Phenytoin toxicity

Background

• Mortality is extremely rare after intentional overdose if good supportive care is provided
• Rapid IV dosing carries greatest risk (due to propylene glycol constituent of IV form --> myocardia depression & cardiac arrest)
• 90% protein bound; dialysis ineffective

Clinical Features

• CV (only with IV form)
  • Bradycardia
  • Hypotension
  • Vfib
  • Asystole
• Neuro
  • Nystagmus
    • First only with forced lateral gaze; later becomes spontaneous
    • May disappear at higher levels
  • Ataxia
  • Decreased LOC
• GI
  • N/V
• Skin
  • tissue infiltration (IV) --> "purple glove syndrome"
  • edema, pain, ischemia, tissue necrosis, compartment syndrome
• Anticonvulsant hypersensitivity syndrome
  • Eosinophilia, rash, pseudolymphoma, SLE, pancytopenia, hepatitis, pneumonitis

Diagnosis

• Phenytoin level
  • Provides a rough guide only; neither sensitive nor specific
  • Level >10: usually no symptoms
  • Level 10-20: Occasional mild nystagmus
  • Level 20-30: Nystagmus
  • Level 30-40: Ataxia, slurred speech, N/V
  • Level 40-50: Lethargy, confusion
  • Level >50: Coma, seizure (rare)

Treatment

1. Detoxification
   1. Activated charcoal PO
2. Bradyarrhythmias
   1. Atropine, pacing
3. Hypotension
   1. IVF

Disposition

• Cannot base on phenytoin level (erratic absorption after PO overdose)
  • Consider discharge if pt has only mild symptoms and serial phenytoin levels decline

Source

Tintinalli