Phenelzine

Phenelzine, sold under the brand name Nardil, among others, is a non-selective and irreversible monoamine oxidase inhibitor (MAOI) of the hydrazine class which is primarily used as an antidepressant and anxiolytic. Along with tranylcypromine and isocarboxazid, phenelzine is one of the few non-selective and irreversible MAOIs still in widespread clinical use.

Phenelzine
Clinical data
Trade namesNardil
AHFS/Drugs.comMonograph
MedlinePlusa682089
License data
Pregnancy
category
Routes of
administration		By mouth
ATC code
Legal status
Legal status
  • AU: S4 (Prescription only)
  • BR: Class C1 (Other controlled substances)[2]
  • US: ℞-only
  • In general: ℞ (Prescription only)
Pharmacokinetic data
MetabolismLiver
Elimination half-life11.6 hours
ExcretionUrine
Identifiers
  • 2-phenylethylhydrazine
CAS Number
PubChem CID
IUPHAR/BPS
DrugBank
ChemSpider
UNII
KEGG
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.000.108
Chemical and physical data
FormulaC8H12N2
Molar mass136.198 g·mol−1
3D model (JSmol)
Boiling point74 °C (165 °F)
  • N(N)CCc1ccccc1
  • InChI=1S/C8H12N2/c9-10-7-6-8-4-2-1-3-5-8/h1-5,10H,6-7,9H2 checkY
  • Key:RMUCZJUITONUFY-UHFFFAOYSA-N checkY
  (verify)

Synthesis of phenelzine was first described by Emil Votoček and Otakar Leminger in 1932.[3][4]

Medical uses

Phenelzine is primarily used in the treatment of major depressive disorder (MDD). Patients with depressive symptomology characterized as "atypical", "nonendogenous", and/or "neurotic" respond particularly well to phenelzine.[5] The medication is also useful in patients who do not respond favorably to first and second-line treatments for depression, or are "treatment-resistant".[6] In addition to being a recognized treatment for major depressive disorder, phenelzine is effective in treating dysthymia,[7] bipolar depression (BD),[8] panic disorder (PD),[9] social anxiety disorder,[10] bulimia,[11] post-traumatic stress disorder (PTSD),[12] and obsessive-compulsive disorder (OCD).[13][14]

Pharmacology

Pharmacodynamics

Phenelzine is a non-selective and irreversible inhibitor of the enzyme monoamine oxidase (MAO). It inhibits both of the respective isoforms of MAO, MAO-A and MAO-B, and does so almost equally, with slight preference for the former. By inhibiting MAO, phenelzine prevents the breakdown of the monoamine neurotransmitters serotonin, melatonin, norepinephrine, epinephrine, and dopamine, as well as the trace amine neuromodulators such as phenethylamine, tyramine, octopamine, and tryptamine. This leads to an increase in the extracellular concentrations of these neurochemicals and therefore an alteration in neurochemistry and neurotransmission. This action is thought to be the primary mediator in phenelzine's therapeutic benefits.

Phenelzine and its metabolites also inhibit at least two other enzymes to a lesser extent, of which are alanine transaminase (ALA-T),[15] and γ-aminobutyric acid transaminase (GABA-T),[16] the latter of which is not caused by phenelzine itself, but by a phenelzine metabolite phenylethylidenehydrazine (PEH). By inhibiting ALA-T and GABA-T, phenelzine causes an increase in the alanine and GABA levels in the brain and body. GABA is the major inhibitory neurotransmitter in the mammalian central nervous system, and is very important for the normal suppression of anxiety, stress, and depression. Phenelzine's action in increasing GABA concentrations may significantly contribute to its antidepressant, and especially, anxiolytic/antipanic properties, the latter of which have been considered superior to those of other antidepressants. As for ALA-T inhibition, though the consequences of disabling this enzyme are currently not well understood, there is some evidence to suggest that it is this action of the hydrazines (including phenelzine) which may be responsible for the occasional incidence of hepatitis and liver failure.

