PHENYTOIN AND ZONISAMIDE
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).
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).