`El REVIEW ARTICLE
`
`A Review of Vilazodone, Serotonin,
`and Major Depressive Disorder
`
`Kerri A. Pierz, PhD, and Michael E. Thase, MD
`
`This work may not be copied, distributed,
`displayed, published, reproduced,
`transmitted, modified, posted, sold,
`licensed, or used for commercial purposes.
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`to the publisher’s Terms & Conditions.
`
`ABSTRACT
`
`Objective: To review the mechanism of selective
`serotonin reuptake inhibitor (SSRI)—mediated
`serotonergic neurotransmission, focusing on
`serotonin 1A (S—HT, A) autoreceptors, which are
`proposed to be involved in delaying therapeutic
`efficacy. Vilazodone was specifically designed to
`function both as an SSRI and a partial agonist at
`S-HT1 A receptors. This combined mechanism is
`proposed to decrease time to efficacy, minimize
`sexual side effects, and provide concomitant
`anxiolytic properties.
`
`Data Sources: A PubMed search of all English-
`language articles from January 1990 to January 2013
`was conducted using the search terms depression
`and 5—HT1A, depression and buspirone, depression and
`pindolol, and vilazodone.
`
`Study Selection: We found 47 articles and
`abstracts that were selected for inclusion on the
`basis of information about the pharmacology of
`S-HT1 A receptors and the clinical data on pindolol,
`buspirone, and Vilazodone in depression.
`Data Extraction: This review summarizes current
`
`literature involving antidepressant activity, the role
`of S—HT,A autoreceptors, and clinical trials involving
`serotonin reuptake inhibition in conjunction with
`S—HTM agonists and partial agonists, with a focus on
`vilazodone.
`
`Results: Vilazodone has demonstrated efficacy in 2
`large, randomized, double-blind, placebo—controlled
`trials in major depressive disorder. Results suggest
`that Vilazodone has a low incidence of sexual side
`effects and is effective in patients with high levels
`of anxiety. A pooled analysis shows evidence of
`significant symptom reduction after only 1 week of
`therapy.
`Conclusions: If future studies corroborate the clinical
`benefits attributed to its mechanism of action,
`Vilazodone may show potential advantages in terms
`of onset of action, sexual side effects, and anxiolytic
`activity in patients with major depressive disorder.
`
`Prim Care Companion CNS Disord
`2014,-16(1):doi:10.4088/PCC.13r01554
`© Copyright 2014 Physicians Postgraduate Press, Inc.
`
`
`Submitted: July 10, 2073; accepted October 1, 2013.
`Published online: January 9, 2014.
`Corresponding author: Kerri A. Pierz, PhD, c/o John Edwards,
`I 85 Hudson St, Plaza 5 28th Floor, Jersey City, NJ 0737 i
`(kerri.pierz@gmaiicom).
`
`Prim Care Companion CNS Disord
`2014;16(1):doi:10.4088/PCC.13r01554
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`ajor depressive disorder (MDD) is a debilitating condition with
`lifetime prevalence in the United States of 19.2%.1 The World
`Health Organization ranks MDD as the leading cause of disease burden
`in high- and middle-income countries2 and the second-leading cause of
`years lived with disability worldwide.3 Data from the 1995—1996 National
`Ambulatory Medical Care Survey demonstrated that 8% of all primary
`care office visits were depression related,4 and the role of primary care
`in treating MDD is increasing due to changes in health care coverage,
`improved depression screening tools, and the development of newer-
`generation antidepressants with improved safety profiles.“"6 Since a
`growing share of the responsibility for MDD diagnosis and treatment
`falls on primary care physicians, an understanding of the history,
`neurobiological mechanisms, and pharmacologic treatment of MDD may
`enhance patient care.
`In the 19505, the discovery of the therapeutic effects of medications
`now classified as tricyclic antidepressants (TCAs) and monoamine oxidase
`inhibitors (MAOIs) led to more widespread treatment of depression.7
`Although the antidepressant actions of the TCAs and MAOIs are likely
`to be initiated by different mechanisms, they ultimately have a similar
`effect of increasing neurotransmitter availability in the synaptic cleft.