Phenelzine has also been shown to metabolize to phenethylamine (PEA).[17] PEA acts as a releasing agent of norepinephrine and dopamine, which occurs in a similar manner to amphetamine by being taken up into vesicles, displacing and causing the release of those monoamines (though with markedly different pharmacokinetics such as a far shorter duration of action). Although this is indeed the same mechanism to which some (but not all) of amphetamine's effects are attributable to, this is not all that uncommon a property among phenethylamines in general, many of which do not have psychoactive properties comparable to amphetamine. Amphetamine is different in that it binds with high affinity to the reuptake pumps of dopamine, norepinephrine, and serotonin, which phenethylamine and related molecules may as well to some extent, but with far less potency, such that it is basically insignificant in comparison. And, often being metabolized too quickly or not having the solubility to enable it to have a psychostimulant effect in humans. Claims that phenethylamine has comparable or roughly similar effects to psychostimulants such as amphetamine when administered are misconstrued. Phenethylamine does not have any obvious, easily discernible, reliably induced effects when administered to humans. Phenelzine's enhancement of PEA levels may contribute further to its overall antidepressant effects to some degree. In addition, phenethylamine is a substrate for MAO-B, and treatment with MAOIs that inhibit MAO-B such as phenelzine have been shown to consistently and significantly elevate its concentrations.

Like many other antidepressants, phenelzine usually requires several weeks of treatment to achieve full therapeutic effects. The reason for this delay is not fully understood, but it is believed to be due to many factors, including achieving steady-state levels of MAO inhibition and the resulting adaptations in mean neurotransmitter levels, the possibility of necessary desensitization of autoreceptors which normally inhibit the release of neurotransmitters like serotonin and dopamine, and also the upregulation of enzymes such as serotonin N-acetyltransferase. Typically, a therapeutic response to MAOIs is associated with an inhibition of at least 80-85% of monoamine oxidase activity.[18]

Pharmacokinetics
Phenelzine 15 mg tablets.

Phenelzine is administered orally in the form of phenelzine sulfate and is rapidly absorbed from the gastrointestinal tract. Time to peak plasma concentration is 43 minutes and half-life is 11.6 hours. Unlike most other drugs, phenelzine irreversibly disables MAO, and as a result, it does not necessarily need to be present in the blood at all times for its effects to be sustained. Because of this, upon phenelzine treatment being ceased, its effects typically do not actually wear off until the body replenishes its enzyme stores, a process which can take as long as 2–3 weeks.

Phenelzine is metabolized primarily in the liver and its metabolites are excreted in the urine. Oxidation is the primary routine of metabolism, and the major metabolites are phenylacetic acid and parahydroxyphenylacetic acid, recovered as about 73% of the excreted dose of phenelzine in the urine over the course of 96 hours after single doses. Acetylation to N2-acetylphenelzine is a minor pathway. Phenelzine may also interact with cytochrome P450 enzymes, inactivating these enzymes through formation of a heme adduct. Two other minor metabolites of phenelzine, as mentioned above, include phenylethylidenehydrazine and phenethylamine.

Adverse effects

Common side effects of phenelzine may include dizziness, blurry vision, dry mouth, headache, lethargy, sedation, somnolence, insomnia, anorexia, weight gain or loss, nausea and vomiting, diarrhea, constipation, urinary retention, mydriasis, muscle tremors, hyperthermia, sweating, hypertension or hypotension, orthostatic hypotension, paresthesia, hepatitis, and sexual dysfunction (consisting of loss of libido and anorgasmia). Rare side effects usually only seen in susceptible individuals may include hypomania or mania, psychosis and acute liver failure, the last of which is usually only seen in people with pre-existing liver damage, old age, long-term effects of alcohol consumption, or viral infection.[19]

Interactions
See also: Monoamine oxidase inhibitor § Dangers
See also: Foods containing tyramine

The MAOIs have certain dietary restrictions and drug interactions. Hypertensive crisis may result from the overconsumption of tyramine-containing foods, although it is a rare occurrence.[20][21] Serotonin syndrome may result from an interaction with certain drugs which increase serotonin activity such as selective serotonin reuptake inhibitors, serotonin releasing agents, and serotonin agonists.

Phenelzine has also been linked to vitamin B6 deficiency.[22] Transaminases such as GABA-transaminase have been shown to be dependent upon vitamin B6[23] and may be involved in a potentially related process, since the phenelzine metabolite phenylethylidenehydrazine (PEH) is a GABA transaminase inhibitor. Both phenelzine and vitamin B6 are rendered inactive upon these reactions occurring. The pyridoxine form of B6 is recommended for supplementation, since this form has been shown to reduce hydrazine toxicity from phenelzine and, in contrast, the pyridoxal form has been shown to increase the toxicity of hydrazines.[24]

Research

Phenelzine showed promise in a phase II clinical trial from March 2020 in treating prostate cancer.[25] Phenelzine has also been shown to have neuroprotective effects in animal models.[26][27][28]

