Mechanism of action:
This group of drugs called monoamine oxidase inhibitors (MAIOs) inhibits monoamine oxidase, the enzyme that terminates the actions of neurotransmitters such as dopamine, norepinephrine, epinephrine, and serotonin. This creates the higher level of the neurotransmitters in the CNS to facilitate neurotransmission and alleviate the symptoms of depression. Because of their low safe margin, these drugs are reserved for patients who have not responded to tricyclic antidepressants, or SSRIs.

  • Isocarboxazid
  • Phenelzine
  • Tranycypromide

Side effects:

  • Drowsiness
  • Insomnia
  • Orthostatic hypotension
  • Blurred vision
  • Nausea
  • Constipation
  • Anorexia
  • Dry mouth
  • Urinary retention
  • Suicidal ideation
  • Serotonin syndrome

A common concerns is that this drugs affects the large numbers of foods and other medications, sometimes with serious effects.

A hypertensive crisis can occur when it is given with other antidepressants or sympathomimetics drugs.

MAIOs + SSRIs drugs = serotonin syndrome

MAIOs + antihypertensive drugs = severe hypotension

MAIOs + oral hypoglycemic agents or insulin = potentiate the effect of oral hypoglycemic effects.

MAIOs + meperdine or dextromethorphan = Hyperpyrexia

A hypertensive crisis can also result from an interaction between MAIOs and foods containing tyramine, a form of the amino acid tyrosine. Tyramine usually degraded by the MAIO in the intestine. If patient takes MAIOs however, tyramine enters bloodstreams in high concentration and displaces norepinephrine within presynaptic nerve terminals. The result is a sudden release of norepinephrine, causing acute hypertension. Side effects can occur in the minutes of ingestion of food. Myocardial infarction and cerebral accidents can occur. A calcium channel blockers are given as an antidotes.