A case of phenytoin toxicity in a patient with advanced lung cancer

Abstract

Phenytoin is an anti-convulsant drug commonly used to prevent seizures in patients with cerebral metastases. Phenytoin has complicated non-linear kinetics, is highly protein bound and has a small window between its therapeutic and toxic dose. This combination of factors means that small increases in dosage can all too quickly result in high plasma levels and toxic symptoms. Symptoms of phenytoin toxicity include: confusion, nystagmus, agitation, abnormal gait and hallucinations.

This case report describes phenytoin toxicity in a patient receiving phenytoin 300mg three times a day for a number of weeks. The patient was admitted to the unit for terminal care, where his phenytoin levels were found to be very high. Phenytoin was withheld until levels returned to within the normal range. During this time the patient became orientated and many of his symptoms resolved.