Phenytoin Intoxication: Burden and risk factors

The aim of the study is to determine: 1) the frequency of patients admitted for phenytoin toxicity and their economic burden; 2) the clinical symptoms and signs of intoxication; 3) the causes or risk factors of intoxication, and 4) the ways to prevent phenytoin toxicity.

Retrospective review of hospital ICD coded database between 1987 and 1998. All patients with phenytoin intoxication were reviewed.

Thirty-one patients were admitted 35 times for phenytoin toxicity. Phenytoin intoxication accounted for 1/5,000 admissions. Ataxia, confusion, dysarthria and nystagmus were the most common signs. The outcome was benign except for one patient who remained with a residual cerebellar syndrome. Unawareness of phenytoin pharmacokinetics, lack of clinic follow-up visits, infrequent serum level monitoring following drug dosage change and using wrong doses accounted for most of the cases.

Phenytoin intoxication rarely leaves any permanent sequelae but can be a cause of significant transient morbidity and prolonged hospitalization. As the major causes were related to poor follow-up or were iatrogenic, a better patient education and a stepwise dose increase based on serum level, together with drug level monitoring 2-4 weeks after dose change could decrease the incidence and severity of phenytoin intoxication.