toxicity (blurred vision, nystagmus, ataxia or drowsiness). Take
phenytoin levels and adjust the dose as necessary.