Monoamine oxidase inhibitor toxicity

Background

• Mono Amine Oxidase Inhibitors
• Used to treat depression and Parkinsonism (e.g. selegiline)
• Lead to increased norepinephrine, serotonin, dopamine, tyramine
• Toxicity often delayed 6-24 hours after ingestion

Clinical Features of Overdose

• Similar to hyperadrenergic state
• Severe toxicity accompanied by coma, seizure, bradycardia, hypotension, worsening hyperthermia

Differential Diagnosis

• Intoxications
  • Amphetamines
  • Antimuscarinics
• Withdrawal states
  • Ethanol
  • Clonidine
  • Beta-blockers
• Medical conditions
  • Heat stroke
  • Hypoglycemia
  • Hyperthyroidism
• Adverse drug reactions
  • Malignant Hyperthermia
  • Serotonin Syndrome
  • Tyramine Reaction
  • Neuroleptic Malignant Syndrome (NMS)

Treatment

• Gastric decontamination
  • Lavage indicated if can be performed <1 hour after ingestion
  • Activated charcoal x 1
• Supportive care
  • Hypertension
    • Treat only with short-acting agents: may develop precipitous hypotension
    • Phentolamine: 2.5-5mg IV bolus q15-15min; can also give as infusion 0.2-0.5mg/min
    • Nitroprusside: 1mcg/kg/min and titrate up
  • Hypotension: intravenous fluid +/- norepinephrine
  • Seizures: benzodiazepines are 1st line
  • Hyperthermia
    • Routine cooling measures
    • Consider paralysis if patient has persistent muscle rigidity

Disposition

• Admit all patients for 24 hour observation to monitored setting

Prevention

• Do not prescribe the following medications if a patient is taking a MAOI: meperidine, dextromethorphan, tramadol, propoxyphene, or cyclobenzaprine

See Also

• Tyramine Reaction
• Toxidromes