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14-September-2008 18:02:40 - Monoamine oxidase inhibitor April 2007 MAOI redirects here. For the Easter Island statues, see Moai. Monoamine oxidase Monoamine oxidase Monoamine oxidase inhibitors MAOIs are a class of powerful antidepressant drugs prescribed for the treatment of depression. They are particularly effective in treating atypical depression, and have also shown efficacy in smoking cessation. Due to potentially lethal dietary and drug interactions, MAOIs had been reserved as a last line of defense, used only when other classes of antidepressant drugs for example selective serotonin reuptake inhibitors and tricyclic antidepressants have been tried unsuccessfully. Recently, however, a patch form of the drug selegiline, called Emsam, was developed. It was approved for use by the FDA on February 28, 2006.1 When applied transdermally the drug does not enter the gastro-intestinal system as it does when taken orally, thereby decreasing the dangers of dietary interactions associated with MAOI pills. Contents 1 Uses 1.1 Therapeutic use 2 Mode of action 2.1 Reversibility 2.2 Selectivity 3 Dangers 3.1 Drug interactions 4 List of MAOIs 4.1 Reversible type B selective MAOIs 4.1.1 Research prototypes 5 References Uses Therapeutic use In the past they were prescribed for those resistant to tricyclic antidepressant therapy, but newer MAOIs are now sometimes used as first-line therapy. They are also used for treating agoraphobia or social anxiety. Currently, the availability of selegiline and moclobemide provides a safer alternative, although these substances are not always as effective as their predecessors. MAO inhibitors can also be used in the treatment of Parkinson's disease by affecting dopaminergic neurons, as well as providing an alternative for migraine prophylaxis. Mode of action MAOIs act by inhibiting the activity of monoamine oxidase preventing the breakdown of monoamine neurotransmitters, which increases 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 phenylethylamine and trace amines. Dopamine is equally deaminated by both types. Many formulations have forms of fluoride attached to assist in permeating the blood-brain barrier, which is suspected as a factor in pineal gland effects. 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, notably moclobemide, are reversible, meaning that they are able to detach from the enzyme to facilitate usual catabolism of the substrate. The level of inhibition in this way is governed by the respective concentrations of the substrate and the MAOI. Harmaline found in Peganum harmala is a reversible inhibitor of MAO-A RIMA.2 Selectivity In addition to reversibility, MAOIs differ by their selectivity of the MAO receptor. Some MAOIs inhibit both MAO-A and MAO-B equally, other MAOIs have been developed that target one over the other. MAO-A inhibition reduces the breakdown of primarily serotonin, epinephrine, and norepinephrine and thus has a higher risk of serotonin syndrome and/or a hypertensive crisis. Tyramine is broken down by MAO-A, therefore inhibiting its action may result in excessive build up of it, so diet must be monitored for tyramine intake. MAO-B inhibition reduces the breakdown mainly of dopamine and phenethylamine so there are no dietary restrictions associated with this. Two such drugs, selegiline and rasagiline have been approved by the FDA without dietary restrictions, except in high dosage treatment where they lose their selectivity.13 Dangers When ingested orally, MAOIs inhibit the catabolism of dietary amines. Sufficient intestinal MAO-A inhibition can lead to hypertensive crisis, when foods containing tyramine are consumed so-called cheese syndrome, or hyperserotonemia if foods containing tryptophan are consumed. The amount required to cause a reaction exhibits great individual variation and depends on the degree of inhibition, which in turn depends on dosage and selectivity. The exact mechanism by which tyramine causes a hypertensive reaction is not well understood, but it is assumed that tyramine displaces norepinephrine from the storage vesicles.4 This may trigger a cascade in which excessive amounts of norepinephrine can lead to a hypertensive crisis. Another theory suggests that proliferation and accumulation of catecholamines causes hypertensive crises. Tyrosine is the precursor to catecholamines, not tyramine. Tyramine