PHENYTOIN (Dilantin)

Name: PHENYTOIN (DilantinR)
Classification: anticonvulsant; antiarrhythmic
  • treatment or prophylaxis of tonic-clonic seizures
  • management of status epilepticus
  • treatment of ventricular tachycardia and paroxysmal tachycardia especially secondary to digoxin toxicity
  • Loading Dose: 
    • 14-18mg/kg IV direct
  • Maintenance Dose:
    • 5mg/kg/day (in divided doses every 8 hours)
  • IV Direct:
    • preferred route of administration; rate not to exceed 50mg/min
  • IV Infusion:
    • must be mixed in sodium chloride 0.9% or Ringer's Lactate; do not mix with dextrose solutions as precipitation will occcur
    • concentration of 1-20mg/ml; rate not to exceed 50mg/min 
    • must be administered with a filter; a TPN set can be used and changed with the same frequency of other line changes
    • administer at slower rate if patient is receiving dopamine or in the presence of cardiovascular instability
    • IV line to be flushed with NS or RL before and after phenytoin administration
    • use prepared solutions immediately
Adverse Effects:
  • hypotension
  • decreased automaticity of ventricles in second and complete AV heart block (suppression of ventricular escape rhythm)
  • hyperglycemia 
  • nystagmus
  • folic acid deficiency; megaloblastic anaemia
  • nausea
  • seizures (abrupt withdrawal may precipitate peripheral neuropathy seizure)
  • rash
  • lymphadenopathy
  • gingival hyperplasia
Drug Interactions:
  • phenytoin + dopamine = increased hypotension
  • phenytoin + theophylline = decreased theophylline effect
  • phenytoin + dexamethasone = decreased dexamethasone effect
  • phenytoin + quinidine = decreased quinidine effect
  • phenytoin + amiodarone = increased phenytoin level
  • phenytoin + fluconazole = increased phenytoin level
Monitoring Therapy:
  • BP
  • HR and rhythm
  • seizure activity
  • neurological signs
  • phenytoin levels: therapeutic 40 - 80 uM/L (pre-dose), toxic > 80 uM/L (need to adjust for low serum albumin and/or high urea levels, which will increase the free fraction of phenytoin leading to an increased amount of drug available for activity)
  • draw levels immediately before next scheduled dose, or at least 4-6 hours post administration
Adult Critical Care Protocol:
  • May be administered by IV infusion and titrated by a nurse in Adult Critical Care
  • May be administered IV direct by a nurse in Adult Critical Care provided that the rate does not exceed 50 mg/min

Lynne Kelly, Pharmacist, CCTC
Brenda Morgan, Clinical Nurse Specialist, CCTC
Last Update: September 20, 2018