Mirtazapine, originally branded Remeron, is an atypical antidepressant with noradrenergic and specific serotonergic activity. It blocks the ?2 adrenergic auto- and heteroreceptors (enhancing norepinephrine and serotonin release), and selectively antagonizes the 5-HT2 serotonin receptors in the central and peripheral nervous system. It also enhances serotonin neurotransmission at the 5-HT1 receptor and blocks the histaminergic (H1). Mirtazapine is not a serotonin or norepinephrine reuptake inhibitor but increases serotonin and norepinephrine action by other mechanisms.
Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA) developed by Organon International in the Netherlands, and introduced in the United States in 1996, and is used primarily in the treatment of depression. It is also commonly used as an anxiolytic, hypnotic, antiemetic and appetite stimulant. In structure, mirtazapine can also be classified as a tetracyclic antidepressant (TeCA) and is the 6-aza analogue of mianserin.
Its patent expired in 2004, so generic versions are available.
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Medical uses
Approved and off-label
Mirtazapine's primary use is the treatment of major depressive disorder and other mood disorders.
However, it has also been found useful in alleviating the following conditions and is sometimes prescribed off-label for their treatment:
Efficacy and tolerability
A 2011 Cochrane review that compared mirtazapine to other antidepressants, found that while it appears to have a faster onset in people for whom it works (measured at 2 weeks), it is about the same as other antidepressants at 6 weeks.
A 2012 review focused on antidepressants and sleep found that in many people with sleep disorders caused by depression, mirtazapine reduces the time it takes to fall asleep and increases the quality of sleep, but that in some people it can disturb sleep, causing restless leg syndrome in 8 to 28% of people, and in rare cases causes REM sleep behavior disorder.
In 2010 NICE published a guideline for treating depression that included a review of antidepressants. It recommended generic SSRIs as first line choices, as they are "are equally effective as other antidepressants and have a favourable risk-benefit ratio." With respect to mirtazapine, it found: "There is no difference between mirtazapine and other antidepressants on any efficacy measure, although in terms of achieving remission mirtazapine appears to have a statistical though not clinical advantage. In addition, mirtazapine has a statistical advantage over SSRIs in terms of reducing symptoms of depression, but the difference is not clinically important. However, there is strong evidence that patients taking mirtazapine are less likely to leave treatment early because of side effects, although this is not the case for patients reporting side effects or leaving treatment early for any reason."
In general, all antidepressants, including mirtazapine, require at least a week for their therapeutic benefits on depressive and anxious symptoms to become apparent.
Adverse reactions
A 2011 Cochrane review found that compared with other antidepressants, it is more likely to cause weight gain and sleepiness, but it is less likely to cause tremor than tricyclic antidepressants, and less likely to cause nausea and sexual dysfunction than SSRIs.
Very common (>=10% incidence) adverse effects include constipation, dry mouth, sleepiness, increased appetite, and weight gain.
Common (1%<= incidence <10%) adverse effects include weakness, confusion, dizziness, peripheral edema, and negative lab results like elevated transaminases, elevated serum triglycerides, and elevated total cholesterol.
Mirtazapine is not considered to have a risk of many of the side effects often associated with other antidepressants like the SSRIs, and may actually improve certain ones when taken in conjunction with them. (Those adverse effects include decreased appetite, weight loss, insomnia, nausea and vomiting, diarrhoea, urinary retention, increased body temperature, excessive sweating, pupil dilation and sexual dysfunction.)
In general, some antidepressants, especially SSRIs, can paradoxically exacerbate some peoples' depression or anxiety or cause suicidal ideation. Despite its sedating action, mirtazapine is also believed to be capable of this, so in the United States and certain other countries, it carries a black box label warning of these potential effects.
A case report published in 2000 noted an instance in which mirtazapine counteracted the action of clonidine, causing a dangerous rise in blood pressure.
Discontinuation
Mirtazapine and other antidepressants may cause a discontinuation syndrome upon cessation. A gradual and slow reduction in dose is recommended to minimize discontinuation symptoms. Effects of sudden cessation of treatment with mirtazapine may include depression, anxiety, panic attacks, vertigo, restlessness, irritability, decreased appetite, insomnia, diarrhea, nausea, vomiting, flu-like symptoms such as allergies and pruritus, headaches and sometimes hypomania or mania.
Overdose
Mirtazapine is considered to be relatively safe in the event of an overdose, although it is considered slightly more toxic in overdose than most of the SSRIs (except citalopram). Unlike the TCAs, mirtazapine showed no significant cardiovascular adverse effects at 7 to 22 times the maximum recommended dose. Case reports of overdose with as much as 30 to 50 times the standard dose described the drug as relatively nontoxic, compared to TCAs.
Twelve reported fatalities have been attributed to mirtazapine overdose. The fatal toxicity index (deaths per million prescriptions) for mirtazapine is 3.1 (95% CI: 0.1 to 17.2). This is similar to that observed with SSRIs.
