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Monoamine oxidase inhibitors

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Monoamine oxidase inhibitors

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Questions

USMLE® Step 1 style questions USMLE

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USMLE® Step 2 style questions USMLE

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A 69- year-old woman is brought to the emergency room with her partner after losing consciousness at church. The partner states that there was no seizure-like activity, nausea, and vomiting. She regained consciousness 2 minutes after the syncopal episode. Her medical history includes atypical depression and GERD. Her current medication is a transdermal antidepressant that selectively inhibits MAOb receptors at low doses and is a nonselective MAO inhibitor at higher doses. Family history is noncontributory. She does not consume alcohol or use recreational drugs. She smokes 2-3 packs of cigarettes daily. Her temperature is 38.9°C (102°F), pulse is 110/min, respirations are 20/min, and blood pressure is 90/70 mmHg while standing and 110/70 mm of Hg while lying down. BMI is 20 kg/m2. She is awake, alert, and responds to commands and external stimuli. Pupils are equal and reactive. She moves all her extremities, and +2 reflexes are present throughout. The antidepressant used in this patient is also the agent of choice in the presence of which of the following additional findings on evaluation?

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Amines

MAO inhibitors p. 593

Anxiety

MAO inhibitors for p. 593

Dopamine p. 241, 332

MAO inhibitor effects p. 593

5-HT

MAO inhibitor effect on p. 593

Hypertensive crisis p. 587

MAO inhibitors as cause p. 593

MAO inhibitors p. 593

atypical depression p. 578

mechanism of p. 593

Parkinson disease p. 563

phobias p. 580

selegiline/rasagiline p. 564

tyramine and p. 243

Norepinephrine (NE)

MAO inhibitor effects p. 593

Serotonin syndrome p. 407, 562, 568, 587

MAO inhibitors p. 593

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Transcript

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Content Reviewers

Yifan Xiao, MD

Monoamine oxidase inhibitors, or MAOIs, are a class of medications used in the treatment of depression, which is a mood disorder that causes a persistent feeling of sadness and loss of interest in everyday activities.

Even though the exact cause of depression is still unknown, there is some evidence that suggests it’s related to low levels of serotonin, norepinephrine, and dopamine, which are also called monoamines because they have only one amine group.

Now, monoamine oxidase inhibitors work by increasing levels of serotonin, norepinephrine, and dopamine, which helps to alleviate the symptoms of depression.

Alright, now within the brain, there are many different types of neurons, but we’re going to focus only on three: serotonergic neurons that release serotonin, noradrenergic neurons that release norepinephrine, and dopaminergic neurons that release dopamine.

Each of these neurons synthesizes and stores neurotransmitters in small vesicles, so when an action potential reaches the presynaptic membrane, these vesicles fuse with the membrane, releasing neurotransmitters in the synaptic cleft.

Serotonergic neurons release serotonin, which then binds to 5-HT2 receptors, thereby increasing neural stimulation and regulating mood, feeding, and reproductive behavior.

On the other hand, noradrenergic neurons release norepinephrine, which hooks up to norepinephrine receptors (NE receptors), boosting alertness and focus.

Lastly, dopaminergic neurons release dopamine, which binds to dopamine receptors, stimulating cognitive functions, motivation, and awakeness.

As long as there’s a high enough concentration of neurotransmitters in the synaptic cleft, the postsynaptic neurons will continue to fire.

Now, each of these presynaptic neurons has small reuptake proteins, which pump the neurotransmitters from the synaptic cleft back into presynaptic neurons.

Once inside the neuron, a class of enzymes called monoamine oxidases will break down some of these neurotransmitters; monoamine oxidase A breaks down serotonin, norepinephrine, and dopamine; and monoamine oxidase B only breaks down dopamine.

Summary

Monoamine oxidase inhibitors (MAOIs) are a class of medications used to treat depression, anxiety, and other mental health disorders. MAOIs work by blocking an enzyme called monoamine oxidase, which breaks down monoamine neurotransmitters, namely serotonin, norepinephrine, and dopamine, so they can be released again into the synapse. By blocking this enzyme, these chemicals are able to remain at higher levels in the brain, providing a beneficial effect on mood and behavior. Common side effects of MAOIs include drowsiness, dizziness, insomnia, dry mouth, and weight gain.

Sources

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  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "Neuroleptic malignant syndrome and serotonin syndrome" Thermoregulation: From Basic Neuroscience to Clinical Neurology, Part II (2018)
  5. "Mechanism of action of antidepressant medications" J Clin Psychiatry (1999)
  6. "Atypical Depression" CNS Drugs (2009)