Tag: Antidepressant

What is Lubazodone?

Published on by Andrew MarshallLeave a comment

Introduction

Lubazodone (developmental code names YM-992, YM-35995) is an experimental antidepressant which was under development by Yamanouchi for the treatment for major depressive disorder in the late 1990s and early 2000s but was never marketed.

Outline

It acts as a serotonin reuptake inhibitor (Ki for SERTTooltip serotonin transporter = 21 nM) and 5-HT2A receptor antagonist (Ki = 86 nM), and hence has the profile of a serotonin antagonist and reuptake inhibitor (SARI). The drug has good selectivity against a range of other monoamine receptors, with its next highest affinities being for the α1-adrenergic receptor (Ki = 200 nM) and the 5-HT2C receptor (Ki = 680 nM).

Lubazodone is structurally related to trazodone and nefazodone, but is a stronger serotonin reuptake inhibitor and weaker as a 5-HT2A receptor antagonist in comparison to them and is more balanced in its actions as a SARI. It reached phase II clinical trials for depression, but development was discontinued in 2001 reportedly due to the “erosion of the SSRITooltip selective serotonin reuptake inhibitor market in the United States”.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Lubazodone >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is a Norepinephrine Transporter?

Published on by Andrew Marshall7 Comments

Introduction

The norepinephrine transporter (NET), also known as noradrenaline transporter (NAT), is a protein that in humans is encoded by the solute carrier family 6 member 2 (SLC6A2) gene.

NET is a monoamine transporter and is responsible for the sodium-chloride (Na+/Cl−)-dependent reuptake of extracellular norepinephrine (NE), which is also known as noradrenaline. NET can also reuptake extracellular dopamine (DA). The reuptake of these two neurotransmitters is essential in regulating concentrations in the synaptic cleft. NETs, along with the other monoamine transporters, are the targets of many antidepressants and recreational drugs. In addition, an overabundance of NET is associated with ADHD. There is evidence that single-nucleotide polymorphisms in the NET gene (SLC6A2) may be an underlying factor in some of these disorders.

Gene

The norepinephrine transporter gene, SLC6A2 is located on human chromosome 16 locus 16q12.2. This gene is encoded by 14 exons. Based on the nucleotide and amino acid sequence, the NET transporter consists of 617 amino acids with 12 membrane-spanning domains. The structural organisation of NET is highly homologous to other members of a sodium/chloride-dependent family of neurotransmitter transporters, including dopamine, epinephrine, serotonin and GABA transporters.

Single-Nucleotide Polymorphisms

A single-nucleotide polymorphism (SNP) is a genetic variation in which a genome sequence is altered by a single nucleotide (A, T, C or G). NET proteins with an altered amino acid sequence (more specifically, a missense mutation) could potentially be associated with various diseases that involve abnormally high or low plasma levels of norepinephrine due to altered NET function. NET SNPs and possible associations with various diseases are an area of focus for many research projects. There is evidence suggesting a relationship between NET SNPs and various disorders such as ADHD, psychiatric disorders, postural tachycardia and orthostatic intolerance. The SNPs rs3785143 and rs11568324 have been related to attention-deficit hyperactivity disorder. Thus far, however, the only confirmed direct association between a SNP and a clinical condition is that of the SNP, Ala457Pro, and orthostatic intolerance. Thirteen NET missense mutations have been discovered so far.

Genetic Variations

An epigenetic mechanism (hypermethylation of CpG islands in the NET gene promoter region) that results in reduced expression of the noradrenaline (norepinephrine) transporter and consequently a phenotype of impaired neuronal reuptake of norepinephrine has been implicated in both postural orthostatic tachycardia syndrome and panic disorder.

rs5569 is a variant of SLC6A2.

Structure

The norepinephrine transporter is composed of 12 transmembrane domains (TMDs). The intracellular portion contains an amino (-NH2) group and carboxyl (-COOH) group. In addition, there is a large extracellular loop located between TMD 3 and 4. The protein is composed of 617 amino acids.

Function

NET functions to transport synaptically released norepinephrine back into the presynaptic neuron. As much as 90% of the norepinephrine released will be taken back up in the cell by NET. NET functions by coupling the influx of sodium and chloride (Na+/Cl−) with the transport of norepinephrine. This occurs at a fixed ratio of 1:1:1. Both the NET and the dopamine transporter (DAT) can transport norepinephrine and dopamine. The reuptake of norepinephrine and dopamine is essential in regulating the concentration of monoamine neurotransmitters in the synaptic cleft. The transporter also helps maintain homeostatic balances of the presynaptic neuron.

Norepinephrine (NE) is released from noradrenergic neurons that innervate both the CNS and PNS. NE, also known as noradrenaline (NA), has an important role in controlling mood, arousal, memory, learning, and pain perception. NE is a part of the sympathetic nervous system. Dysregulation of the removal of norepinephrine by NET is associated with many neuropsychiatric diseases, discussed below. In addition, many antidepressants and recreational drugs compete for the binding of NET with NE.

Transport Mechanisms

The transport of norepinephrine back into presynaptic cell is made possible by the cotransport with Na+ and Cl−. The sequential binding of the ions results in the eventual reuptake of norepinephrine. The ion gradients of Na+ and Cl− make this reuptake energetically favorable. The gradient is generated by the Na+/K+-ATPase which transports three sodium ions out and two potassium ions into the cell. NETs have conductances similar to those of ligand-gated ion channels. The expression of NET results in a leak-channel activity.

Location in the Nervous System

NETs are restricted to noradrenergic neurons and are not present on neurons that release dopamine or epinephrine. The transporters can be found along the cell body, axons, and dendrites of the neuron. NETs are located away from the synapse, where norepinephrine is released. They are found closer to the plasma membrane of the cell. This requires norepinephrine to diffuse from the site it is released to the transporter for reuptake. Norepinephrine transporters are confined to the neurons of the sympathetic system, and those innervating the adrenal medulla, lung, and placenta.

Regulation

Regulation of NET function is complex and a focus of current research. NETs are regulated at both the cellular and molecular level post-translation. The most understood mechanisms include phosphorylation by the second messenger protein kinase C (PKC). PKC has been shown to inhibit NET function by sequestration of the transporter from the plasma membrane. The amino acid sequence of NET has shown multiple sites related to protein kinase phosphorylation. Post-translational modifications can have a wide range of effects on the function of the NET, including the rate of fusion of NET-containing vesicles with the plasma membrane, and transporter turnover.

Clinical Significance

Orthostatic Intolerance

Orthostatic intolerance (OI) is a disorder of the autonomic nervous system (a subcategory of dysautonomia) characterised by the onset of symptoms upon standing. Symptoms include fatigue, lightheadedness, headache, weakness, increased heart rate/heart palpitations, anxiety, and altered vision. Often, patients have high plasma norepinephrine (NE) concentrations (at least 600 pg/ml) in relation to sympathetic outflow upon standing, suggesting OI is a hyperadrenergic condition. The discovery of identical twin sisters who both had OI suggested a genetic basis for the disorder. A missense mutation on the NET gene (SLC6A2) was discovered in which an alanine residue was replaced with a proline residue (Ala457Pro) in a highly conserved region of the transporter. The patients’ defective NET had only 2% of the activity of the wild-type version of the gene. The genetic defect in the NET protein results in decreased NET activity that could account for abnormally high NE plasma levels in OI. However, 40 other OI patients did not have the same missense mutation, indicating other factors contributed to the phenotype in the identical twins. This discovery of the linkage with NET mutations that results in decreased norepinephrine reuptake activity and orthostatic intolerance suggests faulty NE uptake mechanisms can contribute to cardiovascular disease.

Therapeutic Uses

Inhibition of the norepinephrine transporter (NET) has potential therapeutic applications in the treatment of attention deficit hyperactivity disorder (ADHD), substance abuse, neurodegenerative disorders (e.g. Alzheimer’s disease (AD) and Parkinson’s disease (PD)) and clinical depression.