Interactions
Concurrent use with inhibitors or inducers of the cytochrome (CYP) P450 isoenzymes CYP1A2, CYP2D6, and/or CYP3A4 can result in altered concentrations of mirtazapine, as these are the main enzymes responsible for its metabolism. As examples, fluoxetine and paroxetine, inhibitors of these enzymes, are known to modestly increase mirtazapine levels, while carbamazepine, an inducer, considerably decreases them.
According to information from the manufacturers, mirtazapine should not be started within two weeks of any monoamine oxidase inhibitor (MAOI) usage; likewise, MAOIs should not be administered within two weeks of discontinuing mirtazapine. However, a single study regarding the combination reported it does not result in any incidence of serotonin-related toxicity. In addition, a case report claimed that mirtazapine can actually be used to treat serotonin syndrome. Mirtazapine in combination with an SSRI, SNRI, or TCA as an augmentation strategy is considered to be relatively safe and is often employed therapeutically, with a combination of venlafaxine and mirtazapine, sometimes referred to as "California rocket fuel".
Mirtazapine's combination with an Serotonin-norepinephrine reuptake inhibitor is especially considered to have synergistic effect on serotonin and Norepinephrine, and like Venlafaxine, its combination with Duloxetine/Cymbalta is sometimes referred to as "Limerick Rocket Fuel".
Another case report described mirtazapine as inducing hypertension in a clonidine-treated patient, likely due to occupancy of ?2 autoreceptors by mirtazapine limiting the efficacy of concurrent clonidine therapy.
Liver and moderate renal impairment have been reported to decrease the oral clearance of mirtazapine by about 30%; severe renal impairment decreases it by 50%.
Pharmacology
Binding profile
Mirtazapine is an antagonist/inverse agonist at the following receptors:
All affinities listed were assayed using human materials except those for ?1 adrenergic and mACh that are for rat tissues, due to human values being unavailable.
Mirtazapine has recently been found to act as a weak (EC50 7.2 ?M) ?-opioid receptor partial agonist.
Correspondence to clinical effects
Antagonization of the ?2 adrenergic receptors, which function largely as autoreceptors and heteroreceptors, enhances adrenergic and serotonergic neurotransmission, the notable ones being central 5-HT1A receptor mediated transmission in the dorsal raphe nucleus and hippocampus; hence, mirtazapine's classification as a NaSSA. Indirect ?1 adrenoceptor-mediated enhancement of 5-HT cell firing and direct blockade of inhibitory ?2 heteroreceptors located on 5-HT terminals are held responsible for the increase in extracellular 5-HT. Because of this, mirtazapine has been said to be a functional "indirect agonist" of the 5-HT1A receptor. Increased activation of the central 5-HT1A receptor is thought to be a major mediator of efficacy of most antidepressant drugs. Unlike most conventional antidepressants, however, at clinically used doses mirtazapine has no appreciable affinity for the serotonin, norepinephrine, or dopamine transporters and thus lacks any significant effects as a reuptake inhibitor of these neurotransmitters, nor does it have any significant inhibitory effects on monoamine oxidase.
Antagonism of the 5-HT2 subfamily of receptors and inverse agonism of the 5-HT2C receptor appears to be in part responsible for mirtazapine's efficacy in the treatment of depressive states. The 5-HT2C receptor is known to inhibit the release of the neurotransmitters dopamine and norepinephrine in various parts of the brains of rodents, notably in reward pathways such as the ventral tegmental area. Accordingly, it was shown that by blocking the ?2 adrenergic receptors and 5-HT2C receptors mirtazapine disinhibited dopamine and norepinephrine activity in these areas in rats. In addition, mirtazapine's antagonism of 5-HT2A receptors has beneficial effects on anxiety, sleep and appetite, as well as sexual function regarding the latter receptor. The newest research however has shown that mirtazapine is actually an inverse agonist of the 5-HT2C receptor. 5-HT2C inverse agonists have been shown to inhibit mesoaccumbens dopamine outflow attenuating the rewarding properties of various substances like morphine. This inhibition of dopamine may be stronger than thought as substances with 5-HT2C inverse agonist properties may have more activity to regulate dopamine neurotransmission than ones with competitive antagonism. With its newly understood properties of 5-HT2C inverse agonism, it is being investigated and shown to lower drug seeking behaviour, conditioned place preference and the rewarding effects of substances such as methamphetamine in various human and animal studies. It is also being investigated to help in substance abuse disorders with withdrawal effects and remission rates. but some studies have shown mixed benefit.
Antagonism of the 5-HT3 receptor, an action mirtazapine shares with the approved antiemetic ondansetron, significantly improves pre-existing symptoms of nausea, vomiting, diarrhea, and irritable bowel syndrome in afflicted individuals. Mirtazapine may be used as an inexpensive antiemetic alternative to ondansetron. Blockade of the 5-HT3 receptors has also shown to improve anxiety and to be effective in the treatment of drug addiction in several studies. In conjunction with substance abuse counseling, mirtazapine has been investigated for the purpose of reducing methamphetamine use in dependent individuals with success. In contrast to mirtazapine, the SSRIs, SNRIs, MAOIs, and some TCAs increase the general activity of the 5-HT2A, 5-HT2C, and 5-HT3 receptors leading to a host of negative changes and side effects, the most prominent of which including anorexia, insomnia, sexual dysfunction (loss of libido and anorgasmia), nausea, and diarrhea, among others. As a result, it is often combined with these drugs to reduce their side-effect profile and to produce a stronger antidepressant effect.
