Monoamine Oxidase Inhibitors (MAOIs)

Monoamine oxidase inhibitors (MAOIs) are a class of medications that suppress or inhibit the activity of enzymes called monoamine oxidases. They can be used to treat neurological conditions such as anxiety and depression in patients with aromatic l-amino acid decarboxylase (AADC) deficiency.

How do MAOIs work?

AADC, the enzyme that is missing or not fully functional in AADC deficiency, plays a crucial role in the production of two neurotransmitters or cell signaling molecules in the brain: dopamine and serotonin. Dopamine is also used by the body to produce the neurotransmitters epinephrine and norepinephrine.

AADC deficiency, therefore, causes severe deficits in the levels of dopamine, serotonin, epinephrine, and norepinephrine in the brain. This results in developmental delays, hypotonia (low muscle tone), movement disorders, and neurological problems such as anxiety and depression. The goal of AADC treatments is to restore or replenish the levels of these neurotransmitters.

Monoamine oxidases A and B are enzymes that degrade dopamine, serotonin, and norepinephrine, and play a role in maintaining the appropriate levels of these neurotransmitters. However, in AADC deficiency, their activity can further deplete these neurotransmitters below normal levels.

MAOIs prevent the degradation of dopamine, serotonin, and epinephrine in the brain by blocking the activity of monoamine oxidases. In this way, they increase the levels of these neurotransmitters, thereby alleviating the neurological symptoms of AADC deficiency, specifically anxiety and depression.

MAOIs and AADC deficiency

MAOIs have been extensively used as antidepressants and antianxiety medications. However, their efficacy in patients with AADC deficiency is unclear. They may be effective in patients with mild or moderate — but not severe — disease. They may also improve hypotonia in some patients but have no effect on other symptoms. Evidence suggests their use produces no clinical improvement or only short-term improvements.

According to the consensus guideline for the diagnosis and treatment of AADC deficiency, patients can be given a trial of MAOIs such as Nardil (phenelzine), Emsam (selegiline), and Parnate (tranylcypromine). However, care needs to be taken as they are known to interact adversely with certain foods and other medications.

Other information

MAOIs are associated with several side effects. The most common are dry mouth, nausea, diarrhea, constipation, drowsiness, insomnia, dizziness, and/or lightheadedness. MAOIs should be avoided for at least 10 days before any surgery to prevent adverse interactions with other medications taken before, during, or after surgery.

While taking MAOIs, foods with high levels of tyramine should also be avoided. Tyramine is an amino acid derivative that regulates blood pressure. Foods that are high in tyramine include aged cheeses, sauerkraut, cured meats, draft beer, and fermented soy products such as soy sauce, miso, and tofu. Restricting alcohol consumption may also be recommended for patients while they’re being treated with MAOIs.

MAOIs can interact with certain medications — including other antidepressants, painkillers, cold and allergy medications, and herbal supplements (such as St. John’s wort) — and cause high levels of serotonin, which can lead to a potentially life-threatening condition called serotonin syndrome. Adverse effects of the syndrome include tremors, high blood pressure, rapid heart rate, high fever, anxiety, confusion, and sweating.


Last updated: Sept. 19, 2019


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