`The TCAs inhibit reuptake of certain neurotransmitters, particularly
`norepinephrine and, for some TCAs, serotonin. The MAOIs, in contrast,
`inhibit the metabolism of serotonin, dopamine, and norepinephrine.7
`One major limiting factor in the use of these 2 drug classes is their side
`effect profiles. For example, the TCAs can produce adverse cholinergic
`and adrenergic effects, and, in excessive doses or overdoses, can cause
`seizures and potentially lethal arrhythmias.”8 The MAOIs can produce
`orthostatic hypotension and edema."'10 Moreover, because levels of the
`A form of the enzyme MAO are high in the gut and liver, inhibition of
`MAO requires dietary restrictions to reduce the risk of a serious and
`potentially fatal adverse event, hypertensive crisis. “ There was thus a clear
`motivation to develop newer, more selective antidepressant medications,
`and, by the late 19805, research led to the introduction of a new class of
`antidepressants, the selective serotonin reuptake inhibitors (SSRIs). As
`compared with the first-generation antidepressants, SSRIs were found to
`be generally similar in efficacy for the treatment of depressed outpatients,
`with a better tolerability profile.8 Moreover, the SSRIs were profoundly
`safer in overdose than the TCAs. As a result of these differences, the SSRIs
`
`rapidly supplanted the TCAs and MAOIs as the antidepressant class of
`first choice for both psychiatrists and primary care providers. Indeed, by
`the end of the first decade of the “SSRI first” era, primary care physicians
`were prescribing more antidepressants than psychiatrists.”
`Shortlyafterthe introduction ofthe SSRIs, anotherclass ofantidepressants
`known as the serotonin-norepinephrine reuptake inhibitors (SNRIs)
`was introduced. As suggested by the name, these medications inhibit the
`reuptake of norepinephrine in addition to serotonin and, as such, directly
`affect both serotonergic and noradrenergic neurotransmission. However,
`it should be noted that most of these compounds show much greater
`inhibition of serotonin reuptake than norepinephrine reuptake (10—fold
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`Pierz and Thase
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`
`
`I Vilazodone is a novel antidepressant medication that may
`offer clinical benefits with regard to onset of action and side
`effect profile.
`
`I Serotonin 1A (5-HTM) receptors have an important role in
`modulating the serotonergic system.
`
`I Drugs that target 5-HT1A receptors, particularly in
`combination with inhibition of serotonin transporters, may
`be of value in the treatment of mood disorders.
`
`for duloxetine and 30—fold for venlafaxine), such that at
`normal therapeutic doses, most of their activity very likely
`results from their serotonergic effects.”14 Although not as
`widely prescribed as the SSRIs, several SNRIs are also now
`considered to be first—line treatment options for MDD. It was
`proposed that the property of dual reuptake inhibition might
`convey an efficacy advantage for the SNRIs over SSRIs”;
`however, few studies have found large, statistically significant
`differences between the 2 drug classes, and meta-analyses
`generally document relatively small average differences
`that fall below proposed margins of clinical relevance.15‘18
`Moreover, no evidence of a difference in efficacy has been
`found in comparisons of venlafaxine and/or duloxetine
`versus the most selective SSRI, escitalopram.15"6’19 For these
`reasons, in light of the pharmacologic profile of the novel
`antidepressant Vilazodone,20 this article focuses on alternate
`serotonergic mechanisms that may be drawn upon to try to
`address the unmet needs of antidepressant therapy.
`
`METHOD
`
`A PubMed search of all English-language articles
`from January 1990 to January 2013 was conducted using
`the search terms depression and 5-HT”, depression and
`buspirone, depression and pindolol, and Vilazodone. We found
`47 articles and abstracts that were selected for inclusion
`
`on the basis of information about the pharmacology of
`serotonin (S-hydroxytryptamine) 1A (5-HT1A) receptors
`and the clinical data on pindolol, buspirone, and Vilazodone
`in depression.
`This review summarizes current literature involving
`antidepressant activity, the role of 5—HT“, autoreceptors,
`and clinical trials involving serotonin reuptake inhibition in
`conjunction with 5-HT1A agonists and partial agonists, with
`a focus on Vilazodone.
