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
  • Nausea and vomiting
• 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

Toxicity symptoms by phenytoin level^

Level	Sypmtoms
>10	Usually no symptoms
10-20	Occasional mild nystagmus
20-30	Nystagmus
30-40	Ataxia, slurred speech, Nausea/vomiting
40-50	Lethargy, confusion
>50	Coma, seizure (rare)

^Provides a rough guide only; neither sensitive nor specific

Treatment

• Detoxification
  • Activated charcoal PO
• Bradyarrhythmias
  • Atropine, pacing
• Hypotension
  • IVF

Disposition

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

See Also

• Phenytoin