Major Depressive Disorder

Refer to Major Depressive Disorder.

Certain antidepressant medications act to raise noradrenaline, such as serotonin-norepinephrine reuptake inhibitors (SNRIs), norepinephrine-dopamine reuptake inhibitors (NDRIs), norepinephrine reuptake inhibitors (NRIs or NERIs) and the tricyclic antidepressants (TCAs). The mechanism by which these medications work is that the reuptake inhibitors prevent the reuptake of serotonin and norepinephrine by the presynaptic neuron, paralysing the normal function of the NET. At the same time, higher levels of 5-HT are maintained in the synapse increasing the concentrations of the latter neurotransmitters. Since the noradrenaline transporter is responsible for most of the dopamine clearance in the prefrontal cortex, SNRIs block reuptake of dopamine too, accumulating the dopamine in the synapse. However, DAT, the primary way dopamine is transported out of the cell, can work to decrease dopamine concentration in the synapse when the NET is blocked. For many years, the number one choice in treating mood disorders like depression was through administration of TCAs, such as desipramine (Norpramin), nortriptyline (Arentyl, Pamelor), protriptyline (Vivactil), and amoxapine (Asendin). SSRIs, which mainly regulate serotonin, subsequently replaced tricyclics as the primary treatment option for depression because of their better tolerability and lower incidence of adverse effects.

ADHD

Many drugs exist in the treatment of ADHD. Dextroamphetamine (Dexedrine, Dextrostat), Adderall, methylphenidate (Ritalin, Metadate, Concerta, Daytrana), and lisdexamfetamine (Vyvanse) block reabsorption of the catecholamines dopamine and norepinephrine through monoamine transporters (including NET), thereby increasing levels of these neurotransmitters in the brain. The strong selective norepinephrine reuptake inhibitor (NRI), atomoxetine (Strattera), has been approved by the US Food and Drug Administration (FDA) to treat ADHD in adults. The role of the NET in ADHD is similar to how it works to ease the symptoms of depression. The NET is blockaded by atomoxetine and increases NE levels in the brain. It can work to increase one’s ability to focus, decrease any impulsiveness, and lessen hyperactivity in both children and adults with ADHD.

Psychostimulants

Cocaine

Cocaine is a powerful psychostimulant and known to be one of the most widely used substances recreationally. Cocaine is a nonselective, reuptake inhibitor of the norepinephrine, serotonin, and dopamine transporters. This thwarts the absorption of these chemicals into the presynaptic terminal and allows a large concentration of dopamine, serotonin and norepinephrine to build up in the synaptic cleft. The potential for cocaine addiction is thought to be a result of its effects on dopamine transporters in the CNS, while it has been suggested that the life-threatening cardiovascular effects of cocaine may involve the inhibition of NETs at sympathetic and CNS autonomic synapses.

Amphetamines

Amphetamines have an effect on norepinephrine levels similar to that of cocaine in that they both increase NE levels in the brain. Amphetamine-like drugs are substrates for monoamine transporters, include NET, that cause a reversal in the direction of neurotransmitter transport. Amphetamines cause a large accumulation of extracellular NE. High levels of NE in the brain account for most of the profound effects of amphetamines, including alertness and anorectic, locomotor and sympathomimetic effects. However, the effects that amphetamines have on the brain are slower but last longer than the effects cocaine has on the brain. MDMA (3,4-Methylenedioxymethamphetamine or “ecstasy”) is an amphetamine with wide recreational use. A study reported that the NET inhibitor reboxetine reduced the stimulant effects of MDMA in humans, demonstrating the crucial role NET has in the cardiovascular and stimulant-like effects of MDMA.

Further Research

The role of the NET in many brain disorders underlies the importance of understanding the (dys)regulation of the transporter. A complete model of the proteins that associate with the transporter will be useful in designing drug therapies for diseases such as schizophrenia, affective disorder, and autonomic disorders. Recently discovered mechanisms of the NET, including the ability to act reversibly and as an ion channel, provide other areas of research.

Schizophrenia

Refer to Schizophrenia.

The role of NE in schizophrenia has not been fully understood, but has stimulated research into this topic. The only relationship that has been understood between researchers is that there is a positive correlation between increased NE levels in the brain and spinal fluid (CSF) and activity of schizophrenia. In one study, clonidine, a drug used to treat medical conditions such as ADHD and high blood pressure, was shown to produce a significant decrease in plasma level MHPG (3-methoxy-4-hydroxyphenylglycol), a metabolite of NE, in the normal control group, but not in the group of schizophrenic patients. This suggests that in schizophrenia, the alpha-2 adrenergic receptor, a presynaptic inhibitory receptor, may be less sensitive compared to normally functioning alpha-2 receptors and thus relate to elevated NE levels in the disorder. In addition to increased NE levels in the brain and CSF, increased levels of MHPG has also been associated with a diagnosis of schizophrenia. Impaired NE regulation in schizophrenia has been an area of interest for researchers and research on this topic is still ongoing.

Imaging

Via positron emission tomography imaging technique, NET has been selectively investigated. 11C ME@HAPTHI and 18F-MeNER are two NET selective radio tracers for PET imaging. Fluorescent substrates for the transporter can also be used to monitor the transporter rate in isolated organs or tissues, although these are not suitable for clinical imaging.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Norepinephrine_transporter >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is a Serotonin Transporter?

Published on by Andrew Marshall9 Comments

Introduction

The serotonin transporter (SERT or 5-HTT) also known as the sodium-dependent serotonin transporter and solute carrier family 6 menmber 4 is a protein that in humans is encoded by the SLC6A4 gene. SERT is a type of monoamine transporter protein that transports the neurotransmitter serotonin from the synaptic cleft back to the presynaptic neuron, in a process known as serotonin reuptake.

This transport of serotonin by the SERT protein terminates the action of serotonin and recycles it in a sodium-dependent manner. Many antidepressant medications of the SSRI and tricyclic antidepressant classes work by binding to SERT and thus reducing serotonin reuptake. It is a member of the sodium:neurotransmitter symporter family. A repeat length polymorphism in the promoter of this gene has been shown to affect the rate of serotonin uptake and may play a role in sudden infant death syndrome, aggressive behaviour in Alzheimer disease patients, post-traumatic stress disorder and depression-susceptibility in people experiencing emotional trauma.

Mechanism of Action

Serotonin-reuptake transporters are dependent on both the concentration of potassium ion in the cytoplasm and the concentrations of sodium and chloride ions in the extracellular fluid. In order to function properly the serotonin transporter requires the membrane potential created by the sodium-potassium adenosine triphosphatase.

The serotonin transporter first binds a sodium ion, followed by the serotonin, and then a chloride ion; it is then allowed, thanks to the membrane potential, to flip inside the cell freeing all the elements previously bound. Right after the release of the serotonin in the cytoplasm a potassium ion binds to the transporter which is now able to flip back out returning to its active state.

Function

The serotonin transporter removes serotonin from the synaptic cleft back into the synaptic boutons. Thus, it terminates the effects of serotonin and simultaneously enables its reuse by the presynaptic neuron.

Neurons communicate by using chemical messengers like serotonin between cells. The transporter protein, by recycling serotonin, regulates its concentration in a gap, or synapse, and thus its effects on a receiving neuron’s receptors.

Medical studies have shown that changes in serotonin transporter metabolism appear to be associated with many different phenomena, including alcoholism, clinical depression, obsessive–compulsive disorder (OCD), romantic love, hypertension and generalized social phobia.

The serotonin transporter is also present in platelets; there, serotonin functions as a vasoconstrictive substance. It also serves as a signalling molecule to induce platelet aggregation.