`
`THE SEROTONERGIC SYSTEM
`AND MAJOR DEPRESSIVE DISORDER
`
`Although the discovery of the first antidepressants was
`serendipitous, development of the SSRI drug class resulted
`from the deliberate and concerted efforts ofscientists working
`in drug discovery. As early as the 19603, hypotheses began to
`circulate about the role of serotonin in the pathophysiology
`of depression and as a target for antidepressant drugs.”23
`Research on the SSRIs began in the 19708, with zimelidine
`being the first such drug to reach clinical trials and fluoxetine
`becoming the first to be approved by the US Food and Drug
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`Administration (FDA) in 1987.2'24 The other SSRIs were
`subsequently introduced: paroxetine, sertraline, fluvoxamine,
`citalopram, and escitalopram.
`Serotonergic pathways in the brain all emanate from
`the raphe nuclei, branching out to nearly every region of
`the central nervous system (Figure 1). Serotonin plays
`an important role in many brain functions, including
`contributing to the regulation of mood, fear responses, sleep,
`appetite, and sexual behavior.”26 Serotonergic neurons also
`project to the hippocampus, a region in which the generation
`of new neurons (“neurogenesis”) and synaptic plasticity have
`been implicated as possible factors in the development and
`treatment of MDD.27
`
`SEROTONIN BIOCHEMISTRY
`AND PHARMACOLOGY
`
`Serotonin is a monoamine neurotransmitter that is
`
`synthesized from the amino acid tryptophan. Like tryptophan
`and the other amino acids, serotonin contains a positive and
`negative charge at physiologic pH, making it hydrophilic and
`unable to easily cross cellular membranes or the blood-brain
`barrier. This property makes it unable to diffuse back into
`neurons after its release, thereby necessitating a specific
`transport mechanism for its removal from the synaptic
`cleft. Serotonergic uptake occurs through the serotonin
`transporter (SERT), an integral membrane protein located in
`the presynaptic neuron. Thus, serotonin is transported from
`the synaptic space back into the presynaptic cell from which
`it was released (Figure 2A), where it is either repackaged
`into synaptic vesicles for subsequent re-release or degraded
`by MAO. The therapeutic efficacy of MAOIs is believed
`to be initiated by inhibiting the enzymatic degradation of
`serotonin, while the efficacy of the SSRIs is presumed to be
`initiated by inhibition of the SERT (Figure 2B, step 1).
`Once serotonin is released into the synapse, it can bind
`approximately 20 different endogenous receptor subtypes.”29
`These receptors fall into 7 distinct families based on their
`amino acid sequence, drug response, and cellular effects. In
`the serotonergic pathways that originate in the raphe nuclei,
`these serotonin receptor subtypes can be found on various
`postsynaptic, non~serotonin-containing neurons throughout
`the brain; these receptors are known as heteroreceptors (Table
`1). A few of the receptors, notably subtypes 5-HT”, 5-HTIB,
`5-HT”), and 5-HT”, are also expressed on the serotonin-
`containing raphe neurons themselves as autoreceptors, where
`they regulate further serotonin release. Generally, serotonin
`activation of autoreceptors leads to the inhibition of neuronal
`firing and serotonin release through negative feedback
`mechanisms within the raphe neuron (Table 1). The 5-HT“
`receptors are the primary 5—HT autoreceptor expressed
`on the cell body and dendrites (“somatodendritic”) of the
`raphe neurons and regulate 5—HT via modulation of action
`potential activity. The 5-HT”; receptors are the primary
`terminal autoreceptors, expressed on the axonal termini; they
`modulate 5-HT activity via inhibition of 5—HT synthesis and
`release from the raphe neurons. Finally, the 5-HT”; receptors
`have more recently been proposed as autoreceptors given
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`Prim Care Companion'CNS Disord
`2014;16(1):doi:10.4088/PCC.13r01554
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`

`

`Vilazodone, Serotonin, and Major Depressive Disorder
`
`
`Figure 1. Serotonergic Pathways and Depression—Related Symptomsa'b
`
`Striatum
`psychomotor
`
`
`
`.
