MAOI

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Monoamine oxidase inhibitors (MAOIs) are chemicals which inhibit the activity of the monoamine oxidase enzyme family. They have a long history of use as medications prescribed for the treatment of depression. They are particularly effective in treating atypical depression. They are also used in the treatment of Parkinson's Disease and several other disorders.

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, adrenaline, and noradrenaline. MAO-B preferentially deaminates phenylethylamine and trace amines. Dopamine is equally deaminated by both types.

Reversibility

The early MAOIs inhibited monoamine oxidase irreversibly. When they react with monoamine oxidase, they permanently deactivate it, and the enzyme cannot function until it has been replaced by the body, which can take about two weeks. A few newer MAOIs (known as RIMAs are reversible, meaning that they are able to detach from the enzyme to facilitate usual catabolism of the substrate.

Interactions

The MAOIs are infamous for their numerous drug interactions, including the following kinds of substances:

• Substances that are metabolized by monoamine oxidase, as they can be boosted by up to several-fold.
• Substances that increase serotonin, noradrenaline, or dopamine activity as too much of any of these neurochemicals can result in severe acute consequences including serotonin syndrome, hypertensive crisis, and psychosis, respectively. Such substances include phenethylamines, amphetamines, tryptamines, lysergamides, and monoamine reuptake inhibitors.
• Other Monoamine Oxidase Inhibitors.

See also

• RIMA

References

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