Pharmacology

In 1995 and 1996, scientists in Europe had identified the polymorphism 5-HTTLPR, a serotonin-transporter in the gene SLC6A4. In December 1996, a group of researchers led by D.A. Collier of the Institute of Psychiatry, Psychology and Neuroscience, published their findings in Molecular Psychiatry, that, “5-HTTLPR-dependent variation in functional 5-HTT expression is a potential genetic susceptibility factor for affective disorders.”

SERT spans the plasma membrane 12 times. It belongs to the NE, DA, SERT monoamine transporter family. Transporters are important sites for agents that treat psychiatric disorders. Drugs that reduce the binding of serotonin to transporters (serotonin reuptake inhibitors, or SRIs) are used to treat mental disorders. The selective serotonin reuptake inhibitor (SSRI) fluoxetine and the tricyclic antidepressant (TCA) clomipramine are examples of serotonin reuptake inhibitors.

Following the elucidation of structures of the homologous bacterial transporter, LeuT, co-crystallised with tricyclic antidepressants in the vestibule leading from the extracellular space to the central substrate site it was inferred that this binding site did also represent the binding site relevant for antidepressant binding in SERT. However, studies on SERT showed that tricyclic antidepressants and selective serotonin reuptake inhibitors bind to the central binding site overlapping the substrate binding site. The Drosophila dopamine transporter, which displays a pharmacology similar to SERT, was crystallised with tricyclic antidepressants and confirmed the earlier finding that the substrate binding site is also the antidepressant binding site.

Ligands

  • DASB, also known as 3-amino-4-(2-dimethylaminomethylphenylsulfanyl)-benzonitrile, is a compound that binds to the serotonin transporter.
  • compound 4b: Ki = 17 pM; 710-fold and 11,100-fold selective over DAT and NET
  • compound (+)-12a: Ki = 180 pM at hSERT; >1000-fold selective over hDAT, hNET, 5-HT1A, and 5-HT6. Isosteres
  • 3-cis-(3-Aminocyclopentyl)indole 8a: Ki = 220 pM
  • allosteric modulator: 3′-Methoxy-8-methyl-spiro{8-azabicyclo[3.2.1]octane-3,5′(4′H)-isoxazole} (compound 7a)
  • allosteric modulator: p-Trifluoromethyl-methcathinone

Genetics

The gene that encodes the serotonin transporter is called solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 (SLC6A4, refer to Solute carrier family). In humans the gene is found on chromosome 17 on location 17q11.1–q12.

Mutations associated with the gene may result in changes in serotonin transporter function, and experiments with mice have identified more than 50 different phenotypic changes as a result of genetic variation. These phenotypic changes may, e.g., be increased anxiety and gut dysfunction. Some of the human genetic variations associated with the gene are:

  • Length variation in the serotonin-transporter-gene-linked polymorphic region (5-HTTLPR)
  • rs25531 — a single nucleotide polymorphism (SNP) in the 5-HTTLPR
  • rs25532 — another SNP in the 5-HTTLPR
  • STin2 — a variable number of tandem repeats (VNTR) in the functional intron 2
  • G56A on the second exon
  • I425V on the ninth exon

Length Variation in 5-HTTLPR

Refer to 5-HTTLPR.

According to a 1996 article in The Journal of Neurochemistry, the promoter region of the SLC6A4 gene contains a polymorphism with “short” and “long” repeats in a region: 5-HTT-linked polymorphic region (5-HTTLPR or SERTPR). The short variation has 14 repeats of a sequence while the long variation has 16 repeats. A second 1996 article stated that the short variation leads to less transcription for SLC6A4, and it has been found that it can partly account for anxiety-related personality traits. This polymorphism has been extensively investigated in over 300 scientific studies (as of 2006). The 5-HTTLPR polymorphism may be subdivided further: One study published in 2000 found 14 allelic variants (14-A, 14-B, 14-C, 14-D, 15, 16-A, 16-B, 16-C, 16-D, 16-E, 16-F, 19, 20 and 22) in a group of around 200 Japanese and Caucasian people.

In addition to altering the expression of SERT protein and concentrations of extracellular serotonin in the brain, the 5-HTTLPR variation is associated with changes in brain structure. One 2005 study found less grey matter in perigenual anterior cingulate cortex and amygdala for short allele carriers of the 5-HTTLPR polymorphism compared to subjects with the long/long genotype.

In contrast, a 2008 meta-analysis found no significant overall association between the 5-HTTLPR polymorphism and autism. A hypothesized gene–environment interaction between the short/short allele of the 5-HTTLPR and life stress as predictor for major depression has suffered a similar fate: after an influential initial report in 2003 there were mixed results in replication in 2008, and a 2009 meta-analysis was negative.

rs25532

rs25532 is a SNP (C>T) close to the site of 5-HTTLPR. It has been examined in connection with obsessive compulsive disorder (OCD).

I425V

I425V is a rare mutation on the ninth exon. In 2003, researchers from Japan and the US reported that they had found this genetic variation in unrelated families with OCD, and have found that it leads to faulty transporter function and regulation. A second variant in the same gene of some patients with this mutation suggests a genetic “double hit”, resulting in greater biochemical effects and more severe symptoms.

VNTR in STin2

Another noncoding polymorphism is a VNTR in the second intron (STin2). In a 2005 study, it was found with three alleles: 9, 10 and 12 repeats. A meta-analysis has found that the 12 repeat allele of the STin2 VNTR polymorphism had some minor (with odds ratio 1.24), but statistically significant, association with schizophrenia. A 2008 meta-analysis found no significant overall association between the STin2 VNTR polymorphism and autism. Furthermore, a 2003 meta-analysis of affective disorders, major depressive disorder and bipolar disorder, found a minor association to the intron 2 VNTR polymorphism, but the results of the meta-analysis were dependent upon a large effect from one individual study.

The polymorphism has also been related to personality traits with a 2008 Russian study finding individuals with the STin2.10 allele having lower neuroticism scores as measured with the Eysenck Personality Inventory.

Neuroimaging

The distribution of the serotonin transporter in the brain may be imaged with positron emission tomography using radioligands called DASB and DAPP; the first such studies on the human brain were reported in 2000. DASB and DAPP are not the only radioligands for the serotonin transporter. There are numerous others, with the most popular probably being the β-CIT radioligand with an iodine-123 isotope that is used for brain scanning with single-photon emission computed tomography (SPECT) according to a 1993 article in the Journal of Neural Transmission. The radioligands were used in 2006 to examine whether variables such as age, gender or genotype are associated with differential serotonin transporter binding. Healthy subjects that have a high score of neuroticism—a personality trait in the Revised NEO Personality Inventory—were found to have more serotonin transporter binding in the thalamus in 2007.

Neuroimaging and Genetics

Studies on the serotonin transporter have combined neuroimaging and genetics methods, e.g., a voxel-based morphometry study found less grey matter in perigenual anterior cingulate cortex and amygdala for short allele carriers of the 5-HTTLPR polymorphism compared to subjects with the long/long genotype.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Serotonin_transporter >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is a Reuptake Inhibitor?

Published on by Andrew Marshall4 Comments

Introduction

A reuptake inhibitor (RI) is a type of drug known as a reuptake modulator that inhibits the plasmalemmal transporter-mediated reuptake of a neurotransmitter from the synapse into the pre-synaptic neuron. This leads to an increase in extracellular concentrations of the neurotransmitter and an increase in neurotransmission. Various drugs exert their psychological and physiological effects through reuptake inhibition, including many antidepressants and psychostimulants.

Most known reuptake inhibitors affect the monoamine neurotransmitters serotonin, norepinephrine (and epinephrine), and dopamine. However, there are also a number of pharmaceuticals and research chemicals that act as reuptake inhibitors for other neurotransmitters such as glutamate, γ-aminobutyric acid (GABA), glycine, adenosine, choline (the precursor of acetylcholine), and the endocannabinoids, among others.