`--
`Rostral
`raphe nuclei
`
`Amygdala
`suicide,
`anxiety
`
`
`
`Prefrontal cortex
`mood, suicide
`
`Nucleus
`accumbens
`anhedonia
`
`Hypothalamus
`weight loss, insomnia
`
`.'
`
`I
`
`I.-'
`
`Hippocampus
`memory
`
`_
`
`'1
`
`Caudal
`raphe nuclei
`
`3Adapted with permission from Berger et al.26
`l’All serotonin in the central nervous system is produced by neurons emanating from the raphe nuclei, which project to nearly every
`brain region. Serotonin—innervated brain structures that are closely associated with MDD are shown in bold, followed by MDD-
`related behavioral symptoms and physical effects.
`Abbreviation: MDD = major depressive disorder.
`
`apparent cross-talk with 5-HT”, receptors and modulation
`of the serotonin transporter.30 Additional investigation is
`needed to more fully understand the expression pattern and
`activity of 5-HT”; autoreceptors.
`
`5-HT” AUTORECEPTORS IN DEPRESSION
`
`A growing body of evidence suggests that 5-HT“
`receptors are involved in depression and antidepressant
`activity.28 In patients with MDD, 5—HT1A receptor expression
`and activity are altered in raphe nuclei, hippocampus,
`and many cortical regions?“34 The activation of 5-HT1 A
`autoreceptors, through the binding of serotonin (or full or
`partial receptor agonists), initially produces an inhibition
`of serotonin release by the neuron (Figure 2B, step 2).35
`However, current theory predicts that sustained, long-term
`5-HT1 A receptor stimulation soon leads to a desensitization
`and/or down-regulation of the autoreceptors so that, over
`time, serotonin release is no longer inhibited (Figure ZB,
`step 3).25 The time required for this process of inhibition
`
`Prim Care Companion CNS Disord
`2014;16(1):doi:10.4088/PCC.13r01554
`
`followed by disinhibition of the serotonergic system may
`partially explain why serotonergic antidepressant drugsss‘38
`often require several weeks or more to achieve maximal
`symptomatic improvement.
`Initially, drugs like SSRIs and SNRIs inhibit serotonin
`reuptake through SERT, producing an increase in synaptic
`serotonin, which binds postsynaptic receptors found
`proximal to the synaptic cleft to increase serotonergic
`signaling (Figure 2B, step 1). However, the increased
`serotonin also begins to bind more distal 5-HT”
`autoreceptors, for example, those found back on the
`raphe neuron cell bodies, which ultimately inhibit further
`neuronal firing and result in decreased serotonin release
`(Figure 2B, step 2). Eventually, 5-HT” autoreceptors
`desensitize or are down-regulated, removing the inhibitory
`signal and permitting synaptic serotonin levels to rise in
`the presence of sustained blockade of SERT by the SSRI
`(Figure 2B, step 3). The net result over time is the sustained
`increase of serotonergic neurotransmission made possible
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`igure 2. Effects of SSRIs and 5-HT1 A Partial Agonists on Serotonergic Transmission
`
`A. Basal Serotonergic Neurotransmission (No Drug)
`
`Semmnm
`Transporter
`
`
`
`{.
`Presynaptic Cell
`(Raphe Neuron)
`
`r.
`
`B. Effect of SSRI Treatment on Serotonergic Neurotransmission
`Step 1: Inhibition of Serotonin Reuptake by Serotonin Transporter
`
`
`
`Step 3;Bown.Regu|atii3.-;6f5-.IHT1'A Amoreceptors
`
`...................................................
`
`u C
`
`. Effect ofViIazodone on Serotonergic Neurotransmission
`
`I;
`
`VIlazodone
`\
`
`(A) Serotonin released from the presynaptic cell (orange) activates 5-HT heteroreceptors, causing a biological response in
`postsynaptic cells (indicated by +). Serotonin is removed from the synaptic cleft and other extracellular space by the serotonin
`transporter, located on the presynaptic cell. In MDD, synaptic levels of serotonin are lower than in a nondepressed state.
