Nonselective Monoamine Oxidase Inhibitors

Monoamine oxidase inhibitors (MAOIs) are a rarely used class of antidepressant medications. MAOIs have significant side effects when used with certain foods or in combination with other medications.  

MAOIs inhibit monoamine oxidase enzymes in the gut. Monoamine oxidase enzymes in the gut typically metabolize tyramine, and inhibition results in higher levels of tyramine. Tyramine stimulates the release of catecholamines, which can result in a hypertensive crisis.  Tyramine is found in high levels in aged cheeses, meats, red wines, and smoked fish.  

Additionally, MAOIs can interact with other antidepressants and over the counter medications, which can result in serotonin syndrome due to excess serotonin.  MAOIs cannot be administered with SSRIs, TCAs, and certain opioids (meperidine, fentanyl).

Class Drugs

• Phenelzine

• Tranylcypromine

• Isocarboxazid

Class Mechanism of Action

MAO (monoamine oxidase) Inhibition

• MAO oxidizes excess neurotransmitters, which results in their inactivation.

• Most drugs form complexes with MAO causing irreversible inactivation.

• Increases neurotransmitter levels such as serotonin, dopamine, and NE.

Class Application

Depression

• Effects take weeks to see results.

• Rarely used due to food and drug interactions.

• There should be a 2-week delay in initiating new antidepressants after stopping an MAOI due to the time needed to regenerate MAO enzymes.

Class Adverse Effects

Food-food interactions

• Tyramine is contained in aged cheeses and meats, red wines, and smoked fish and is normally inactivated in the gut.

• When taking MAOI, gut MAO enzymes are also inhibited resulting in un-metabolized tyramine.

• Tyramine causes release of catecholamines resulting in a hypertensive crisis.

Possible outcomes are stroke, headache, stiff neck, cardiac arrhythmias, and seizures.

• Managed with alpha blockers (phentolamine and prazosin)

Serotonin Syndrome

• Co-administration of other anti-depressants is contraindicated.

• Unsafe levels of serotonin may result in serotonin syndrome.

Hyperthermia

• Hyperreflexia

• Myoclonus

• Tachycardia

• Diaphoresis

• Vomiting

• Diarrhea

Orthostatic hypotension

Dry mouth

Blurred vision

Drug Table

Drug Name	Application	Comments	Image
Isocarboxazid			"I sewing" "Car" "Acid"
Phenelzine		Sexual Dysfunction	"Funnel" "Scene"
Tranylcypromine			"Transylvanian Vampire" bear "Professional" "Be Mine heart"