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Monoamine Oxidase Inhibitor

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Monoamine Oxidase Inhibitor, MAO inhibitor, Phenelzine, Nardil, Tranylcypromine, Parnate

  • Indications
  • Comorbid Depression
  • Mechanism
  1. Inhibits monoamine oxidase
    1. Monoamine Oxidase is enzyme that breaks down biogenic amines (e.g. Norepinephrine, Serotonin, Dopamine)
    2. Type A Monoamine Oxidase affects Gastrointestinal System
    3. Type B Monoamine Oxidase affects central nervous system
    4. Older MAO inhibitors are nonspecific and affect both Type A and B (e.g. trancypromine, Phenelzine)
    5. Selegiline is specific for Type B and is used in Parkinsonism
  2. Increases synaptic concentration of monoamines
    1. Serotonin
    2. Norepinephrine
  • Precautions
  1. Tyramine-free diet must be followed
    1. Continue for two weeks after stopping medication
    2. See Tyramine Containing Foods
  2. Stop 2 weeks before starting another Antidepressant
  3. Taper Nardil slowly when stopping
    1. See Antidepressant Withdrawal
    2. Reduce dose by 15 mg/day every 2 weeks (or 10%/week)
  • Preparations
  • Hydrazine
  1. Isocarboxazid (Marplan): No longer manufactured in U.S.
    1. Dosing: 10 mg PO bid
    2. Maximum: 60 mg per day
  2. Phenelzine (Nardil)
    1. Dosing: 15 mg PO tid
    2. Maximum: 90 mg per day
  • Preparations Non-hydrazine
  1. Tranylcypromine (Parnate)
    1. Dosing: 10-40 mg/day in divided doses
    2. Maximum: 60 mg per day
  2. Parkinsonian agents
    1. Selegiline (Eldepryl)
  • Preparations
  • Other agents with MAO inhibitor Activity
  1. Linezolid
  2. St John's Wort
    1. Contains Hypericin and Hyperforin (weak Type A and B MAO inhibitors)
  • Complications
  1. Hypertensive Crisis (life-threatening)
    1. Occurs if tyramine or Sympathomimetic exposure
    2. Treat with phentolamine (alpha-adrenergic antagonist)
  2. Hypotension to cardiovascular collapse (occurs with Overdose)
    1. Treat with Intravenous Fluids and direct acting Vasopressors (e.g. Norepinephrine)
  3. Serotonin Syndrome
    1. Occurs with concurrent use of other Serotoninergic drug, or in Overdose
  • Drug Interactions (Do not use with these medications)
  • Adverse Effects
  1. Anti-Histaminergic effects
    1. Dizziness
    2. Sedation
    3. Orthostatic Hypotension
    4. Weight gain
  2. Dopaminergic effects
    1. Insomnia
    2. Myoclonal jerks
  3. Serotoninergic Effects
    1. Sexual Dysfunction
    2. Headache
  4. Anticholinergic Toxicity
    1. Dry Mouth
    2. Constipation
    3. Blurred Vision
    4. Urinary hesitancy
    5. Nausea
    6. Memory Dysfunction
  5. Other Effects
    1. Peripheral Edema
    2. Weakness
  • References
  1. Nordt and Shoenberger in Herbert (2019) EM:Rap 19(3): 8-9