`(B) Effect of SSRI treatment on serotonergic neurotransmission. Step 1, immediate effects: an SSRI blocks the reuptake of serotonin
`through the serotonin transporter, increasing the levels of serotonin in the synapse and increasing the activation of nearby
`postsynaptic receptors (+). Step 2, activation of presynaptic negative feedback loop: the increase in extracellular serotonin also
`leads to stimulation of the presynaptic 5-HT“ autoreceptors, creating a negative feedback loop (—) that decreases neuronal
`activation (indicated by a smaller yellow arrow) and serotonin release (indicated by fewer serotonin molecules in the synapse).
`Step 3, long-term effects: the negative feedback pathway triggered by the activation of 5—HT” autoreceptors attenuates over time
`following the desensitization or down-regulation of 5—HT, A autoreceptors, which takes approximately a few weeks with standard
`SSRI treatment. Neuronal firing and serotonin release are then restored, while serotonin transporter reuptake remains blocked.
`(C) Vilazodone is both an SSRI and a 5-HT1 A partial agonist. As an SSRI, it blocks serotonin reuptake by the serotonin transporter
`to increase serotonin accumulation in the synapse, indirectly leading to nonspecific 5—HT receptor activation. As a 5-HT”
`partial agonist, it directly activates 5-HT” autoreceptors as well as postsynaptic heteroreceptors and may also potentially hasten
`the desensitization of the 5—HT” autoreceptors. According to this theory, the faster autoreceptor desensitization may lead to a
`more rapid onset of therapeutic efficacy.
`Abbreviations: 5—HT” = serotonin 1A, MDD = major depressive disorder, SSRI = selective serotonin reuptake inhibitor.
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`

`Vilazodone, Serotonin, and Major Depressive Disorder
`
`
`
`Table 1.Serotonin Heteroreceptors and Autoreceptorsa
`Heteroreceptors (“other” receptors)
`. Found on nonserotonergic neurons
`For example, neurons that produce and release glutamate
`(or another neurotransmitter) may express receptors for serotonin;
`such receptors would be classified as heteroreceptors
`- Include all of the known serotonin receptor subtypes
`(including those subtypes that can also be found as autoreceptors)
`. Mediate the broad and global effects of serotonin (see Figure l)
`Autoreceptors (“self” receptors)
`. Serotonin receptors located on neurons that produce serotonin
`(eg, neurons of the raphe nuclei)
`. Activation of these receptors inhibits the neuron and is generally involved in
`negative feedback loops that decrease synaptic serotonin (self—regulation)
`Exception: 5-HT23 autoreceptors are proposed to increase synaptic serotonin via
`inhibition of the serotonin transporter
`. 5-HT” autoreceptors: located on presynaptic cell bodies and dendrites
`Inhibit neuronal firing, leading to decreased serotonin release
`. 5—HT”; and 5-HT”) autoreceptors: located on presynaptic axonal termini
`Decrease the number of serotonin molecules released by the cell
`Increase serotonin transporter activity, leading to increased serotonin clearance
`. S-I-ITZB autoreceptors: proposed to also be located on presynaptic axonal termini
`Decrease serotonin transporter activity; the downstream effect is not yet known
`aBased on Carr and Lucki,28 Pytliak et a1,29 and McDevitt and Neumaier.30
`
`with buspirone augmentation of SSRIs, however,
`have shown mixed results. In patients with severe
`depression who failed to respond to fluoxetine or
`citalopram, buspirone augmentation compared
`with placebo significantly reduced Montgomery-
`Asberg Depression Rating Scale (MADRS) scores
`at endpoint; early onset of action was observed for
`augmentation with buspirone versus placebo in
`patients with less severe depression, but differences
`at endpoint were not significant.47 Conversely,
`buspirone combined with fluoxetine did not show
`faster onset or increased response rates relative to
`fluoxetine alone in patients with non—treatment-
`resistant depression.48
`In the largest depression study conducted to date,
`the Sequenced Treatment Alternatives to Relieve
`Depression (STAR*D), buspirone augmentation was
`one of multiple second-step treatment strategies in
`patients who failed to achieve remission with up to _
`14 weeks of citalopram treatment.49 In this study,”
`augmentation with buspirone was associated with a
`30% remission rate, which was similar to the rate seen with
`sustained-release bupropion augmentation.42
`Multiple double-blind trials have shown efficacy for
`pindolol augmentation of SSRIs to both hasten onset of
`therapeutic action and/or improve symptom resolution at
`endpoint.5°‘56 The effectiveness of pindolol augmentation,
