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Title: Thioridazine  
Author: World Heritage Encyclopedia
Language: English
Subject: Mesoridazine, Cyproheptadine, Chlorpromazine, Clorotepine, Promazine
Collection: Phenothiazines, Piperidines, Thioethers, Typical Antipsychotics
Publisher: World Heritage Encyclopedia


Systematic (IUPAC) name
Clinical data
Licence data US Daily Med:
  • AU: C
  • US: C (Risk not ruled out)
Legal status
  • Withdrawn by the manufacturer worldwide[1]
Routes of
Pharmacokinetic data
Bioavailability incomplete
Metabolism hepatic (at least partly mediated by CYP2D6)
Biological half-life 21-24 hours[2]
Excretion faeces
CAS Registry Number  Y
ATC code N05
PubChem CID:
DrugBank  Y
ChemSpider  Y
Chemical data
Formula C21H26N2S2
Molecular mass 370.577

Thioridazine (Mellaril or Melleril) is a piperidine typical antipsychotic drug belonging to the phenothiazine drug group and was previously widely used in the treatment of schizophrenia and psychosis; the branded product was withdrawn worldwide in 2005 because it caused severe cardiac arrhythmias, however, generic versions are available in the US.[1]

In older references, it is sometimes described as atypical,[3] but more recently it is usually described as typical,[4] with the term "atypical" usually reserved for agents showing D4 selectivity or serotonin antagonism. The atypicality of second generation agents is not clearly defined. Some believe it's low D2 affinity, quick dissociation, 5-HT2A receptor antagonism, or all of the above. Its perceived atypical effects (namely its comparatively low propensity for extrapyramidal side effects) are likely the result of its potent anticholinergic effects.


  • Indications 1
  • Side effects 2
  • Pharmacology 3
  • Metabolism 4
  • History 5
  • Research 6
  • References 7
  • External links 8


The drug was voluntarily discontinued by its manufacturer, Novartis, worldwide because it caused severe cardiac arrhythmias.[5][1][6][7]

Its primary use in medicine was the treatment of schizophrenia.[8] It was also tried with some success as a treatment for various psychiatric symptoms seen in people with dementia,[9] but chronic use of thioridazine and other anti-psychotics in people with dementia is not recommended.[10]

Side effects

For further information see: Phenothiazine

Thioridazine prolongs the QTc interval in a dose-dependent manner.[11] It produces significantly less extrapyramidal side effects than most first-generation antipsychotics.[12][13] Its use, along with the use of other typical antipsychotics, has been associated with degenerative retinopathies.[14] It has a higher propensity for causing anticholinergic side effects coupled with a lower propensity for causing extrapyramidal side effects and sedation than chlorpromazine, but also has a higher incidence of hypotension and cardiotoxicity.[15] It is also known to possess a relatively high liability for causing orthostatic hypotension compared to other antipsychotics. Similarly to other first-generation antipsychotics it has a relatively high liability for causing prolactin elevation. It is moderate risk for causing weight gain.[16] As with all antipsychotics thioridazine has been linked to cases of tardive dyskinesia (an often permanent neurological disorder characterised by slow, repetitive, purposeless and involuntary movements, most often of the facial muscles, that is usually brought on by years of continued treatment with antipsychotics, especially the first-generation (or typical) antipsychotics such as thioridazine) and neuroleptic malignant syndrome (a potentially fatal complication of antipsychotic treatment).[11] Blood dyscrasias such as agranulocytosis, leukopenia and neutropenia are possible with thioridazine treatment.[11]


Thioridazine has the following binding profile:[17]