is a breakdown product of tyrosine. In the gut and during fermentation tyrosine, an amino acid, is decarboxylated to tyramine. Ordinarily, tyramine is deaminated in the liver to an inactive metabolite, but when the hepatic MAO primarily MAO-A is inhibited, the first-pass clearance of tyramine is blocked and circulating tyramine levels can climb. Elevated tyramine competes with tyrosine for transport across the blood-brain barrier via aromatic amino acid transport where it can then enter adrenergic nerve terminals. Once in the cytoplasmic space, tyramine will be transported via the vesicular monoamine transporter VMAT into synaptic vesicles thereby displacing norepinephrine. The mass transfer of norepinephrine from its vesicular storage space into the extracellular space via mass action can precipitate the hypertensive crisis. Hypertensive crises can sometimes result in stroke or cardiac arrhythmia if not treated. This risk is generally not present with RIMAs. Both kinds of intestinal MAO inhbition can cause hyperpyrexia, nausea and psychosis if foods high in levodopa are consumed. Chronic use of MAOIs may provide some antidepressant effects that are thought to be mediated by metabolism of tyramine to octopamine, a reaction catalyzed by phenyl-N-methyl transferase that normally converts dopamine to norepinephrine. Octopamine may then act as a false transmitter in that it is stored and released like the endogenous transmitter norepinephrine. However, it is a poor agonist of postsynaptic adrenoceptors while retaining agonist activity at presynaptic autoreceptors. This action reduces adrenergic transmission by diminishing postsynaptic receptor activation and by a presynaptic autoinhibitory effect. Finally, octopamine may serve as an agonist at a novel trace amine receptor expressed at low levels throughout the brain. Examples of foods and drinks with potentially high levels of tyramine include fermented substances, such as Chianti and other aged wines, and aged cheeses. Liver is also a well-known source. See a list of foods containing tyramine. Examples of levodopa-containing foods include broad beans also known in the United States as fava beans. These diet restrictions are not necessary for those taking selective MAO-B inhibitors. It deserves separate mention that some meat extracts and yeast extracts Bovril, Marmite, Vegemite contain extremely high levels of tyramine, and should not be used with these medications. When MAOIs were first introduced, these risks were not known, and over the following four decades, fewer than 100 people have died from hypertensive crisis.citation needed Presumably due to the sudden onset and violent appearance of the reaction, MAOIs gained a reputation for being so dangerous that, for a while, they were taken off the market in America entirely. It is now known that, used as directed under the care of a qualified psychiatrist, this class of drugs remains a safe alternative for intermediate- to long-term use. The most significant risk associated with the use of MAOIs, is the potential for interactions with over-the-counter and prescription medicines, illicit drugs and certain supplements e.g. St. John's Wort. It is vital that a doctor supervise such combinations to avoid adverse reactions. For this reason, many users carry an MAOI-card, which lets emergency medical personnel know what drugs to avoid. E.g. adrenaline dosage should be reduced by 75%, and duration is extended MAOIs should not be combined with other psychoactive substances antidepressants, illicit drugs, painkillers, stimulants, etc. except under expert care. Certain combinations can cause lethal reactions, common examples including SSRIs, tricyclics, MDMA, meperidine, tramadol, and dextromethorphan. Agents with actions on epinephrine, norepinephrine or dopamine must be administered at much lower doses due to potentiation and prolonged effect. Purely opiate-acting analgesics, such as morphine and buprenorphine may be used safely with MAOIs, but may require a dosage adjustment. Drug interactions This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. December 2007 Sympathomimetics e.g. pseudoephedrine in cold remedies Risk of hypertensive crisis Reserpine, guanethidine, tricyclic antidepressants Excitement Increase in blood pressure and body temperature Levodopa L-DOPA Excitement Hypertension Anticholinergics Henbane, Datura Risk of