`however, was not supported in other studies.57'6° Discrepant
`results may be due to differences between studies in regard
`to patient selection, study design, and pindolol dose.61
`Meta—analyses of pindolol augmentation studies suggest
`that the addition of pindolol to SSRI treatment was effective
`in accelerating the onset of clinical action, with significant
`benefits versus placebo observed in the initial weeks of
`treatment.62'63
`
`VILAZODONE
`
`Vilazodone was approved by the FDA for the treatment
`of MDD in January 2011. Pharmacologically, Vilazodone
`increases serotonin levels by inhibiting SERT, with additional
`partial agonist properties at 5-HT”, receptors.“ It has been
`hypothesized that this dual mechanism of action has the
`potential to shorten ,the onset of antidepressant activity,
`decrease side effects attributed to serotonin reuptake
`inhibition (eg, sexual dysfunction), and provide enhanced
`benefits for symptoms of anxiety.31
`As a result of the partial agonist activity at autoreceptors,
`the desensitization or down—regulation of 5-HT1A
`autoreceptors that purportedly underlies the delayed efficacy
`of SSRIs is hypothesized to occur with Vilazodone over a
`shorter period of time (Figure 2C). Studies in animal models
`support this hypothesis, as Vilazodone appears to desensitize
`5-HT“, autoreceptors more rapidly than conventional
`SSRIs.65 Additionally, Vilazodone has also been shown to
`increase serotonin levels in rat cortex and hippocampus to
`an extent greater than other SSRIs, as measured by in vivo
`microdialysis."‘5'67
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`by the removal of the 5-HT“ receptor—mediated negative
`feedback loop (“disinhibition”).
`Ligands that bind to 5-HT1A autoreceptors and
`heteroreceptors, as antagonists (which block serotonin
`activity), full agonists (which mimic serotonin activity), or
`partial agonists (which mimic and compete with serotonin
`binding, but only produce a partial response relative to
`endogenous serotonin), have shown beneficial effects
`on depression symptoms, both clinically and in research
`situations.35'37 Buspirone, a drug used to treat generalized
`anxiety disorder, is a full agonist at presynaptic 5-HT1 A
`autoreceptors, where it initially inhibits both serotonin
`synthesis and neuronal firing. Buspirone is also a partial
`agonist at 5—HT1A heteroreceptors in the hippocampus and
`frontal cortex, where it can help attenuate dysfunctional
`serotonergic transmission in MDD.35 Pindolol, a B-adrenergic
`receptor antagonist and a partial agonist of 5—HT,A receptors,
`shows similar effects.”39 Both compounds have been shown
`to enhance the effects of SSRIs, possibly by directly binding
`to 5-HT“, autoreceptors and hastening their desensitization
`and down-regulation (Figure 2B, step 3).3‘5’39‘42
`
`5-HT” AGONISTS/PARTIAL AGONISTS IN
`TREATMENT OF DEPRESSION
`
`It has been hypothesized that pharmacotherapy with
`5—HT“, agonists or partial agonists alone could be effective
`in the treatment of depression and anxiety, while avoiding
`the typical side effects of many SSRIs (eg, nausea, sexual
`dysfunction, sleep disturbances); however, the effectiveness
`of 5—HT1A agonists and partial agonists as monotherapy for
`MDD has been modest, and they are primarily used only as
`augmenting agents in combination with SSRIS.42’43
`Preliminary studies using case reports, chart reviews, and
`open-label trials suggested that buspirone augmentation was
`effective in improving depression symptoms in patients who
`were refractory to SSRI treatment.4"““5 Double-blind studies
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`Prim Care Companion CNS Disord
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`Pierz and Thase
`
`Clinical Trials of Vilazodone for MDD
`
`The clinical efficacy of Vilazodone was demonstrated
`through the results of two 8-week, phase III, randomized,
`double-blind, placebo—controlled trials“68 in adult
`outpatients diagnosed with MDD according to DSM-IV-TR
`criteria.69 In both studies, Vilazodone compared with placebo
`demonstrated statistically significant improvement on the
`primary outcome measure, change from baseline to week 8
`in MADRS7° total score, as well as on the 17-item Hamilton
`
`Depression Rating Scale (HDRS- 17) total score.71
`In the first study,68 significant improvements in MADRS
`and HDRS- 17 total scores were observed in patients treated
`with Vilazodone compared with placebo as early as week 1,
`suggesting a rapid onset of action. In the second trial,41 a
`significant difference in MADRS total score for Vilazodone
`compared with placebo was observed after 6 weeks of
`treatment, with a trend for improvement (P = .051) noted as
`early as week 4.
