How high can we go with phenytoin?

Eran Kozer, Shahid Parvez, Berge A. Minassian, Jeff Kobayashi, Zul Verjee, Gideon Koren

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Phenytoin is an effective anticonvulsant, but high serum phenytoin concentrations may be associated with serious toxicity. The upper limit for the therapeutic serum concentration of phenytoin is considered to be 80 μmol/L. However, in some situations higher serum concentrations are needed to control seizures. The authors describe a 9-year-old girl who needed concentrations twice the normal amount to control recurrent episodes of decreased levels of consciousness. Except for nystagmus, she had no other signs of phenytoin toxicity. This patient highlights the critical principle in therapeutic drug monitoring of individualizing drug therapy. Although some patients receiving phenytoin may achieve seizure control with "subtherapeutic" levels (i.e., <40 μmol/L), others may need supratherapeutic levels, as was the case with this patient. Clinicians should be careful not to treat "numbers" (i.e., serum concentrations), but rather the patient's clinical condition, with a careful balance between therapeutic advantage and adverse effects.

Original languageEnglish
Pages (from-to)386-389
Number of pages4
JournalTherapeutic Drug Monitoring
Issue number3
StatePublished - 2002
Externally publishedYes


  • Child
  • Drug monitoring
  • Phenytoin


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