Severe osteomalacia and rickets have been seen in a few patients taking
phenytoin with
acetazolamide. Rises in
phenytoin levels have also been described in a very small number of patients. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
The
clinical importance of this interaction is unknown, but bear it in mind in case of an unexpected response to treatment. Indicators of
phenytoin toxicity include blurred vision, nystagmus, ataxia or drowsiness.