Mirtazapine is a very strong H1 receptor inverse agonist and, as a result, it can cause powerful sedative and hypnotic effects. After a short period of chronic treatment, however, the H1 receptor tends to desensitize and the antihistamine effects become more tolerable. Many patients may also dose at night to avoid the effects, and this appears to be an effective strategy for combating them. Blockade of the H1 receptor may improve pre-existing allergies, pruritus, nausea, and insomnia in afflicted individuals. It may also contribute to weight gain, however. In contrast to the H1 receptor, mirtazapine has very low affinity for the mACh receptors, although anticholinergic side effects like dry mouth, constipation, and mydriasis are still commonly seen in clinical practise.
Like many other antidepressants, mirtazapine has been found to have antinociceptive properties in mice. However, unlike most other antidepressants, though similarly to venlafaxine, these effects appear to be mostly mediated through downstream modulation of ? opioid and ?3 opioid receptors, and this opioid receptor activity may account for some of its anti-depressant activity.
Pharmacokinetics
The (S)-(+)-enantiomer has a plasma half-life of 9.9±3 hours and the (R)-(-)-enantiomer has a plasma half-life of 18±2.5 hours.
It is found mostly bound to plasma protein. The overall elimination half-life is 20-40 hours. It is metabolized primarily in the liver by demethylation and hydroxylation. About 75% is eliminated in feces and 25% in urine.
Chemistry
Mirtazapine is a tetracyclic piperazinoazepine; mianserin was developed by the same team of organic chemists and mirtazapine differs from it via addition of a nitrogen atom in one of the rings.
Mirtazapine is a racemic mixture of enantiomers. The (S)-(+)-enantiomer is known as esmirtazapine.
A four-step chemical synthesis of mirtazapine has been published.
History
Mirtazapine was first synthesized at Organon and published in 1989, was first approved for use in major depressive disorder in the Netherlands in 1994, and was introduced in the United States in 1996 under the brand name Remeron.
Brands
Mirtazapine is marketed under many brand names worldwide, including Adco-Mirteron, Afloyan, Amirel, Arintapin Smelt, Avanza, Azapin, Beron, Bilanz, Calixta, Ciblex, Combar, Comenter, Depreram, Divaril, Esprital, Maz, Menelat, Mepirzapine, Merdaten, Meronin, Mi Er Ning, Milivin, Minelza, Minivane, Mirastad, Mirazep, Miro, Miron, Mirrador, Mirt, Mirta, Mirtabene, Mirtadepi, Mirtagamma, Mirtagen, Mirtalan, Mirtamor, Mirtamylan, Mirtan, Mirtaneo, Mirtapax, Mirtapil, Mirtapine, Mirtaron, Mirtastad, Mirtax, Mirtaz, Mirtazap, Mirtazapin, Mirtazapina, Mirtazapine, Mirtazapinum, Mirtazelon, Mirtazon, Mirtazonal, Mirtel, Mirtimash, Mirtin, Mirtine, Mirzapine, Mirzaten, Mirzaten, Mirzest, Mitaprex, Mitaxind, Mitocent, Mitrazin, Mizapin, Motofen, Mytra, Norset, Noxibel, Pharmataz, Promyrtil, Ramure, Redepra, Reflex, Remergil, Remergon, Remeron, Remirta, Rexer, Saxib, Sinmaron, Smilon, Tazepin, Tazimed, Tetrazic, Tifona, U-Mirtaron, U-zepine, Valdren, Vastat, Velorin, Yarocen, Zania, Zapex, Zestat, Zismirt, Zispin, Zuleptan, and Zulin.
Research
The use of mirtazapine has been explored in several additional conditions:
- Sleep apnea/hypopnea
- Inappropriate sexual behaviour and other secondary symptoms of autistic spectrum conditions and other pervasive developmental disorders
- Antipsychotic-induced akathisia.
- Drug withdrawal, dependence and detoxification
- Negative, depressive and cognitive symptoms of schizophrenia (as an adjunct)
- A case report has been published in which mirtazapine reduced visual hallucinations in a patient with Parkinson's disease psychosis (PDP). This is in alignment with recent findings that inverse agonists at the 5-HT2A receptors are efficacious in attenuating the symptoms of Parkinson's disease psychosis. As is supported by the common practice of prescribing low-dose quetiapine and clozapine for PDP-doses too low to antagonise the D2 receptor, but sufficiently high doses to inversely agonise the 5-HT2A receptors.
- Eight case reports have been reported in five papers on the use of mirtazapine in the treatment of hives as of 2017.
Veterinary use
Mirtazapine is sometimes prescribed as an appetite stimulant for cats or dogs experiencing anorexia due to medical conditions such as chronic kidney disease. It is especially useful for treating combined poor appetite and nausea in cats and dogs.
Source of the article : Wikipedia
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