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

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

Treatment

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

Disposition

• Admit all patients for 24 hour obsservation

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

Source

• Tintinalli