Biologic Protein Binding affinity (Ki[nM]) Binding affinity of Mesoridazine (Ki [nM]) Binding affinity of Sulforidazine (Ki [nM]) Notes
DAT 1684 ND ND
5-HT1A 144.35 500 (HB) ND
5-HT1B 109 ND ND
5-HT1D 579 ND ND
5-HT1E 194 ND ND
5-HT2A 27.67 4.76 (HB) ND The ratio of 5-HT2A to D2 receptor binding is believed to dictate whether or not most antipsychotics are atypical or typical. In thioridazine's case its ratio of 5-HT2A to D2 receptor binding is below the level that's believed to be required for atypicality despite its relatively low extrapyramidal side effect liability in practice.[8]
5-HT2C 53 157 ND Believed to play a role in the weight gain-promoting effects of antipsychotics.[8]
5-HT3 >10000 ND ND
5-HT5A 364 ND ND
5-HT6 57.05 380 ND
5-HT7 99 73 (RC) ND
α1A 3.15 2 (HB) ND Likely the receptor responsible for the orthostatic hypotension known to occur in individuals on thioridazine.[8]
α1B 2.4 ND ND
α2A 134.15 1612.9 (HB) ND
α2B 341.65 ND ND
α2C 74.9 ND ND
β1 >10000 ND ND
β2 >10000 ND ND
M1 12.8 10 ND This receptor is believed to be the chief receptor responsible for the anticholinergic side effects of thioridazine (e.g. dry mouth, constipation, blurred vision, etc.). Likely plays a role in thioridazine's low extrapyramidal side effect liability as anticholinergic drugs such as benzatropine are routinely given to treat extrapyramidal side effects resulting from antipsychotic treatment.[8]
M2 286.33 15 ND
M3 29 90 ND
M4 310.33 19 ND
M5 12.67 60 ND
D1 94.5 ND ND
D2 0.4 4.3 0.25 Believed to be the receptor responsible for the therapeutic effects of antipsychotics.[8]
D3 1.5 2.6 0.7
D4 1.5 9.1 ND
D5 258 ND ND
hERG 191 ND ND Likely involved in thioridazine's cardiac effects.
H1 16.5 1.81 (HB) ND Likely responsible for the sedating effects of thioridazine.
H2 136 ND ND Regulates the release of hydrochloric acid into the stomach.
H4 2400 ND ND

Note: The Binding affinities given are towards cloned human receptors unless otherwise specified

Acronyms used
HB - Human brain receptor.
RC - Cloned rat receptor.
ND - No data.


Thioridazine is a racemic compound with two enantiomers, both of which are metabolized, according to Eap et al., by CYP2D6 into (S)- and (R)-thioridazine 2-sulfoxide, better known as mesoridazine,[18] and into (S)- and (R)-thioridazine-5-sulfoxide.[19] Mesoridazine is in turn metabolized into sulforidazine.[20] Thioridazine is an inhibitor of CYP1A2 and CYP3A2.[21]


The manufacturer Novartis/Sandoz/Wander of the brands of thioridazine, Mellaril in the USA and Canada and Melleril in Europe, discontinued the drug worldwide in June 2005.[1][5]


Thioridazine is known to kill intracellular extensively drug-resistant (XDR) Mycobacterium tuberculosis[22][23] and both inhibit MRSA directly but also increase the susceptibility of MRSA to β-lactam antibiotics at clinical concentrations.[24][25] It also appears to increase the efficacy of standard antimicrobial agents (even ones to which the strain in question is resistant) in treating XDR-tuberculosis (XDR-TB) via inhibiting bacterial efflux pumps.[23]