Mechanism of Action

Active Site Transporter Substrates

Standard reuptake inhibitors are believed to act simply as competitive substrates that work by binding directly to the plasmalemma transporter of the neurotransmitter in question. They occupy the transporter in place of the respective neurotransmitter and competitively block it from being transported from the nerve terminal or synapse into the pre-synaptic neuron. With high enough doses, occupation becomes as much as 80–90%. At this level of inhibition, the transporter will be considerably less efficient at removing excess neurotransmitter from the synapse and this causes a substantial increase in the extracellular concentrations of the neurotransmitter and therefore an increase in overall neurotransmission.

Allosteric Site Transporter Substrates

Alternatively, some reuptake inhibitors bind to allosteric sites and inhibit reuptake indirectly and noncompetitively.

Phencyclidine and related drugs such as benocyclidine, tenocyclidine, ketamine, and dizocilpine (MK-801), have been shown to inhibit the reuptake of the monoamine neurotransmitters. They appear to exert their reuptake inhibition by binding to vaguely characterised allosteric sites on each of the respective monoamine transporters. Benztropine, mazindol, and vanoxerine also bind to these sites and have similar properties. In addition to their high affinity for the main site of the monoamine transporters, several competitive transporter substrates such as cocaine and indatraline have lower affinity for these allosteric sites as well.

A few of the selective serotonin reuptake inhibitors (SSRIs) such as the dextro-enantiomer of citalopram appear to be allosteric reuptake inhibitors of serotonin. Instead of binding to the active site on the serotonin transporter, they bind to an allosteric site, which exerts its effects by causing conformational changes in the transporter protein and thereby modulating the affinity of substrates for the active site. As a result, escitalopram has been marketed as an allosteric serotonin reuptake inhibitor. Notably, this allosteric site may be directly related to the above-mentioned PCP binding sites.

Vesicular Transporter Substrates

A second type of reuptake inhibition affects vesicular transport, and blocks the intracellular repackaging of neurotransmitters into cytoplasmic vesicles. In contrast to plasmalemmal reuptake inhibitors, vesicular reuptake inhibitors do not increase the synaptic concentrations of a neurotransmitter, only the cytoplasmic concentrations; unless, that is, they also act as plasmalemmal transporter reversers via phosphorylation of the transporter protein, also known as a releasing agent. Pure vesicular reuptake inhibitors tend to actually lower synaptic neurotransmitter concentrations, as blocking the repackaging of, and storage of the neurotransmitter in question leaves them vulnerable to degradation via enzymes such as monoamine oxidase (MAO) that exist in the cytoplasm. With vesicular transport blocked, neurotransmitter stores quickly become depleted.

Reserpine (Serpasil) is an irreversible inhibitor of the vesicular monoamine transporter 2 (VMAT2), and is a prototypical example of a vesicular reuptake inhibitor.

Indirect Unknown Mechanism

Two of the primary active constituents of the medicinal herb Hypericum perforatum (St. John’s Wort) are hyperforin and adhyperforin. Hyperforin and adhyperforin are wide-spectrum inhibitors of the reuptake of serotonin, norepinephrine, dopamine, glutamate, GABA, glycine, and choline, and they exert these effects by binding to and activating the transient receptor potential cation channel TRPC6. Activation of TRPC6 induces the entry of calcium (Ca2+) and sodium (Na+) into the cell, which causes the effect through unknown mechanism.

Types

Typical

  • Amino acid reuptake inhibitor:
    • Excitatory amino acid reuptake inhibitor (or glutamate-aspartate reuptake inhibitor)
    • GABA reuptake inhibitor
    • Glycine reuptake inhibitor
  • Monoamine reuptake inhibitor:
    • Dopamine reuptake inhibitor
    • Norepinephrine reuptake inhibitor
    • Serotonin reuptake inhibitor
    • Serotonin-norepinephrine reuptake inhibitor
    • Norepinephrine-dopamine reuptake inhibitor
    • Serotonin-dopamine reuptake inhibitor
    • Serotonin-norepinephrine-dopamine reuptake inhibitor
  • Miscellaneous:
    • Adenosine reuptake inhibitor
    • Endocannabinoid reuptake inhibitor

Atypical

  • TRPC6 activators (wide-spectrum reuptake inhibitors) – hyperforin, adhyperforin

Plasmalemmal

  • Choline reuptake inhibitor – hemicholinium-3, triethylcholine

Vesicular

  • Vesicular acetylcholine transporter (VAChT) inhibitor – vesamicol
  • Vesicular monoamine transporter (VMAT) inhibitor – reserpine, tetrabenazine

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Reuptake_inhibitor >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is Trazodone?

Published on by Andrew Marshall4 Comments

Introduction

Trazodone, sold under many brand names, is an antidepressant medication. It is used to treat major depressive disorder, anxiety disorders, and difficulties with sleep. The medication is taken orally.

Common side-effects include dry mouth, feeling faint, vomiting, and headache. More serious side effects may include suicide, mania, irregular heart rate, and pathologically prolonged erections. It is unclear if use during pregnancy or breastfeeding is safe. It is a phenylpiperazine compound of the serotonin antagonist and reuptake inhibitor (SARI) class. Trazodone also has sedating effects.

Trazodone was approved for medical use in the United States in 1981. It is available as a generic medication. In 2020, it was the 21st most commonly prescribed medication in the United States, with more than 26 million prescriptions.

Brief History

Trazodone was developed in Italy, in the 1960s, by Angelini Research Laboratories as a second-generation antidepressant. It was developed according to the mental pain hypothesis, which was postulated from studying patients and which proposes that major depression is associated with a decreased pain threshold. In sharp contrast to most other antidepressants available at the time of its development, trazodone showed minimal effects on muscarinic cholinergic receptors. Trazodone was patented and marketed in many countries all over the world. It was approved by the Food and Drug Administration (FDA) in 1981 and was the first non-tricyclic or MAOI antidepressant approved in the US.

Medical Uses

Depression

The primary use of trazodone is the treatment of unipolar major depression with or without anxiety. Data from open and double-blind trials suggest the antidepressant efficacy of trazodone is comparable to that of amitriptyline, doxepin, and mianserin. Also, trazodone showed anxiolytic properties, low cardiotoxicity, and relatively mild side effects.

Because trazodone has minimal anticholinergic activity, it was especially welcomed as a treatment for geriatric patients with depression when it first became available. Three double-blind studies reported trazodone has antidepressant efficacy similar to that of other antidepressants in geriatric patients. However, a side effect of trazodone, orthostatic hypotension, which may cause dizziness and increase the risk of falling, can have devastating consequences for elderly patients; thus, this side effect, along with sedation, often makes trazodone less acceptable for this population, compared with newer compounds that share its lack of anticholinergic activity but not the rest of its side-effect profile. Still, trazodone is often helpful for geriatric patients with depression who have severe agitation and insomnia.

Trazodone is usually used at a dosage of 150 to 300 mg/day for the treatment of depression. Lower doses have also been used to augment other antidepressants, or when initiating therapy. Higher doses up to 600 mg/day have been used in more severe cases of depression, for instance in hospitalised patients. Trazodone is usually administered multiple times per day, but once-daily administration may be similarly effective.

Insomnia

Low-dose trazodone is used off-label in the treatment of insomnia and is considered to be effective and safe for this indication. It may also be used to treat antidepressant-related insomnia. Trazodone was the second-most prescribed agent for insomnia in the early 2000s, though most studies of trazodone for treatment of sleep disturbances have been in depressed individuals.

