Clinical presentation

Acute phenytoin toxicity is apparent within several hours after ingestion, evolves gradually thereafter, and resolves as drug elimination occurs over several days to weeks.

Effects of phenytoin poisoning include:

• central nervous system (CNS) effects
  • cerebellar toxicity—ataxia, dysarthria and nystagmus
  • confusion
  • CNS depression (altered conscious state ranging from drowsiness to coma)
  • seizures
• cardiovascular effects
  • conduction defects and arrhythmias are rare
  • bradycardia, hypotension and ventricular arrhythmias can occur after rapid intravenous administration of large doses, but are likely to be due to the propylene glycol diluent rather than phenytoin itself
• other effects—nausea.

Chronic phenytoin toxicity is usually associated with a history of dose escalation or repeated supratherapeutic ingestions. Patients present with gradually evolving confusion and cerebellar toxicity.