  1. ^ a b c d "SHARED CARE PROTOCOL Thioridazine" (PDF). NHS Lothian Joint Formulary. March 2012. 
  2. ^ Shvartsburd, A; Sajadi, C; Morton, V; Mirabi, M; Gordon, J; Smith, RC (August 1984). "Blood levels of haloperidol and thioridazine during maintenance neuroleptic treatment of schizophrenic outpatients". Journal of Clinical Psychopharmacology 4 (4): 194–198.  
  3. ^ Robertson A, MacDonald C (July 1984). "Atypical neuroleptics clozapine and thioridazine enhance amphetamine-induced stereotypy". Pharmacol. Biochem. Behav. 21 (1): 97–101.  
  4. ^ Ichikawa J, Dai J, O'Laughlin IA, Fowler WL, Meltzer HY (March 2002). "Atypical, but not typical, antipsychotic drugs increase cortical acetylcholine release without an effect in the nucleus accumbens or striatum". Neuropsychopharmacology 26 (3): 325–39.  
  5. ^ a b Purhonen, M; Koponen, H; Tiihonen, J; Tanskanen, A (November 2012). "Outcome of patients after market withdrawal of thioridazine: A retrospective analysis in a nationwide cohort". Pharmacoepidemiology and Drug Safety 21 (11): 1227–1231.  
  6. ^ "WHO Pharmaceuticals Newsletter 2005, No. 04: REGULATORY MATTERS: Thioridazine - Sale discontinued in Canada". Essential Medicines and Health Products Information Portal 4 (2) (World Health Organization). 2005. p. 5. Retrieved 28 October 2013. 
  7. ^ "Withdrawal of thioridazine" (PDF). Australian Prescriber 30 (3): 82. June 2007. 
  8. ^ a b c d e f Brunton, L. L.; Chabner, B.; Knollmann, B. C., eds. (2011).  
  9. ^ Kirchner, V; Kelly, CA; Harvey, RJ (2001). "Thioridazine for dementia". The Cochrane Database of Systematic Reviews (3): CD000464.  
  10. ^ Declercq T et al. Withdrawal versus continuation of chronic antipsychotic drugs for behavioural and psychological symptoms in older people with dementia. Cochrane Database Syst Rev. 2013 Mar 28;3:CD007726. PMID 23543555
  11. ^ a b c "THIORIDAZINE HYDROCHLORIDE tablet, film coated [Mutual Pharmaceutical]". DailyMed. Mutual Pharmaceutical. September 2010. Retrieved 28 October 2013. 
  12. ^ Fenton, M; Rathbone, J; Reilly, J; Sultana, A (July 2007). "Thioridazine for schizophrenia". The Cochrane Database of Systematic Reviews (3): CD001944.  
  13. ^ Keks, N; McGrath, J; Lambert, T; Catts, S; Vaddadi, K; Burrows, G; Varghese, F; George, T; Hustig, H; Burnett, P; et al. (November 1994). "The Australian multicentre double-blind comparative study of remoxipride and thioridazine in schizophrenia". Acta Psychiatrica Scandinavica 90 (5): 358–365.  
  14. ^ Fornaro, P; Calabria, G; Corallo, G; Picotti, GB (July 2002). "Pathogenesis of degenerative retinopathies induced by thioridazine and other antipsychotics: a dopamine hypothesis". Documenta Ophthalmologica 105 (1): 41–49.  
  15. ^ "Martindale: The Complete Drug Reference". Medicines Complete. The Pharmaceutical Press. 18 August 2010. Retrieved 28 October 2013. 
  16. ^ "Selected adverse effects of antipsychotic medications for schizophrenia". UpToDate. Wolters Kluwer Health. Retrieved 24 October 2013. 
  17. ^ Roth, BL; Driscol, J (12 January 2011). Database"i"PDSP K. Psychoactive Drug Screening Program (PDSP). University of North Carolina at Chapel Hill and the United States National Institute of Mental Health. Retrieved 28 October 2013. 
  18. ^ PubChem Substance Summary: Mesoridazine National Center for Biotechnology Information.
  19. ^ Eap CB, Guentert TW, Schaublin-Loidl M, Stabl M, Koeb L, Powell K, Baumann P (Mar 1996). "Plasma levels of the enantiomers of thioridazine, thioridazine 2-sulfoxide, thioridazine 2-sulfone, and thioridazine 5-sulfoxide in poor and extensive metabolizers of dextromethorphan and mephenytoin". Clinical Pharmacology & Therapy 59 (3): 322–31.  
  20. ^ PubChem Substance Summary: Sulforidazine National Center for Biotechnology Information.
  21. ^ Daniel WA, Syrek M, Ryłko Z, Kot M (2001). "Effects of phenothiazine neuroleptics on the rate of caffeine demethylation and hydroxylation in the rat liver" (PDF). Pol J Pharmacol 53 (6): 615–21.  
  22. ^ Amaral L, Boeree MJ, Gillespie SH, Udwadia ZF, van Soolingen D (June 2010). "Thioridazine cures extensively drug-resistant tuberculosis (XDR-TB) and the need for global trials is now!". Int. J. Antimicrob. Agents 35 (6): 524–6.  
  23. ^ a b Amaral, L; Viveiros, M (May 2012). "Why thioridazine in combination with antibiotics cures extensively drug-resistant Mycobacterium tuberculosis infections". International Journal of Antimicrobial Agents 39 (5): 376–380.  
  24. ^ Thanacoody, HKR (November 2007). "Thioridazine: resurrection as an antimicrobial agent?". British Journal of Clinical Pharmacology 64 (5): 566–574.  
  25. ^ Thorsing, M; Klitgaard, JK; Atilano, ML; Skov, MN; Kolmos, HJ; Filipe, SR; Kallipolitis, BH (May 2013). "Thioridazine Induces Major Changes in Global Gene Expression and Cell Wall Composition in Methicillin-Resistant Staphylococcus aureus USA300". PLoS One 8 (5): e64518.  

External links

  • PubChem Substance Summary: Thioridazine National Center for Biotechnology Information,.
  • Antipsychotic Mellaril Removed from Market Schizophrenia Daily News Blog.
  • U.S. National Library of Medicine: Drug Information Portal - Thioridazine
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