Systematic reviews and meta-analyses published in the late 2010s, including a Cochrane review, found low-dose trazodone to be an effective medication for short-term treatment of insomnia both in depressed and non-depressed people. Trazodone slightly improves subjective sleep quality (SMD = –0.34 to –0.41) and reduces number of nighttime awakenings (MD = –0.31, SMD = –0.51). Conversely, it does not appear to affect sleep onset, total sleep time, time awake after sleep onset, or sleep efficiency. It appears to increase deep sleep, in contrast to certain other hypnotics. The quality of evidence of trazodone for short-term treatment of insomnia was rated as low to moderate. There is no evidence available at present to inform long-term use of trazodone in the treatment of insomnia.

The benefits of trazodone for insomnia must be weighed against potential adverse effects such as morning grogginess, daytime sleepiness, cognitive and motor impairment, and postural hypotension, among others. Quality safety data on use of trazodone as a sleep aid are currently lacking.

Trazodone is used at low doses in the range of 25 to 150 mg/day for insomnia. Higher doses of 200 to 600 mg/day have also been studied.

The American Academy of Sleep Medicine’s 2017 clinical practice guidelines recommended against the use of trazodone in the treatment of insomnia due to inadequate evidence and due to harms potentially outweighing benefits.

Other Disorders

Trazodone is often used in the treatment of anxiety disorders such as generalised anxiety disorder, panic disorder, post-traumatic stress disorder (PTSD), and obsessive–compulsive disorder (OCD). However, use of trazodone in anxiety disorders is off-label and evidence of its effectiveness for these indications is variable and limited. Benefits for OCD appear to be mild. Besides anxiety, trazodone has been used to treat sleep disturbances and nightmares in PTSD. Trazodone is often used as an alternative to benzodiazepines in the treatment of anxiety disorders.

Combination with Other Antidepressants

Trazodone is often used in combination with other antidepressants such as selective serotonin reuptake inhibitors (SSRI) in order to augment their antidepressant and anxiolytic effects and to reduce side effects such as sexual dysfunction, anxiety, and insomnia.

Available Forms

Trazodone is provided as the hydrochloride salt and is available in the form of 50 mg, 100 mg, 150 mg, and 300 mg oral tablets.

An extended-release oral tablet formulation at doses of 150 mg and 300 mg is also available.

Side Effects

Because of its lack of anticholinergic side effects, trazodone is especially useful in situations in which antimuscarinic effects are particularly problematic (e.g. in patients with benign prostatic hyperplasia, closed-angle glaucoma, or severe constipation). Trazodone’s propensity to cause sedation is a dual-edged sword. For many patients, the relief from agitation, anxiety, and insomnia can be rapid; for other patients, including those individuals with considerable psychomotor retardation and feelings of low energy, therapeutic doses of trazodone may not be tolerable because of sedation. Trazodone elicits orthostatic hypotension in some people, probably as a consequence of α1-adrenergic receptor blockade. The unmasking of bipolar disorder may occur with trazodone and other antidepressants.

Precautions for trazodone include known hypersensitivity to trazodone and under 18 years and combined with other antidepressant medications, it may increase the possibility of suicidal thoughts or actions.

While trazodone is not a true member of the SSRI class of antidepressants, it does still share many properties of SSRIs, especially the possibility of discontinuation syndrome if the medication is stopped too quickly. Care must, therefore, be taken when coming off the medication, usually by a gradual process of tapering down the dose over a period of time.

Suicide

Antidepressants may increase the risk of suicidal thoughts and behaviours in children and young adults. Close monitoring for emergence of suicidal thoughts and behaviours is thus recommended.

Sedation

Since trazodone may impair the mental and/or physical abilities required for performance of potentially hazardous tasks, such as operating an automobile or machinery, the patient should be cautioned not to engage in such activities while impaired. Compared to the reversible MAOI antidepressant drug moclobemide, more impairment of vigilance occurs with trazodone. Trazodone has been found to impair driving ability.

Cardiac

Case reports have noted cardiac arrhythmias emerging in relation to trazodone treatment, both in patients with pre-existing mitral valve prolapse and in patients with negative personal and family histories of cardiac disease.

QT prolongation has been reported with trazodone therapy. Arrhythmia identified include isolated PVCs, ventricular couplets, and in two patients short episodes (three to four beats) of ventricular tachycardia. Several post-marketing reports have been made of arrhythmia in trazodone-treated patients who have pre-existing cardiac disease and in some patients who did not have pre-existing cardiac disease. Until the results of prospective studies are available, patients with pre-existing cardiac disease should be closely monitored, particularly for cardiac arrhythmias. Trazodone is not recommended for use during the initial recovery phase of myocardial infarction. Concomitant administration of drugs that prolong the QT interval or that are inhibitors of CYP3A4 may increase the risk of cardiac arrhythmia.

Priapism

A relatively rare side effect associated with trazodone is priapism, likely due to its antagonism at α-adrenergic receptors. More than 200 cases have been reported, and the manufacturer estimated that the incidence of any abnormal erectile function is about one in 6,000 male patients treated with trazodone. The risk for this side effect appears to be greatest during the first month of treatment at low dosages (i.e. <150 mg/day). Early recognition of any abnormal erectile function is important, including prolonged or inappropriate erections, and should prompt discontinuation of trazodone treatment. Spontaneous orgasms have also been reported with trazodone in men.

Clinical reports have described trazodone-associated psychosexual side effects in women as well, including increased libido, priapism of the clitoris, and spontaneous orgasms.

Others

Rare cases of liver toxicity have been observed, possibly due to the formation of reactive metabolites.

Elevated prolactin concentrations have been observed in people taking trazodone. They appear to be increased by around 1.5- to 2-fold.

Studies on trazodone and cognitive function are mixed, with some finding improvement, others finding no change, and some finding impairment.

Trazodone does not seem to worsen periodic limb movements during sleep.

Trazodone is associated with increased risk of falls in older adults. It has also been associated with increased risk of hip fractures in older adults.

Pregnancy and Lactation

Sufficient data in humans are lacking. Use should be justified by the severity of the condition to be treated.

Overdose

There are reported cases of high doses of trazodone precipitating serotonin syndrome. There are also reports of patients taking multiple SSRIs with trazodone and precipitating serotonin syndrome.

Trazodone appears to be relatively safer than TCAs, MAOIs, and a few of the other second-generation antidepressants in overdose situations, especially when it is the only agent taken. Fatalities are rare, and uneventful recoveries have been reported after ingestion of doses as high as 6,000–9,200 mg. In one report, 9 of 294 cases of overdose were fatal, and all nine patients had also taken other central nervous system (CNS) depressants. When trazodone overdoses occur, clinicians should carefully monitor for low blood pressure, a potentially serious toxic effect. In a report of a fatal trazodone overdose, torsades de pointes and complete atrioventricular block developed, along with subsequent multiple organ failure, with a trazodone plasma concentration of 25.4 mg/L on admission.

Interactions

Trazodone is metabolised by several liver enzymes, including CYP3A4, CYP2D6, and CYP1A2. Its active metabolite meta-chlorophenylpiperazine (mCPP) is known to be formed by CYP3A4 and metabolized by CYP2D6. Inhibition or induction of the aforementioned enzymes by various other substances may alter the metabolism of trazodone and/or mCPP, leading to increased and/or decreased blood concentrations. The enzymes in question are known to be inhibited and induced by many medications, herbs, and foods, and as such, trazodone may interact with these substances. Potent CYP3A4 inhibitors such as clarithromycin, erythromycin, fluvoxamine, grapefruit juice, ketoconazole, and ritonavir may lead to increased concentrations of trazodone and decreased concentrations of mCPP, while CYP3A4 inducers like carbamazepine, enzalutamide, phenytoin, phenobarbital, and St. John’s wort may result in decreased trazodone concentrations and increased mCPP concentrations. CYP2D6 inhibitors may result in increased concentrations of both trazodone and mCPP while CYP2D6 inducers may decrease their concentrations. Examples of potent CYP2D6 inhibitors include bupropion, cannabidiol, duloxetine, fluoxetine, paroxetine, quinidine, and ritonavir, while CYP2D6 inducers include dexamethasone, glutethimide, and haloperidol. CYP1A2 inhibitors may increase trazodone concentrations while CYP1A2 inducers may decrease trazodone concentrations. Examples of potent CYP1A2 inhibitors include ethinylestradiol (found in hormonal birth control), fluoroquinolones (e.g. ciprofloxacin), fluvoxamine, and St. John’s wort, while potent CYP1A2 inducers include phenytoin, rifampin, ritonavir, and tobacco.

