Phenytoin toxicity occurred in a patient given
capecitabine. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
As this interaction is in line with the way fluorouracil interacts, it would seem prudent to warn the patient to monitor for signs of
phenytoin toxicity (blurred vision, nystagmus, ataxia or drowsiness). Take
phenytoin levels and adjust the dose as necessary.