Monoamine oxidase inhibitor

**Monoamine oxidase inhibitors** (MAOIs) and **reversible monoamine oxidase inhibitors** (RIMAs) are a type of antidepressant drugs given for the treatment of depression. They are good at treating atypical depression, Parkinson's disease, anxiety disorders, social phobia and have also shown to help people with stopping smoking tobacco.

As MAOIs drugs can be fatal if someone takes too much, they are usually only ever given when other antidepressant drugs have failed. Some newer drugs such as selegiline and moclobemide have proven to be safer than the older MAOIs and are prescribed by physicians in the first instance.

## Uses

MAOIs and RIMAs are used to provide a second line of treatment for certain psychiatric illnesses, most commonly types of hard to treat depression with not normal symptoms and anxiety disorders (with or without panic attacks). They may also be used for social phobia. MAO-B inhibitors are used to treat Parkinson's disease. Certain MAOIs have been shown to help people to stop smoking tobacco.

## How they work

Monoamine oxidase inhibitors work by stopping the action of an enzyme called monoamine oxidase. This enzyme breaks down a group of brain signalling chemicals called the monoamine neurotransmitters. There are two types of the enzyme, MAO-A and MAO-B. Each type breaks apart different chemicals in the group. MAO-A breaks down melatonin, serotonin, epinephrine and norepinephrine. MAO-B breaks down phenylethylamine and the trace amines. These chemicals (neurotransmitters) are used in the brain for signalling purposes. Dopamine, for example, is a chemical that affects motivation and pleasure. Effectively, they work on balancing the brain's chemistry.

## Side effects

Like all drugs, MAOIs and RIMAs can have effects that are not intended and are not part of the treatment that the drugs provide. In this class of drug, these include a risk of a hypertensive crisis. This can be caused by high levels of tyramine; such as by eating cheese (except cream or cottage cheese, meat extracts such as Bovril, yeast extract, stock cubes, fermented soya bean products, alcohol (especially fortified wine (port, sherry), beer and chainti wine. Also preserved fish, preserved poultry, offal, avocado, banana skins, broad bean pods and pickled or smoked herring must be avoided. Certain medications can also cause a hypertensive crisis with MAOIs and RIMAs, such as; amphetamine, fenfluramine, ephedrine, phenlyephrine, phenylpropanolamine, nasal decongestants, L-dopa, pethidine and tricyclic antidepressants. Use of a RIMA rather than a MAOI can reduce these side-effects, however tyramine rich foods should still be avoided.

### Marketed MAOIs

- Nonselective MAO-A/MAO-B inhibitors
    - Hydrazine (antidepressant)
        - Isocarboxazid (Marplan)
        - Hydracarbazine
        - Phenelzine (Nardil, Nardelzine)
    - Non-hydrazines
        - Tranylcypromine (Parnate, Jatrosom)
- Selective MAO-A inhibitors
    - Bifemelane (Alnert, Celeport) (available in Japan)
    - Methylene blue (Urelene blue, Provayblue, Proveblue)
    - Moclobemide (Aurorix, Manerix, Moclamine)
    - Pirlindole (Pirazidol) (available in Russia)
- Selective MAO-B inhibitors
    - Rasagiline (Azilect)
    - Selegiline (Deprenyl, Eldepryl, Emsam, Zelapar)
    - Safinamide (Xadago)

Linezolid is an antibiotic drug with weak, reversible MAO-inhibiting activity.

The antibiotic furazolidone also has MAO-inhibiting activity

Methylene blue (methylthioninium chloride), the antidote indicated for drug-induced methemoglobinemia on the World Health Organization's List of Essential Medicines, among a plethora of other off-label uses, is a highly potent, reversible MAO inhibitor.

The Food and Drug Administration (FDA) has approved these <abbr>MAOIs</abbr> to treat depression:

- Isocarboxazid (Marplan)
- Phenelzine (Nardil)
- Selegiline (Emsam)
- Tranylcypromine (Parnate)

### MAOIs that have been withdrawn from the market

- Nonselective MAO-A/MAO-B inhibitors
    - Hydrazines
        - Benmoxin (Nerusil, Neuralex)
        - Iproclozide (Sursum)
        - Iproniazid (Marsilid, Iprozid, Ipronid, Rivivol, Propilniazida)
        - Mebanazine (Actomol)
        - Nialamide (Niamid)
        - Octamoxin (Ximaol, Nimaol)
        - Pheniprazine (Catron)
        - Phenoxypropazine (Drazine)
        - Pivalylbenzhydrazine (Tersavid)
        - Safrazine (Safra) (discontinued worldwide except for Japan)
    - Non-hydrazines
        - Caroxazone (Surodil, Timostenil)
- Selective MAO-A inhibitors
    - Minaprine (Cantor)
    - Toloxatone (Humoryl)

### List of RIMAs

**Marketed pharmaceuticals**

- Moclobemide (Aurorix, Manerix, Moclamine)

**Other pharmaceuticals**

- Brofaromine (Consonar)
- Caroxazone (Surodil, Timostenil)
- Eprobemide (Befol)
- Methylene blue
- Metralindole (Inkazan)
- Minaprine (Cantor)
- Pirlindole (Pirazidol)

**Naturally occurring RIMAs in plants**

Only reversible phytochemical MAOIs have been characterized.
- Harmaline
- Harmine
- Rosiridin (_in vitro_)

**Research compounds**

- Amiflamine (FLA-336)
- Befloxatone (MD-370,503)
- Cimoxatone (MD-780,515)
- Esuprone
- Sercloremine (CGP-4718-A)
- Tetrindole
- CX157 (TriRima)

## Related pages

- Psychiatry
- Mental illness
- Pharmacology
- Prescription drug

## Other websites

- Antidepressant, Monoamine Oxidase (Mao) Inhibitor (Oral Route) - Mayo Clinic