A study found that ritonavir, a strong CYP3A4 and CYP2D6 inhibitor and moderate CYP1A2 inducer, increased trazodone peak levels by 1.34-fold, increased area-under-the-curve levels by 2.4-fold, and decreased the clearance of trazodone by 50%. This was associated with adverse effects such as nausea, hypotension, and syncope. Another study found that the strong CYP3A4 inducer carbamazepine reduced concentrations of trazodone by 60 to 74%. The strong CYP2D6 inhibitor thioridazine has been reported to increase concentrations of trazodone by 1.36-fold and concentrations of mCPP by 1.54-fold. On the other hand, CYP2D6 genotype has not been found to predict trazodone or mCPP concentrations with trazodone therapy, although it did correlate with side effects like dizziness and prolonged corrected QT interval.

Combination of trazodone with SSRIs, tricyclic antidepressants (TCAs), or monoamine oxidase inhibitors has a theoretical risk of serotonin syndrome. However, trazodone has been studied in combination with SSRIs and seemed to be safe in this context. On the other hand, cases of excessive sedation and serotonin syndrome have been reported with the combinations of trazodone and fluoxetine or paroxetine. This may be due to combined potentiation of the serotonin system. However, it may also be related to the fact that fluoxetine and paroxetine are strong inhibitors of CYP2D6 and fluoxetine is additionally a weak or moderate inhibitor of CYP3A4. Accordingly, fluoxetine has been reported to result in increased levels of trazodone and mCPP by 1.31- to 1.65-fold and by 2.97- to 3.39-fold, respectively.

Smokers have lower levels of trazodone and higher ratios of mCPP to trazodone. Trazodone levels were 30% lower in smokers and mCPP to trazodone ratio was 1.29-fold higher in smokers, whereas mCPP concentrations were not different between smokers and non-smokers. Smoking is known to induce CYP1A2, and this may be involved in these findings.

Pharmacology

Pharmacodynamics

Trazodone is a mixed agonist and antagonist of various serotonin receptors, antagonist of adrenergic receptors, weak histamine H1 receptor antagonist, and weak serotonin reuptake inhibitor. More specifically, it is an antagonist of 5-HT2A and 5-HT2B receptors, a partial agonist of the 5-HT1A receptor, and an antagonist of the α1- and α2-adrenergic receptors.It is also a ligand of the 5-HT2C receptor with lower affinity than for the 5-HT2A receptor. However, it is unknown whether trazodone acts as a full agonist, partial agonist, or antagonist of the 5-HT2C receptor. Trazodone is a 5-HT1A receptor partial agonist similarly to buspirone and tandospirone but with comparatively greater intrinsic activity. A range of weak affinities (Ki) have been reported for trazodone at the human histamine H1 receptor, including 220 nM, 350 nM, 500 nM, and 1,100 nM.

Trazodone has a minor active metabolite known as meta-chlorophenylpiperazine (mCPP), and this metabolite may contribute to some degree to the pharmacological properties of trazodone. In contrast to trazodone, mCPP is an agonist of various serotonin receptors. It has relatively low affinity for α1-adrenergic receptors unlike trazodone, but does high affinity for α2-adrenergic receptors and weak affinity for the H1 receptor. In addition to direct interactions with serotonin receptors, mCPP is a serotonin releasing agent similarly to agents like fenfluramine and MDMA. In contrast to these serotonin releasing agents however, mCPP does not appear to cause long-term serotonin depletion (a property thought to be related to serotonergic neurotoxicity).

Trazodone’s 5-HT2A receptor antagonism and weak serotonin reuptake inhibition form the basis of its common label as an antidepressant of the serotonin antagonist and reuptake inhibitor (SARI) type.

Target Occupancy Studies

Studies have estimated occupancy of target sites by trazodone based on trazodone concentrations in blood and brain and on the affinities of trazodone for the human targets in question. Roughly half of brain 5-HT2A receptors are blocked by 1 mg of trazodone and essentially all 5-HT2A receptors are saturated at 10 mg of trazodone, but the clinically effective hypnotic doses of trazodone are in the 25–100 mg range. The occupancy of the serotonin transporter (SERT) by trazodone is estimated to be 86% at 100 mg/day and 90% at 150 mg/day. Trazodone may almost completely occupy the 5-HT2A and 5-HT2C receptors at doses of 100 to 150 mg/day. Significant occupancy of a number of other sites may also occur. However, another study estimated much lower occupancy of the SERT and 5-HT2A receptors by trazodone.

Correspondence to Clinical Effects

Trazodone may act predominantly as a 5-HT2A receptor antagonist to mediate its therapeutic benefits against anxiety and depression. Its inhibitory effects on serotonin reuptake and 5-HT2C receptors are comparatively weak. In relation to these properties, trazodone does not have similar properties to SSRIs and is not particularly associated with increased appetite and weight gain – unlike other 5-HT2C antagonists like mirtazapine. Moderate 5-HT1A partial agonism may contribute to trazodone’s antidepressant and anxiolytic actions to some extent as well.

The combined actions of 5-HT2A and 5HT2C receptor antagonism with serotonin reuptake inhibition only occur at moderate to high doses of trazodone. Doses of trazodone lower than those effective for antidepressant action are frequently used for the effective treatment of insomnia. Low doses exploit trazodone’s potent actions as a 5-HT2A receptor antagonist, and its properties as an antagonist of H1 and α1-adrenergic receptors, but do not adequately exploit its SERT or 5-HT2C inhibition properties, which are weaker. Since insomnia is one of the most frequent residual symptoms of depression after treatment with an SSRI, a hypnotic is often necessary for patients with a major depressive episode. Not only can a hypnotic potentially relieve the insomnia itself, but treating insomnia in patients with major depression may also increase remission rates due to improvement of other symptoms such as loss of energy and depressed mood. Thus, the ability of low doses of trazodone to improve sleep in depressed patients may be an important mechanism whereby trazodone can augment the efficacy of other antidepressants.

Trazodone’s potent α1-adrenergic blockade may cause some side effects like orthostatic hypotension and sedation. Conversely, along with 5-HT2A and H1 receptor antagonism, it may contribute to its efficacy as a hypnotic. Trazodone lacks any affinity for the muscarinic acetylcholine receptors, so does not produce anticholinergic side effects.

mCPP, a non-selective serotonin receptor modulator and serotonin releasing agent, is an active metabolite of trazodone and has been suggested to possibly play a role in its therapeutic benefits. However, research has not supported this hypothesis and mCPP might actually antagonise the efficacy of trazodone as well as produce additional side effects.

Pharmacokinetics

Absorption

Trazodone is well-absorbed after oral administration. Its bioavailability is 65 to 80%. Peak blood levels of trazodone occur 1 to 2 hours after ingestion and peak levels of the metabolite mCPP occur after 2 to 4 hours. Absorption is somewhat delayed and enhanced by food.

Distribution

Trazodone is not sequestered into any tissue. The medication is 89 to 95% protein-bound. The volume of distribution of trazodone is 0.8 to 1.5 L/kg. Trazodone is highly lipophilic.