`These individual studies were not powered or designed
`to evaluate the clinical relevance of the effects at time
`
`points earlier than 8 weeks; however, post hoc analyses of
`the pooled data (436 Vilazodone—treated and 433 placebo-
`treated patients) indicated significant treatment differences
`favoring Vilazodone at week 1 in MADRS total score change
`from baseline, as well as in rates of response (defined as 2 50%
`improvement on the MADRS).72
`The most commonly reported adverse events that occurred
`with significantly (P<.OS) greater incidence in Vilazodone-
`treated versus placebo-treated patients were diarrhea (28.0%
`vs 9.2%, respectively), nausea (23.4% vs 5.1%, respectively),
`dizziness (8.5% vs 4.6%, respectively), insomnia (6.0% vs
`2.1%, respectively), vomiting (4.6% vs 1.2%, respectively), and
`abnormal dreams (4.1% vs 1.2%, respectively)?“73 Adherence
`to the recommended dose titration schedule (10 mg daily for
`1 week, increased to 20 mg daily for 1 week and 40 mg daily
`thereafter) is important to minimize gastrointestinal adverse
`events and to achieve the full recommended dose of 40 mg
`per day.
`Sexual dysfunction is a well-recognized side effect of some
`antidepressant drugs. However, patients often underreport
`sexual problems with the spontaneous adverse event collection
`methods used in traditional clinical trials. While most SSRI
`
`trials generally report a low incidence of sexual dysfunction
`adverse events, some studies that used specific metrics to
`evaluate sexual dysfunction have reported a significantly
`higher rate of sexual dysfunction (up to 63% and 41% of men
`and women, respectively) associated with SSRI treatment
`compared with placebo or non—SSRI antidepressants.74’75
`Therefore, it is important to include validated, standardized
`evaluations of sexual function in trials of drug classes that
`are known to affect sexual functioning to ensure that this
`important side effect is systematically assessed.
`In the phase III studies of Vilazodone, sexual function
`was evaluated using validated scales; the Arizona Sexual
`Experiences Questionnaire was used in the first study‘8 and the
`Changes in Sexual Functioning Questionnaire was used in the
`second study.41 Changes in sexual function, as reported using
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`these measures, were found to be minimal over the 8-week
`
`treatment period in the Vilazodone group and were generally
`similar to placebo,76 although these studies did not include
`an active SSRI comparator and were not specifically designed
`to test for differences in sexual functioning. It is hypothesized
`that treatment-emergent sexual dysfunction was minimized
`due to the partial agonist activity of Vilazodone at 5-HT1A
`receptors. This hypothesis is consistent with the amelioration
`of SSRI-induced sexual dysfunction observed in studies of
`coadministration of an SSRI with 5-HT1A receptor partial
`agonists (for example, buspirone or pindolol).”80 Future
`clinical trials that include an active SSRI comparator would
`be necessary to test this hypothesis.81
`
`THE ROLE OF VILAZODONE IN CLINICAL PRACTICE
`
`The pharmacologic profile of Vilazodone may address
`several unmet needs inherent in the pharmacotherapy
`of depression. First, the proposed mechanism of action is
`consistent with a rapid onset of clinical efficacy, which is
`supported by the results of the pooled analysis suggesting
`effects of Vilazodone as early as week 1.“72 Perhaps equally
`important, Vilazodone may fill the void for a serotonergic
`antidepressant that has a low incidence of sexual side effects;
`it has been recommended that this claim be tested using a
`noninferiority trial versus placebo and including an active
`comparator known to increase the incidence of sexual
