Monoamine Oxidase Inhibitors (MAOIs)



Phenelzine and Tranylcypromine (tran il SIP roe meen) are monoamine oxidase or MAO inhibitors. inhibition of the MAO enzyme increases levels of neurotransmitters, such as serotonin, dopamine and norepinephrine. MAOs are useful in treating atypical depression. A major adverse effect of taking these drugs is their ability to cause a hypertensive crisis after ingestion of tyramine containing foods like cheese. Another important side effect to remember is serotonin syndrome, which is more common if monoamine oxidase inhibitors are given with other serotonin-modulating drugs.

Key Points

  • Non-Selective Monoamine Oxidase Inhibitors (MAOIs)
    • Drug Names
      • Phenelzine
      • Tranylcypromine
      • Isocarboxazid
    • Mechanism
      • Cause non-selective inhibition of monoamine oxidase (MAO)
        • Increase levels of all monoamine neurotransmitters (norepinephrine, serotonin, and dopamine)
    • Indications
      • Treat Atypical Depression
        • Contrast vs. typical depression as atypical depression is associated with mood reactivity (can find enjoyment in positive things), leaden fatigue/paralysis (limbs feel like “lead”), rejection sensitivity, and reversed vegetative signs (increased sleep and appetite)
    • Adverse Effects
      • Causes Hypertensive crisis
        • Especially with the ingestion of tyramine,  which is found in cheeses, cured meats, draft beer, etc.
        • Tyramine is an amine which can displace NE and epinephrine from pre-synaptic vesicles into the neural synapse. However, tyramine is normally broken down by the MAO enzyme system before it achieves physiologically significant levels. In a patient on MAOIs, tyramine levels may build up, leading to high levels of NE and epinephrine release.
        • Resulting overload of catecholamines leads to hypertension and sympathetic hyperactivity
      • Causes Serotonin Syndrome
        • Characterized by fever, altered mental status, diaphoresis, and sympathetic hyperactivity.
        • Contraindicated with any other serotonin modulating drugs (e.g. SSRIs, TCAs)
        • Patients should wait 2 weeks after stopping MAOIs before starting any other serotonergic drugs to decrease the risk of serotonin syndrome