Learning objectives

• Diagnose and treat MAOI toxicity

Definition and mechanisms

• Monoamine oxidase inhibitors (MAOIs) are a class of antidepressants
• MAOIs prevent the breakdown of monoamine neurotransmitters serotonin and norepinephrine and thereby increasing their availability
• MAOIs interact severely with commonly used anesthetic agents 
• MAOI toxicity can be difficult to distinguish from much more common clinical entities
• Without MAO to break down epinephrine, norepinephrine, dopamine, serotonin, and tyramine, the storage, and release of these monoamines are increased
• In this way leading to tachycardia, hyperthermia, myoclonus, hypertension, and agitation
• Plasma concentrations peak within two to three hours
• Three ways in which MAOI toxicity can occur:
  • Drug-food interaction with tyramine-containing foods
    • When MAO found in the gut and liver is inhibited, dietary tyramine indirectly causes an amplification of adrenergic activity
    • Aged cheeses, beer wine, ginseng, avocado
  • Overdose as MAOIs have a low therapeutic index
  • Drug-drug interaction when a MAOI is combined with other agents that increases the synthesis, release, and effect or decreases the metabolism or reuptake of monoamines
    • Dextromethorphan, linezolid, methylene blue, selective serotonin reuptake inhibitors, serotoninergic agents, and tramadol

Signs and symptoms

• MAOI toxicity can present with diaphoresis whereas an anticholinergic syndrome should have dry skin
• MAOI toxicity is much more likely to present with generalized or ocular clonus than neuroleptic malignant syndrome

Diagnosis

• History and physical examination
• Frequent temperature measurements
• Electrolytes and lactic acid
• Salicylate, acetaminophen, and alcohol levels should be obtained

Management

Anesthetic management

• Consider risk of serotonin syndrome if combined with other serotonergic agents
• Risk of hypertensive crisis
  • Avoid indirect sympathomimetics, caution with direct agents
  • Avoid cocaine
• See monoamine oxidase inhibitors

Suggested reading

• Bartakke, A., Corredor, C., Van Rensburg, A., 2020. Serotonin syndrome in the perioperative period. BJA Education 20, 10–17.
• Peck T, Wong A, Norman E. 2010. Anaesthetic implications of psychoactive drugs. Continuing Education in Anaesthesia Critical Care & Pain.10;(6); 177-181.
• Gillman, P.K., 2005. Monoamine oxidase inhibitors, opioid analgesics and serotonin toxicity. British Journal of Anaesthesia 95, 434–441.