Therapeutic drug monitoring
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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 micromol/L. However, in some situations higher serum concentrations are needed to control seizures. ⋯ 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 micromol/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.