Acute phenytoin intoxication: causes, symptoms, misdiagnoses, and outcomes

Phenytoin is a commonly prescribed antiepileptic drug. Due to its saturation (zero-order) pharmacokinetics, phenytoin carries a special risk of dose-related toxicity that is an important issue in emergency medicine. The purpose of this cross-sectional case-series study was to investigate the causes, symptoms, misdiagnoses, and outcomes of acute phenytoin intoxication. It was based on a retrospective chart review of 30 inpatients (mean age, 41.6 +/- 22.8 years) with 36 episodes of acute phenytoin intoxication at our university hospital in the past 13 years. The average initial serum phenytoin level was 47.3 +/- 9.7 microg/mL (range, 27.9-70.4 microg/mL). Excessive self-medication, misunderstanding of the prescription order, and probable drug interaction were the three leading causes of acute phenytoin intoxication. Unsteady gait, dizziness/vertigo, nausea/vomiting, general weakness, and drowsiness were the most common presenting symptoms. The tentative diagnostic accuracy was 67%. The most common initial misdiagnosis was brainstem or cerebellum stroke (14%). The clinical course in all patients was uneventful under temporary withdrawal of phenytoin and supportive care. We concluded that acute phenytoin intoxication was relatively under-diagnosed in the emergency service. Although acute phenytoin intoxication causes no mortality and has a good outcome, the unsteady gait increases the risk of injuries caused by falls. The management of acute phenytoin intoxication includes temporary withdrawal of phenytoin and supportive care.