Key investigations

Key investigations for phenytoin poisoning are:

• serum phenytoin concentration (see also Toxic concentration)
  • useful to confirm an acute ingestion, confirm that cerebellar toxicity is related to chronic phenytoin therapy, and identify slow metabolisers of phenytoin
  • treatment for phenytoin toxicity should be based on clinical assessment rather than serum phenytoin concentration
  • serial serum phenytoin concentrations are used to monitor for resolution of severe phenytoin toxicity, but have no role in mild or moderate toxicity
• serum electrolyte, urea and creatinine concentrations
• blood glucose concentration
• electrocardiogram (ECG).