A small and usually clinically unimportant rise in
phenytoin levels may occur if
metronidazole is given with
phenytoin, although a few patients have developed
phenytoin toxicity. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
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.