Properties of the MAOI class of drugs
Drugs of the monoamine oxidase inhibitor (MAOI) type were among the first to be introduced clinically as antidepressants. They are now largely superseded by other types of antidepressants with improved efficacies and fewer side effects. Important examples are phenelzine and tranylcypromine. These bind covalently to the monoamine oxidase enzyme, resulting in non-competitive, irreversible inhibition; however, they do not distinguish between the two isozymes (MAO-A, MAO-B). Studies have demonstrated that the therapeutic effect of MAOIs is associated with MAO-A inhibition. This led to the development of moclobemide, which functions as a reversible, competitive inhibitor of MAO-A (RIMA). Clorgyline, although MAO-A-selective, is an irreversible inhibitor of the enzyme. The unwanted side effects of MAOIs include hypotension; atropine-like side effects (sympathomimetic effect); weight gain; and excessive CNS stimulation. The side effects associated with moclobemide are much milder than those reported with other MAOIs; they are also transient and disappear when treatment stops.
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References
Drugs used in affective disorders. In: Pharmacology, 4th edition. Rang HP, Dale MM and Ritter JM. Edinburgh, UK: Harcourt Publishers Ltd, 2001:550–565.
Antidepressants and mood stabilizers. In: Essential psychopharmacology. Neuroscientific basis and practical applications. Stahl SM. Cambridge, UK: Cambridge University Press, 1996:131–166.