Phenytoin can cause a small to moderate reduction in the
serum levels of
zonisamide.
Zonisamide appears not to affect
phenytoin levels in most studies, although two studies suggest a modest rise of about 20% may occur. Fosphenytoin, a prodrug of
phenytoin, may interact similarly
The general importance of this interaction is unknown although a serious interaction is unlikely. Consider the importance of a possible reduction in
zonisamide levels. Bear the potential for a modest increase in
phenytoin levels in mind should a patient taking
zonisamide develop signs of
phenytoin toxicity (blurred vision, nystagmus, ataxia or drowsiness).