Preliminary evidence suggests that
clarithromycin may raise
serum phenytoin levels. 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. Note that
erythromycin does not appear to interact.