References
  1. "Phenelzine (Nardil) Use During Pregnancy". Drugs.com. 3 March 2020. Retrieved 11 July 2020.
  2. Anvisa (31 March 2023). "RDC Nº 784 - Listas de Substâncias Entorpecentes, Psicotrópicas, Precursoras e Outras sob Controle Especial" [Collegiate Board Resolution No. 784 - Lists of Narcotic, Psychotropic, Precursor, and Other Substances under Special Control] (in Brazilian Portuguese). Diário Oficial da União (published 4 April 2023). Archived from the original on 3 August 2023. Retrieved 16 August 2023.
  3. Budavari S, O'Neil, Smith A, Heckelman PE, Kinneary JF (1996). "Phenelzine". The Merck Index (12th ed.). Whitehouse Station: Merck & Co. 7181.
  4. Votoček E, Leminger O (1932). "Sur la β-phenoéthylhydrazine" [On the [preparation and properties of] β-phenoethylhydrazine]. Collection of Czechoslovak Chemical Communications (in French). 4: 271–281. doi:10.1135/cccc19320271.
  5. Parke-Davis Division of Pfizer Inc. (2007). "Nardil(R) (Phenelzine sulfate tablets, USP), labeling information" (PDF). U.S. Food and Drug Administration's. Archived (PDF) from the original on 27 November 2009. Retrieved 14 December 2009.
  6. Fiedorowicz JG, Swartz KL (July 2004). "The role of monoamine oxidase inhibitors in current psychiatric practice". Journal of Psychiatric Practice. 10 (4): 239–248. doi:10.1097/00131746-200407000-00005. PMC 2075358. PMID 15552546.
  7. Vallejo J, Gasto C, Catalan R, Salamero M (November 1987). "Double-blind study of imipramine versus phenelzine in Melancholias and Dysthymic Disorders". The British Journal of Psychiatry. 151 (5): 639–642. doi:10.1192/bjp.151.5.639. PMID 3446308. S2CID 145651628.
  8. Quitkin FM, McGrath P, Liebowitz MR, Stewart J, Howard A (March 1981). "Monoamine oxidase inhibitors in bipolar endogenous depressives". Journal of Clinical Psychopharmacology. 1 (2): 70–74. doi:10.1097/00004714-198103000-00005. PMID 7028797. S2CID 32909169.
  9. Buigues J, Vallejo J (February 1987). "Therapeutic response to phenelzine in patients with panic disorder and agoraphobia with panic attacks". The Journal of Clinical Psychiatry. 48 (2): 55–59. PMID 3542985.
  10. Blanco C, Schneier FR, Schmidt A, Blanco-Jerez CR, Marshall RD, Sánchez-Lacay A, et al. (2003). "Pharmacological treatment of social anxiety disorder: a meta-analysis". Depression and Anxiety. 18 (1): 29–40. doi:10.1002/da.10096. PMID 12900950. S2CID 12296484.
  11. Walsh BT, Gladis M, Roose SP, Stewart JW, Stetner F, Glassman AH (May 1988). "Phenelzine vs placebo in 50 patients with bulimia". Archives of General Psychiatry. 45 (5): 471–475. doi:10.1001/archpsyc.1988.01800290091011. PMID 3282482.
  12. Frank JB, Kosten TR, Giller EL, Dan E (October 1988). "A randomized clinical trial of phenelzine and imipramine for posttraumatic stress disorder". The American Journal of Psychiatry. 145 (10): 1289–1291. doi:10.1176/ajp.145.10.1289. PMID 3048121.
  13. Vallejo J, Olivares J, Marcos T, Bulbena A, Menchón JM (November 1992). "Clomipramine versus phenelzine in obsessive-compulsive disorder. A controlled clinical trial". The British Journal of Psychiatry. 161 (5): 665–670. doi:10.1192/bjp.161.5.665. PMID 1422616. S2CID 36232956.
  14. Grant JE, Baldwin DS, Chamberlain SR (July 2021). "Time to Reconsider Monoamine Oxidase Inhibitors for Obsessive Compulsive Disorder?: A Case Series Using Phenelzine". Journal of Clinical Psychopharmacology. 41 (4): 461–464. doi:10.1097/JCP.0000000000001418. PMID 34108430. S2CID 235395484.
  15. Tanay VA, Parent MB, Wong JT, Paslawski T, Martin IL, Baker GB (August 2001). "Effects of the antidepressant/antipanic drug phenelzine on alanine and alanine transaminase in rat brain". Cellular and Molecular Neurobiology. 21 (4): 325–339. doi:10.1023/A:1012697904299. PMID 11775064. S2CID 20655821.
