MAOI toxicity

Learning objectives

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

Mild signs	Agitation Diaphoresis Tachycardia Mild temperature elevation
Moderate signs	Altered mental status Tachypnea Vomiting Dysrhythmias Hypertension
Severe signs	Severe hyperthermia Seizures Central nervous system (CNS) depression Coma Cardiorespiratory depression Muscle rigidity Myoclonus

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

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