`dysfunction.81 It also remains to be seen whether patients
`who develop significant sexual side effects on other SSRIs
`can be readily switched to Vilazodone, with preservation
`of response and restoration of sexual function. If such
`advantages are confirmed, it would represent a significant
`advantage over current practice, which includes either
`switching to nonserotonergic antidepressants such as
`bupropion or adding “antidotes” such as sildenafil. Another
`unmet need for antidepressant therapy is better remediation
`of comorbid anxiety symptoms. Indeed, the negative impact
`of anxiety on treatment outcome for a range of first—line and
`second-line therapies was one of the strongest findings in the
`STAR*D study.82 Beyond the theoretical rationale underlying
`the pharmacologic effects of Vilazodone on‘ anxiety, clinical
`evidence has supported the efficacy of concomitant
`administration ofan SSRI and 5-HT1A receptor partial agonist
`(ie, buspirone or pindolol) in MDD.“2"‘3"‘7'5°’56 It is important
`to note, however, that the completed clinical trials were not
`specifically designed to assess onset of efficacy, sexual side
`effects, or efficacy in patients with concomitant anxiety, so
`future studies will be needed to confirm these proposed
`mechanism-based benefits. Furthermore, the interpretation
`of the onset of clinical efficacy is confounded by the titration
`schedule; significant effects that were observed at week 1 in
`one of the clinical studies occurred at a dose of only 10 mg/d,
`although the recommended therapeutic dose is 40 mg/d.
`
`CONCLUSIONS
`
`Vilazodone, a novel FDA-approved antidepressant, was
`specifically designed to function both as an SSRI, by inhibiting
`SERT, and as a partial agonist at 5-HT1A receptors, similar to
`
`Prim Care Companion CNS Disord
`2014;I6(1):d0i:IO.4088/PCC.I3rOI554
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`buspirone and pindolol. It has been hypothesized that this dual
`mechanism of action may shorten the onset of antidepressant
`activity, decrease side effects attributed to serotonin reuptake
`inhibition (eg, sexual dysfunction), and provide enhanced
`benefits for symptoms of anxiety. The efficacy ofvilazodone
`in MDD has been demonstrated in 2 large, randomized,
`double-blind, placebo—controlled trials,”68 in which patients
`treated with vilazodone compared with placebo-treated
`patients showed significant improvement after 8 weeks. In
`1 study, significant improvement compared with placebo
`was observed as early as week 1,68 although this rapid time
`course of efficacy remains to be validated. If clinical studies
`corroborate the theoretical advantages attributed to its dual
`mechanism of action, vilazodone may become a unique
`treatment option with a rapid onset, minimal sexual side
`effects, and anxiolytic properties.
`
`Drug names: bupropion (Wellbutrin, Aplenzin, and others), buspirone
`(BuSpar and others), citalopram (Celexa and others), duloxetine
`(Cymbalta), escitalopram (Lexapro and others), fluoxetine (Prozac and
`others), fluvoxamine (Luvox and others), paroxetine (Paxil, Pexeva, and
`others), sertraline (Zoloft and others), sildenafil (Viagra and Revatio),
`venlafaxine (Effexor and others), vilazodone (Viibryd).
`Author afiiliations: Clinical Data, Inc, New Haven, Connecticut (Dr
`Pierz), and Perelman School of Medicine, University of Pennsylvania,
`Philadelphia (Dr Thase). Dr Pierz is now with Purdue Pharma, Stamford,
`Connecticut.
`Potential conflicts ofinterest: Dr Pierz is a former employee of Forest
`Research Institute, the current sponsor ofvilazodone, and of Clinical
`Data Inc, the former sponsor of vilazodone, and has served as a
`consultant to Transgenomic Inc. Dr Thase has served as a consultant
`to or on the advisory boards of AstraZeneca, Bristol-Myers Squibb,
`Cerecor, Dey, Eli L