Monoamine oxidase inhibitors

Monoamine oxidase inhibitors (MAOIs) are a class of drugs that inhibit the activity of one or both monoamine oxidase enzymes: monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B). They are best known as powerful anti-depressants, as well as effective therapeutic agents for panic disorder and social phobia. They are particularly effective in treatment-resistant depression and atypical depression. They are also used in the treatment of Parkinson's disease and several other disorders.

History

The discovery of the effect of monoamine oxidase inhibitors came about by accident. Iproniazid, originally developed for tuberculosis, was found to have psychoactive properties while being used for its intended purpose. This led to its development as the first MAOI and antidepressant.

Mechanism of action

MAOIs act by inhibiting the activity of monoamine oxidase, thus preventing the breakdown of monoamine neurotransmitters and thereby increasing their availability. There are two isoforms of monoamine oxidase, MAO-A and MAO-B. MAO-A preferentially deaminates serotonin, melatonin, epinephrine, and norepinephrine. MAO-B preferentially deaminates phenethylamine and certain other trace amines; in contrast, MAO-A preferentially deaminates other trace amines, like tyramine, whereas dopamine is equally deaminated by both types.

Side effects

The side effects of MAOIs include a hypertensive crisis, which can be potentially fatal, if foods containing tyramine are consumed. Other side effects include dry mouth, nausea, diarrhea or constipation, low blood pressure, and insomnia.

See also

• Antidepressant
• Phenethylamine
• Tyramine

References

Monoamine oxidase inhibitors Resources
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