A study found that
omeprazole 20 mg daily did not affect
phenytoin levels, whereas earlier studies suggested that
phenytoin levels might be modestly raised by
omeprazole 40 mg daily. A study with esomeprazole also suggests that it may cause a minor rise in
phenytoin levels. Lansoprazole does not normally interact with
phenytoin, but an isolated case report of
toxicity is tentatively attributed to an interaction. Fosphenytoin, a prodrug of
phenytoin, may interact similarly with these
proton pump inhibitors.
This interaction is unlikely to be generally significant, but bear it in mind in case of an unexpected response to treatment. Indicators of
phenytoin toxicity include blurred vision, nystagmus, ataxia or drowsiness. However, note that the manu- facturers of esomeprazole recommend monitoring
phenytoin levels.