Pharmacology  ·  CNS

Newer Antidepressants with Novel Mechanisms

Module 5 — Chapter 17: Antidepressant Drugs

Abbreviations: SERT = serotonin transporter  ·  SARI = serotonin antagonist and reuptake inhibitor  ·  SPARI = serotonin partial agonist and reuptake inhibitor  ·  5-HT1A = serotonin type 1A receptor  ·  5-HT2C = serotonin type 2C receptor  ·  5-HT3 = serotonin type 3 receptor  ·  5-HT7 = serotonin type 7 receptor  ·  MT1/MT2 = melatonin receptors types 1 and 2  ·  NMDA = N-methyl-D-aspartate  ·  TRD = treatment-resistant depression  ·  MDD = major depressive disorder  ·  LFT = liver function test  ·  REMS = Risk Evaluation and Mitigation Strategy

Multimodal Serotonergic Agents
Multimodal Serotonergic Antidepressant
Vortioxetine
  • SERT inhibition (primary) + 5-HT1A agonism + 5-HT3 and 5-HT7 antagonism
  • Broader serotonin network modulation than SSRIs alone
  • Cognitive benefit: improved memory and processing speed in depression trials
  • Lower sexual dysfunction than SSRIs
  • No significant drug interactions beyond MAOIs
Serotonin Partial Agonist Reuptake Inhibitor (SPARI)
Vilazodone
  • SERT inhibition + 5-HT1A partial agonism
  • Partial agonism reduces somatodendritic autoreceptor suppression
  • Lower sexual dysfunction than SSRIs
  • Must be taken with food (bioavailability doubles)
  • CYP3A4 substrate — dosing adjustment with strong inhibitors
Serotonin Antagonist and Reuptake Inhibitors (SARI)
Widely Used — Low-Dose Sedative
Trazodone
  • SERT inhibition + 5-HT2A antagonism + H1 and alpha-1 blockade
  • Antidepressant at 300–600 mg; sedative at 50–100 mg (off-label insomnia)
  • No anticholinergic effects; no sexual dysfunction
  • Priapism: rare but serious — counsel male patients
  • Orthostatic hypotension prominent
Withdrawn — Hepatotoxicity
Nefazodone
  • Similar mechanism to trazodone plus CYP3A4 inhibition
  • No sexual dysfunction; less sedation than trazodone
  • Withdrawn from most markets (Canada, Europe) due to rare but fatal hepatic failure
  • Remains available in US with black box warning
  • Monitor LFTs; discontinue if transaminases elevated
Circadian and Glutamate Mechanisms
Melatonin Receptor Agonist + 5-HT2C Antagonist
Agomelatine
  • MT1/MT2 agonism: resets circadian rhythm disruption in depression
  • 5-HT2C antagonism: disinhibits dopamine and norepinephrine in prefrontal cortex
  • No monoamine reuptake inhibition — no sexual dysfunction, no discontinuation syndrome
  • Hepatotoxicity: mandatory LFT at baseline, 3, 6, 12, 24 weeks
  • Not available in US; widely used in Europe
NMDA Receptor Antagonist — Intranasal
Esketamine (Spravato)
  • S-enantiomer of ketamine; blocks NMDA glutamate receptors
  • Rapid antidepressant effect within hours to days
  • Approved: treatment-resistant depression + oral antidepressant; major depressive disorder with acute suicidal ideation
  • REMS program: healthcare setting only; 2-hour post-dose monitoring; no home use
  • Dissociation, dizziness, nausea during administration; potential for abuse
  • No driving on day of administration
Key Safety Distinctions

Agomelatine: only antidepressant requiring scheduled LFT monitoring — do not start in active liver disease. Nefazodone: black box hepatotoxicity — use only when benefit clearly outweighs risk. Esketamine: only antidepressant with a REMS program — cannot be dispensed for home use under any circumstances.

Suggested References

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Brunton LL, Knollmann BC, eds.Goodman & Gilman's The Pharmacological Basis of Therapeutics. 14th ed.McGraw-Hill; 2023
Bang-Andersen B, Ruhland T, Jorgensen M, et al.Discovery of 1-[2-(2,4-dimethylphenylsulfanyl)phenyl]piperazine (Lu AA21004): a novel multimodal compound for the treatment of major depressive disorder.J Med Chem. 2011;54(9):3206–3221
McIntyre RS, Lophaven S, Olsen CK.A randomized, double-blind, placebo-controlled study of vortioxetine on cognitive function in depressed adults.Int J Neuropsychopharmacol. 2014;17(10):1557–1567
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Fagiolini A, Comandini A, Catena Dell'Osso M, Kasper S.Rediscovering trazodone for the treatment of major depressive disorder.CNS Drugs. 2012;26(12):1033–1049
Choi S.Nefazodone (Serzone) withdrawn because of hepatotoxicity.CMAJ. 2003;169(11):1187
Millan MJ, Gobert A, Lejeune F, et al.The novel melatonin agonist agomelatine (S20098) is an antagonist at 5-hydroxytryptamine2C receptors, blockade of which enhances the activity of frontocortical dopaminergic and adrenergic pathways.J Pharmacol Exp Ther. 2003;306(3):954–964
Kasper S, Hajak G, Wulff K, et al.Efficacy of the novel antidepressant agomelatine on the circadian rest-activity cycle and depressive and anxiety symptoms in patients with major depressive disorder.J Clin Psychiatry. 2010;71(2):109–120
U.S. Food and Drug Administration.Trintellix (vortioxetine) prescribing information. Revised 2023.FDA; 2023
Stahl SM.Stahl's Essential Psychopharmacology: Neuroscientific Basis and Practical Applications, 5th ed. Chapter 7.Cambridge University Press; 2021