Department of Emergency Medicine

UMEM Educational Pearls

Category: Neurology

Title: Symptoms of Phenytoin Toxicity and Associated Levels

Keywords: phenytoin, dilantin, dilantin toxicity, ataxia, nystagmus (PubMed Search)

Posted: 9/9/2009 by Aisha Liferidge, MD (Updated: 4/26/2024)
Click here to contact Aisha Liferidge, MD

The following symptoms of phenytoin toxicity typically present initially, once plasma concentrations reach the listed levels below:

  • Nystagmus (on lateral gaze, at 20 mcg/mL)
  • Ataxia (at 30 mcg/mL)
  • Dysarthria and lethargy (at over 40 mcg/mL)


Other associated symptoms include tremor, hyper-reflexia, nausea, and vomiting.


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