Metabolism

The metabolic pathways involved in the metabolism are not well-characterized. In any case, the cytochrome P450 enzymes CYP3A4, CYP2D6, and CYP1A2 may all be involved to varying extents. Trazodone is known to be extensively metabolized by the liver via hydroxylation, N-oxidation, and N-dealkylation. Several metabolites of trazodone have been identified, including a dihydrodiol metabolite (via hydroxylation), a metabolite hydroxylated at the para position of the meta-chlorophenyl ring (via CYP2D6), oxotriazolepyridinepropionic acid (TPA) and mCPP (both via N-dealkylation of the piperazinyl nitrogen mediated by CYP3A4), and a metabolite formed by N-oxidation of the piperazinyl nitrogen. CYP1A2, CYP2D6, and CYP3A4 genotypes all do not seem to predict concentrations of trazodone or mCPP. In any case, there are large interindividual variations in the metabolism of trazodone. In addition, poor metabolisers of dextromethorphan, a CYP2D6 substrate, eliminate mCPP more slowly and have higher concentrations of mCPP than do extensive metabolizers.

mCPP is formed from trazodone by CYP3A4 and is metabolised via hydroxylation by CYP2D6 (to a para-hydroxylated metabolite). It may contribute to the pharmacological actions of trazodone. mCPP levels are only 10% of those of trazodone during therapy with trazodone, but is nonetheless present at concentrations known to produce psychic and physical effects in humans when mCPP has been administered alone. In any case, the actions of trazodone, such as its serotonin antagonism, might partially overwhelm those of mCPP. As a consequence of the production of mCPP as a metabolite, patients administered trazodone may test positive on EMIT II urine tests for the presence of MDMA (“ecstasy”).

Elimination

The elimination of trazodone is biphasic: the first phase’s half-life (distribution) is 3 to 6 hours, and the following phase’s half-life (elimination) is 4.1 to 14.6 hours. The elimination half-life of extended-release trazodone is 9.1 to 13.2 hours. The elimination half-life of mCPP is 2.6 to 16.0 hours and is longer than that of trazodone. Metabolites are conjugated to gluconic acid or glutathione and around 70 to 75% of 14C-labelled trazodone was found to be excreted in the urine within 72 hours. The remaining drug and its metabolites are excreted in the faeces via biliary elimination. Less than 1% of the drug is excreted in its unchanged form. After an oral dose of trazodone, it was found to be excreted 20% in the urine as TPA and conjugates, 9% as the dihydrodiol metabolite, and less than 1% as unconjugated mCPP. mCPP is glucuronidated and sulfated similarly to other trazodone metabolites.

Chemistry

Trazodone is a triazolopyridine derivative and a phenylpiperazine that is structurally related to nefazodone and etoperidone, each of which are derivatives of it. Flibanserin is an analogue of trazodone.

Society and Culture

Generic Names

Trazodone is the generic name of the drug and its INN, BAN, and DCF, while trazodone hydrochloride is its USAN, USP, BANM, and JAN.

Brand Names

Trazodone has been marketed under a large number of brand names throughout the world. Major brand names include Desyrel (worldwide), Donaren (Brazil), Molipaxin (Ireland, United Kingdom), Oleptro (United States), Trazorel (Canada), and Trittico (worldwide).

Research

Trazodone may be effective in the treatment of sexual dysfunction, for instance female sexual dysfunction and erectile dysfunction. A 2003 systematic review and meta-analysis found some indication that trazodone may be useful in the treatment of erectile dysfunction. Besides trazodone alone, a combination of trazodone and bupropion (developmental code names and tentative brand names S1P-104, S1P-205, Lorexys, and Orexa) is under development for the treatment of erectile dysfunction and female sexual dysfunction. As of September 2021, it is in phase 2 clinical trials for these indications. It has been in this stage of clinical development since at least February 2015.

Trazodone may be useful in the treatment of certain symptoms like sleep disturbances in alcohol withdrawal and recovery. However, reviews have recommended against use of trazodone for alcohol withdrawal due to inadequate evidence. Very limited evidence suggests that trazodone might be useful in the treatment of certain symptoms in cocaine use disorder. Trazodone has been reported to be effective in the treatment of sleep apnoea. Cochrane reviews found that trazodone was not effective in the treatment of agitation in dementia. Another Cochrane review found that trazodone might be useful in the treatment of sleep disturbances in dementia. Further systematic reviews have found that trazodone may be effective for behavioural and psychological symptoms in dementias such as frontotemporal dementia and Alzheimer’s disease.

Trazodone has been studied as an adjunctive therapy in the treatment of schizophrenia. It has been reported to decrease negative symptoms without worsening positive symptoms although improvement in negative symptoms was modest. Trazodone has also been reported to be effective in treating antipsychotic-related extrapyramidal symptoms such as akathisia. Trazodone has been studied and reported to be effective in the treatment of bulimia, but there is limited evidence to support this use. It might be useful in the treatment of night eating disorder as well. Trazodone might be effective in the treatment of adjustment disorder. It may also be effective in the treatment of bruxism in children and adolescents.

Trazodone may be useful in the treatment of certain chronic pain disorders. There is limited but conflicting evidence to support the use of trazodone in the treatment of headaches and migraines in children. Trazodone may be useful in the treatment of fibromyalgia as well as diabetic neuropathy. It may also be useful in the treatment of burning mouth syndrome. A 2004 narrative review claimed that trazodone could be used in the treatment of complex regional pain syndrome. Trazodone may also be effective in the treatment of functional gastrointestinal disorders. It may be effective in the treatment of non-cardiac chest pain as well.

Trazodone may be useful in promoting motor recovery after stroke.

Veterinary Use

Trazodone has been used to reduce anxiety and stress, to improve sleep, and to produce sedation in dogs and cats in veterinary medicine.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Trazodone >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is a Norapinephrine-Dopamine Disinhibitor?

Published on by Andrew MarshallLeave a comment

Introduction

Norepinephrine and dopamine disinhibitors (NDDIs) are a class of drugs which act at specific sites to disinhibit downstream norepinephrine and dopamine release in the brain.

Outline

Agomelatine, an antidepressant which disinhibits norepinephrine and dopamine release in the frontal cortex by antagonising 5-HT2C receptors, was the first drug to be described as an NDDI. While many other drugs also antagonise 5-HT2C receptors to some degree or another, they tend to be very non-specific in their actions, and as a result, the term “NDDI” has generally, though not always (for instance, fluoxetine has been called an NDDI in addition to SSRI due to its (weak) blockade of 5-HT2C), been reserved for describing newer, more selective agents in which disinhibition of norepinephrine and dopamine release is their primary mechanism of action.

Another drug that has been referred to as an NDDI in the medical literature is flibanserin, which is approved as a treatment for hypoactive sexual desire disorder in premenopausal women. Flibanserin disinhibits norepinephrine and dopamine release in the prefrontal cortex by activating 5-HT1A receptors in this area.

Aside from agomelatine, fluoxetine, flibanserin and mirtazapine, as of present, no other drugs have been described as NDDIs in the medical literature, despite the fact that many other existing drugs possess effects consistent with those of the definition of an NDDI. In any case, more drugs labelled specifically as NDDIs may be seen in the future.

Refer To

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Norepinephrine-dopamine_disinhibitor >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is an Noradrenergic and Specific Serotonergic Antidepressant?

Published on by Andrew Marshall4 Comments

Introduction

Noradrenergic and specific serotonergic antidepressants (NaSSAs) are a class of psychiatric drugs used primarily as antidepressants.

They act by antagonizing the α2-adrenergic receptor and certain serotonin receptors such as 5-HT2A and 5-HT2C, but also 5-HT3, 5-HT6, and/or 5-HT7 in some cases. By blocking α2-adrenergic autoreceptors and heteroreceptors, NaSSAs enhance adrenergic and serotonergic neurotransmission in the brain involved in mood regulation, notably 5-HT1A-mediated transmission. In addition, due to their blockade of certain serotonin receptors, serotonergic neurotransmission is not facilitated in unwanted areas, which prevents the incidence of many side effects often associated with selective serotonin reuptake inhibitor (SSRI) antidepressants; hence, in part, the “specific serotonergic” label of NaSSAs.