hallucination Antihistamines, barbiturates, ethanol, opioids Action of these drugs prolonged - risk of respiratory depression Pethidine Demerol Risk of high fever, sweating, excitement, delirium, convulsions, respiratory depression MAOIs retard metabolism of pethidine, but not its demethylation, therefore excess norpethidine is formed. Methylenedioxymethamphetamine MDMA, Ecstasy Risk of hypertensive crisis Serotonin syndrome Dextromethorphan DXM, cough-syrup Serotonin syndrome Imitrex/Sumatriptan, Migraine Medicine Dimethyltryptamine Increases oral activity Action of this drug is greatly prolonged Dimethyltryptamine is often intentionally combined with MAOIs, and can be found in the psychoactive decoction ayahuasca Dimethyltryptamine is extremely low in toxicity and the interaction is only as dangerous as the MAOI by itself. List of MAOIs Monoamine oxidase inhibitors include: Isocarboxazid Marplan Moclobemide Aurorix, Manerix, Moclodura Phenelzine Nardil Tranylcypromine Parnate contents 5 mg, Jatrosom contents 10 mg Selegiline Selegiline, Eldepryl, and Emsam Rasagiline Azilect Nialamide Iproniazid Marsilid, Iprozid, Ipronid, Rivivol, Propilniazida Iproclozide Toloxatone Linezolid Zyvox, Zyvoxid, an antibiotic of the oxazolidinone family, is a reversible, nonselective MAOI which has been known to induce serotonin syndrome post SSRI ingestion. Zyvox requires the same dietary precautions as other MAOI's Many tryptamines have MAOI properties. Harmine present in Harmal, Banisteriopsis caapi, and tobacco is a powerful MAOI, which is often used as one of the ingredients of ayahuasca. Certain synthetic tryptamines such as AMT, 5-MeO-DMT or 5-MeO-AMT produce only minor MAO inhibition. The phenethylamine derivatives substituted with a sulfur at the 4-position, such as 2C-T-7 are quite potent MAO-A inhibitors,5 which makes them potentially dangerous when taken in large doses, or when combined with stimulants such as ephedrine or MDMA. Some deaths have occurred from such combinations. Dienolide kavapyrone desmethoxyyangonin MAOI-B6 Dextroamphetamine 2 Methylene blue methylene blue Reversible type B selective MAOIs Research prototypes Safinamide,7 in phase III for Parkinson's disease8 Certain coumarines umbelliferones910 including geiparvarin11 5H-Indeno1,2-cpyridazin-5-ones121314 References ^ a b U.S. Food and Drug Administration 2006-02-28. FDA Approves Emsam Selegiline as First Drug Patch for Depression.. Press release. Retrieved on 2007-12-02. ^ Edward J. Massaro, Handbook of Neurotoxicology ^ BLTC Research 1 2006. Rasagiline: a neuroprotective smart drug?. The Good Drug Guide. Retrieved on 2007-12-02. At dosages above around 2 mg per day, rasagiline loses its selectivity for MAO type B and also inhibits MAO type A. An MAO-B selective regimen does not cause significant tyramine potentiation, the dreaded 'cheese effect' common to users of older unselective and irreversible MAOIs who eat tyramine-rich foods. Thus low-dosage rasagiline demands no special dietary restrictions. ^ Jacob, Giris; Gamboa, Alfredo; Diedrich, André; Shibao, Cyndya; Robertson, David; Biaggioni, Italo August 2005. Tyramine-Induced Vasodilation Mediated by Dopamine Contamination: A Paradox Resolved. Hypertension 46 2: 358. Lippincott Williams Wilkins. doi:10.1161/01.HYP.0000172353.62657.8b. PMID 15967868. Retrieved on 2007-12-02. Tyramine displaces norepinephrine from neuronal vesicles into the axoplasm, and it is likely that some of it is converted to DHPG, and only a portion reaches the circulation. ^ PMID 17521909 2007: Human and rat monoamine oxidase-A are differentially inhibited by S-4-alkylthioamphetamine derivatives: insights from molecular modeling studies. ^ PMID 9832350 1998: Inhibition of platelet MAO-B by kava pyrone-enriched extract from Piper methysticum Forster kava-kava. ^ PMID 17824599 2007: Solid-phase synthesis and insights into structure-activity relationships of safinamide analogues as potent and selective inhibitors of type B monoamine oxidase. ^ PMID 17199024 2007 ^ PMID 17915852 2007: Structures of human monoamine oxidase B complexes with selective noncovalent inhibitors: safinamide and coumarin analogs. ^ PMID 16884303 2006: Structural insights into monoamine oxidase inhibitory potency and selectivity of 7-substituted coumarins from ligand- and target-based approaches. ^ PMID 12443774 2002: Natural and synthetic geiparvarins are strong and selective MAO-B