  16. McKenna KF, McManus DJ, Baker GB, Coutts RT (1994). "Chronic administration of the antidepressant phenelzine and its N-acetyl analogue: effects on GABAergic function". Journal of Neural Transmission. Supplementum. 41: 115–122. doi:10.1007/978-3-7091-9324-2_15. ISBN 978-3-211-82521-1. PMID 7931216.
  17. Dyck LE, Durden DA, Boulton AA (June 1985). "Formation of beta-phenylethylamine from the antidepressant, beta-phenylethylhydrazine". Biochemical Pharmacology. 34 (11): 1925–1929. doi:10.1016/0006-2952(85)90310-7. PMID 4004908.
  18. Raft D, Davidson J, Wasik J, Mattox A (1981). "Relationship between response to phenelzine and MAO inhibition in a clinical trial of phenelzine, amitriptyline and placebo". Neuropsychobiology. 7 (3): 122–126. doi:10.1159/000117841. PMID 7231652.
  19. Gómez-Gil E, Salmerón JM, Mas A (April 1996). "Phenelzine-induced fulminant hepatic failure". Annals of Internal Medicine. 124 (7): 692–693. doi:10.7326/0003-4819-124-7-199604010-00014. PMID 8607601. S2CID 43020372.
  20. Gillman PK (January 2019). "The risk of harm from acute tyramine-induced hypertension: how significant?". PsychoTropical Commentaries. 5: 1–10. doi:10.13140/RG.2.2.11909.40165. Archived from the original on 8 January 2022. Retrieved 8 January 2022.
  21. Grady MM, Stahl SM (March 2012). "Practical guide for prescribing MAOIs: debunking myths and removing barriers". CNS Spectrums. 17 (1): 2–10. doi:10.1017/S109285291200003X. PMID 22790112. S2CID 206312008.
  22. Malcolm DE, Yu PH, Bowen RC, O'Donovan C, Hawkes J, Hussein M (November 1994). "Phenelzine reduces plasma vitamin B6". Journal of Psychiatry & Neuroscience. 19 (5): 332–334. PMC 1188621. PMID 7803366.
  23. PDB: 1OHW​; Storici P, De Biase D, Bossa F, Bruno S, Mozzarelli A, Peneff C, et al. (January 2004). "Structures of gamma-aminobutyric acid (GABA) aminotransferase, a pyridoxal 5'-phosphate, and [2Fe-2S] cluster-containing enzyme, complexed with gamma-ethynyl-GABA and with the antiepilepsy drug vigabatrin". The Journal of Biological Chemistry. 279 (1): 363–373. doi:10.1074/jbc.M305884200. PMID 14534310.{{cite journal}}: CS1 maint: overridden setting (link)
  24. Dubnick B, Leeson GA, Scott CC (July 1960). "Effect of forms of vitamin B6 on acute toxicity of hydrazines". Toxicology and Applied Pharmacology. 2 (4): 403–409. doi:10.1016/0041-008X(60)90007-7. PMID 13818307.
  25. Stone L (April 2020). "MAOA inhibitor phenelzine efficacious in recurrent prostate cancer". Nature Reviews. Urology. 17 (4): 192. doi:10.1038/s41585-020-0307-y. PMID 32203303. S2CID 212681980.
  26. Baker G, Matveychuk D, MacKenzie EM, Holt A, Wang Y, Kar S (May 2019). "Attenuation of the effects of oxidative stress by the MAO-inhibiting antidepressant and carbonyl scavenger phenelzine". Chemico-Biological Interactions. 304: 139–147. doi:10.1016/j.cbi.2019.03.003. PMID 30857888. S2CID 75140657.
  27. Matveychuk D, MacKenzie EM, Kumpula D, Song MS, Holt A, Kar S, et al. (January 2022). "Overview of the Neuroprotective Effects of the MAO-Inhibiting Antidepressant Phenelzine". Cellular and Molecular Neurobiology. 42 (1): 225–242. doi:10.1007/s10571-021-01078-3. PMC 8732914. PMID 33839994. S2CID 233211407.{{cite journal}}: CS1 maint: overridden setting (link)
  28. Cebak JE, Singh IN, Hill RL, Wang JA, Hall ED (April 2017). "Phenelzine Protects Brain Mitochondrial Function In Vitro and In Vivo following Traumatic Brain Injury by Scavenging the Reactive Carbonyls 4-Hydroxynonenal and Acrolein Leading to Cortical Histological Neuroprotection". Journal of Neurotrauma. 34 (7): 1302–1317. doi:10.1089/neu.2016.4624. PMC 5385448. PMID 27750484.
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