List of NaSSAs

The NaSSAs include the following agents:

  • Aptazapine (CGS-7525A)
  • Esmirtazapine (ORG-50,081)
  • Mianserin (Bolvidon, Norval, Tolvon)
  • Mirtazapine (Norset, Remeron, Avanza, Zispin)
  • Setiptiline/teciptiline (Tecipul)

Notably, all of these compounds are analogues and are also classified as tetracyclic antidepressants (TeCAs) based on their chemical structures.

S32212, a structurally novel NaSSA with an improved selectivity profile (e.g., no antihistamine effects, etc.), was reported in 2012. It has completed preliminary preclinical research and may go on to undergo clinical trials.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Noradrenergic_and_specific_serotonergic_antidepressant >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is Hydrazine?

Published on by Andrew MarshallLeave a comment

Introduction

The hydrazine antidepressants are a group of non-selective, irreversible monoamine oxidase inhibitors (MAOIs) which were discovered and initially marketed in the 1950s and 1960s. Most have been withdrawn due to toxicity, namely hepatotoxicity, but a few still remain in clinical use.

Tranylcypromine, a structurally unrelated MAOI introduced around the same time as the hydrazines, was originally advertised as non-hydrazine as a result of its diminished propensity for causing hepatotoxicity.

List of Hydrazine Antidepressants

  • Marketed:
    • Benmoxin (Neuralex, Nerusil) ‡
    • Iproclozide (Sursum) ‡
    • Iproniazid (Marsilid) ‡
    • Isocarboxazid (Marplan)
    • Mebanazine (Actomol) ‡
    • Nialamide (Niamid) ‡
    • Octamoxin (Ximaol, Nimaol) ‡
    • Phenelzine (Nardil)
    • Pheniprazine (Catron) ‡
    • Phenoxypropazine (Drazine) ‡
    • Pivhydrazine (Tersavid) ‡
    • Safrazine (Safra) ‡
  • Legend: ‡ = Withdrawn from the market; † = Partially discontinued; Bolded names indicate major drugs.
  • Never marketed:
    • Carbenzide
    • Cimemoxin
    • Domoxin
    • Metfendrazine
  • Parkinson’s:
    • Carbidopa
  • Tranquillosedative:
    • Centazolone

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Hydrazine_(antidepressant) >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is Clovoxamine?

Published on by Andrew MarshallLeave a comment

Introduction

Clovoxamine (INN) (developmental code name DU-23811) is a drug that was discovered in the 1970s.

Outline

It was subsequently investigated as an antidepressant and anxiolytic agent but was never marketed.

It acts as a serotonin-norepinephrine reuptake inhibitor (SNRI), with little affinity for the muscarinic acetylcholine, histamine, adrenergic, and serotonin receptors.

The compound is structurally related to fluvoxamine.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Clovoxamine >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.

What is Buprenorphine/Samidorphan?

Published on by Andrew MarshallLeave a comment

Introduction

Buprenorphine/samidorphan (developmental code name ALKS-5461) is a combination formulation of buprenorphine and samidorphan which is under development as an add on to antidepressants in treatment-resistant depression (TRD).

ALKS-5461 failed to meet its primary efficacy endpoints in two trials from 2016. On the basis of a third study that did meet its primary endpoints, Alkermes initiated a rolling New Drug Application with the FDA.

In November 2018, a US Food and Drug Administration (FDA) panel voted against recommending approval, finding that evidence was insufficient. As such, approval of the medication was rejected in 2019. It is a κ-opioid receptor (KOR) antagonist and is being developed by Alkermes.

Brief History

ALKS-5461 was granted Fast Track Designation by the FDA for treatment-resistant depression in October 2013. During June and July 2014, three phase III clinical trials were initiated in the United States for treatment-resistant depression. Alkermes reported that the first two trials failed in 2016. In August 2017, based on the third trial, Alkermes announced the initiation of a rolling submission of a New Drug Application for ALKS-5461 to the FDA. On 31 January 2018, Alkermes submitted a New Drug Application for ALKS-5461 to the FDA for the adjunctive treatment of major depressive disorder. The submission was accepted by the FDA on 09 April 2018 after initially serving a refuse-to-file letter due to insufficient evidence of overall effectiveness.

In November 2018, an FDA advisory committee voted 21-2 against recommending approval of ALKS-5461 for MDD, setting the medication up for likely rejection. The main reason cited was insufficient evidence of effectiveness. The panel voted in favour of adequate safety having been demonstrated.

Pharmacology

Pharmacodynamics

ALKS-5461 is a (1:1 ratio) combination of:

  1. Buprenorphine, a weak partial agonist of the μ-opioid receptor (MOR), antagonist/very weak partial agonist of the κ-opioid receptor (KOR), and, to a lesser extent, antagonist of the δ-opioid receptor (DOR) and weak partial agonist of the nociceptin receptor (NOP); and
  2. Samidorphan, a preferential antagonist of the MOR (but also, to a slightly lesser extent, weak partial agonist of the KOR and DOR).

The combination of these two drugs putatively results in what is functionally a blockade of KORs with negligible activation of MORs.

κ-Opioid Receptor Antagonism

It has been known since the 1980s that buprenorphine binds to at high affinity and antagonizes the KOR.

Through activation of the KOR, dynorphins, opioid peptides that are the endogenous ligands of the KOR and that can, in many regards, be figuratively thought of as functional inverses of the morphine-like, euphoric and stress-inhibiting endorphins, induce dysphoria and stress-like responses in both animals and humans, as well as psychotomimetic effects in humans, and are thought to be essential for the mediation of the dysphoric aspects of stress. In addition, dynorphins are believed to be critically involved in producing the changes in neuroplasticity evoked by chronic stress that lead to the development of depressive and anxiety disorders, increased drug-seeking behaviour, and dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. In support of this, in knockout mice lacking the genes encoding the KOR and/or prodynorphin (the endogenous precursor of the dynorphins), many of the usual effects of exposure to chronic stress are completely absent, such as increased immobility in the forced swimming test (a widely employed assay of depressive-like behaviour) and increased conditioned place preference for cocaine (a measure of the rewarding properties and addictive susceptibility to cocaine). Accordingly, KOR antagonists show robust efficacy in animal models of depression, anxiety, anhedonia, drug addiction, and other stress-related behavioural and physiological abnormalities.

A mouse study found that knockout of the MOR or DOR or selective pharmacological ablation of the NOP did not affect the antidepressant-like effects of buprenorphine, whereas knockout of the KOR abolished the antidepressant-like effects of the drug, supporting the notion that the antidepressant-like effects of buprenorphine are indeed mediated by modulation of the KOR by the drug (and not of the MOR, DOR, or NOP). However, a subsequent study found that the MOR may play an important role in the antidepressant-like effects of buprenorphine in animals.

Buprenorphine is not a silent antagonist of the KOR but rather a weak partial agonist. In vitro, it has shown some activation of the KOR at concentrations of ≥ 100 nM, with an Emax of 22% at 30 μM; no plateau in maximal response (EC50) was observed at concentrations up to 30 μM. Samidorphan similarly shows activation of the KOR in vitro, but to an even greater extent, with an EC50 of 3.3 nM and an Emax of 36%. As such, ALKS-5461 may possess both antagonistic and agonistic potential at the KOR. Because antagonism of the KOR seems to be responsible for the antidepressant effects of ALKS-5461, this property could in theory limit the effectiveness of ALKS-5461 in the treatment of depression.

This page is based on the copyrighted Wikipedia article < https://en.wikipedia.org/wiki/Buprenorphine/samidorphan >; it is used under the Creative Commons Attribution-ShareAlike 3.0 Unported License (CC-BY-SA). You may redistribute it, verbatim or modified, providing that you comply with the terms of the CC-BY-SA.