inhibitors. Synthesis and SAR studies ^ PMID 17910428 2007: Synthesis and Monoamine Oxidase Inhibitory Activity of New Pyridazine-, Pyrimidine- and 1,2,4-Triazine-Containing Tricyclic Derivatives ^ PMID 12467619 2003: Rational approaches towards reversible inhibition of type B monoamine oxidase. Design and evaluation of a novel 5H-Indeno1,2-cpyridazin-5-one derivative. ^ PMID 17034132 2006: Impact of Species-Dependent Differences on Screening, Design, and Development of MAO B Inhibitors v d e Receptor agonists, antagonists, and reuptake inhibitors BA/M 5-HT serotonin receptor Serotonin receptor agonist 5-HT4 · Serotonin antagonist 5-HT3 · Serotonin uptake inhibitor SSRI Dopamine receptor Dopamine agonist · Dopamine antagonist · Dopamine reuptake inhibitor Adrenergic receptor Adrenergic agonist Alpha, Beta 1/2 · Adrenergic antagonist Alpha 1/2, Beta · Adrenergic uptake inhibitor Histamine receptor Histamine agonist · Histamine antagonist H1, H2, H3 AA GABA receptor GABA agonist · GABA antagonist Glutamate receptor NMDA receptor NMDA receptor antagonist · AMPA receptor Ampakine · Excitatory amino acid agonist · Excitatory amino acid antagonist ANS Acetylcholine receptor Cholinergic Muscarinic, Nicotinic · Anticholinergic Muscarinic, Nicotinic/Ganglionic blocker/Neuromuscular-blocking drugs · Acetylcholinesterase inhibitor Adrenergic receptor SANS only-see above for details PANS Parasympathomimetic Cholinergic, Acetylcholinesterase inhibitor · Parasympatholytic Anticholinergic, Ganglionic blocker SANS Sympathomimetic Adrenergic agonist, Monoamine oxidase inhibitor · Sympatholytic Adrenergic antagonist, Alpha blocker, Ganglionic blocker v d e Pharmacology: enzyme inhibition Class Competitive inhibition - Uncompetitive inhibition - Non-competitive inhibition - Suicide inhibition - Mixed inhibition Substrate Oxidoreductase EC 1: Aromatase inhibitors - Lipoxygenase inhibitor - Monoamine oxidase inhibitors - COX-2 inhibitor Transferase EC 2: Integrase inhibitor - Protein kinase inhibitors - Reverse transcriptase inhibitors - COMT inhibitors Hydrolase EC 3: Acetylcholinesterase inhibitors - Phosphodiesterase inhibitors - Protease inhibitors ACE inhibitor, Trypsin inhibitor - Histone deacetylase inhibitor Lyase EC 4: Carbonic anhydrase inhibitors v d e Psychoanaleptics: antidepressants N06A MAOIs Clorgiline Iproclozide Iproniazid Isocarboxazid Minaprine Nialamide Pargyline Phenelzine Toloxatone Tranylcypromine MAOB: Rasagiline Selegiline RIMAs: Befloxatone Brofaromine Cimoxatone Beta-carbolines Harmaline Moclobemide RIs S RI SS RI Alaproclate, Citalopram, Dapoxetine, Escitalopram, Femoxetine, Fluoxetine, Fluvoxamine, Paroxetine, Sertraline, Vilazodone, Zimelidine TCAs/Tetras Cianopramine, Clomipramine, Nefazodone, Trazodone N RI / A RI Atomoxetine Ciclazindol Maprotiline Nisoxetine Oxaprotiline Reboxetine Talopram Viloxazine TCAs/Tetras Amitriptyline, Amoxapine, Butriptyline, Desipramine/Lofepramine, Dibenzepin, Dosulepin, Doxepin, Imipramine, Iprindole, Melitracen, Nitroxazepine, Nortriptyline, Protriptyline, Trimipramine D RI Medifoxamine Phenmetrazine Vanoxerine TCAs Amineptine SN RI Bicifadine Clovoxamine Desvenlafaxine Duloxetine Milnacipran Nefazodone Venlafaxine ND RI Bupropion Nomifensine SND RI Brasofensine Diclofensine Tesofensine SSREs Tianeptine AAs Tetras Mianserin, Mirtazapine v d e Anti-parkinson drugs: dopaminergic agents N04B Dopa and derivatives Droxidopa Levodopa Melevodopa Etilevodopa Adamantane derivatives Amantadine Dopamine agonists A-412,997 Aplindore Apomorphine Bromocriptine Cabergoline Dihydrexidine Dihydroergocryptine mesylate Fenoldopam Lisuride Pergolide Piribedil Pramipexole Propylnorapomorphine Quinpirole Ropinirole Rotigotine SKF 38393 SKF 82958 MAOIs B Selegiline Rasagiline COMT inhibitors Entacapone Tolcapone Other Budipine dopa decarboxylase inhibitor Carbidopa Retrieved from http://en..org/wiki/Monoamine_oxidase_inhibitor Categories: Antidepressants | Monoamine oxidase inhibitorsHidden categories: Articles needing additional references from April 2007 | All articles with statements | Articles with statements since December 2007 | Articles needing additional references from December 2007 Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Deutsch Français עברית Nederlands 日本語 Polski Português Suomi This page was last modified on 10 September 2008, at 02:4
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