Thioridazine

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Thioridazine
Clinical data
AHFS/Drugs.comProfessional Drug Facts
MedlinePlusa682119
License data
Pregnancy
category
  • AU: C
Routes of
administration		Oral
Drug classTypical antipsychotic
ATC code
Legal status
Legal status
  • BR: Class C1 (Other controlled substances)[1]
  • Withdrawn by the manufacturer worldwide;[2] generic formulations are still available by prescription
Pharmacokinetic data
BioavailabilityIncomplete
MetabolismHepatic (at least partly mediated by CYP2D6)
Elimination half-life21–24 hours[3]
ExcretionFeces
Identifiers
  • 10-{2-[(RS)-1-Methylpiperidin-2-yl]ethyl}-
    2-methylsulfanylphenothiazine
JSmol)
  • S(c2cc1N(c3c(Sc1cc2)cccc3)CCC4N(C)CCCC4)C
  • InChI=1S/C21H26N2S2/c1-22-13-6-5-7-16(22)12-14-23-18-8-3-4-9-20(18)25-21-11-10-17(24-2)15-19(21)23/h3-4,8-11,15-16H,5-7,12-14H2,1-2H3 checkY
  • Key:KLBQZWRITKRQQV-UHFFFAOYSA-N checkY
  (verify)

Thioridazine (Mellaril or Melleril) is a first generation 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 The branded product was withdrawn worldwide in 2005 because it caused severe cardiac arrhythmias.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 still available in the US.[2]

Indications

Thioridazine was voluntarily discontinued by its manufacturer, Novartis, worldwide because it caused severe cardiac arrhythmias. However, generics remain on the market in some countries.[2][4][5][6]

Its primary use in medicine is for the treatment of schizophrenia.[7] It was also tried with some success as a treatment for various psychiatric symptoms seen in people with dementia,[8] but chronic use of thioridazine and other anti-psychotics in people with dementia is not recommended.[9] Generic forms of thioridazine remain on the market in a few countries, usually with restrictions due to the risk of arrhythmias. For example, in the US, it is restricted to patients who have taken at least 2 other antipsychotics that either failed or caused serious side effects. [10]

Side effects

Further information: Phenothiazine

Thioridazine prolongs the

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 is also associated with abnormal retinal pigmentation after many years of use.[17]
Thioridazine has been correlated to rare instances of clinically apparent acute cholestatic liver injury. [18]

Pharmacology

Thioridazine has the following binding profile:[19]

Biologic Protein Binding affinity (Ki[nM]) Binding affinity of Mesoridazine (Ki [nM]) Binding affinity of Sulforidazine (Ki [nM]) Notes
SERT 1259 ND ND
NET 842 ND ND
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.[7]
5-HT2C 53 157 ND Believed to play a role in the weight gain-promoting effects of antipsychotics.[7]
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.[7]
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
extrapyramidal side effects resulting from antipsychotic treatment.[7]
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.[7]
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

Metabolism

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,[20] and into (S)- and (R)-thioridazine-5-sulfoxide.[21] Mesoridazine is in turn metabolized into sulforidazine.[22] Thioridazine is an inhibitor of CYP1A2 and CYP3A4.[23]

History

The manufacturer Novartis/Sandoz/Wander of the brands of thioridazine, Mellaril in the US and Canada and Melleril in Europe, discontinued the drug worldwide in June 2005.[2][4]

Generic forms of thioridazine however remain on the market in a few countries usually with restrictions for example in the US its restricted to patients who have taken at least 2 other antipsychotics that either failed or caused serious side effects [24]

Antibiotic activity

Thioridazine is known to kill

amoebicidal medications
.

Synthesis

Note: Same sidechain used for mesoridazine and sulforidazine.

Thieme Synthesis:[29] Patent:[30] Sidechain:[31] Enantiomers:[32]

The alkylation of 2-Picoline [109-06-8] (1) with formaldehyde gives 2-Pyridineethanol [103-74-2] (2). Forming the quat salt with methyl iodide [74-88-4] leads to 2-(2-hydroxyethyl)-1-methyl-pyridinium iodide [56622-15-2] (3). Catalytic hydrogenation in the presence of hydrochloric acid leads to 2-(2-Chloroethyl)-1-Methylpiperidine [50846-01-0] (4). Alkylation of 2-Methylthiophenothiazine [7643-08-5] (5) in the presence of sodium hydride base completed the synthesis of Thioridazine (6).

References

  1. ^ 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.
  2. ^ a b c d "SHARED CARE PROTOCOL Thioridazine" (PDF). NHS Lothian Joint Formulary. March 2012. Archived from the original (PDF) on 18 May 2015.
  3. S2CID 33161119
    .
  4. ^
    S2CID 19560432
    .
  5. ^ "WHO Pharmaceuticals Newsletter 2005, No. 04: REGULATORY MATTERS: Thioridazine - Sale discontinued in Canada". Essential Medicines and Health Products Information Portal. Vol. 4, no. 2. World Health Organization. 2005. p. 5. Archived from the original on 28 May 2011. Retrieved 28 October 2013.
  6. ^ "Withdrawal of thioridazine" (PDF). Australian Prescriber. Vol. 30, no. 3. June 2007. p. 82.
  7. ^
    ISBN 978-0-07-162442-8
    .
  8. PMID 11686961
    .
  9. PMID 23543555
    .
  10. ^ "Thioridazine: MedlinePlus Drug Information". medlineplus.gov. Retrieved 7 June 2023.
  11. ^ a b c "THIORIDAZINE HYDROCHLORIDE tablet, film coated [Mutual Pharmaceutical]". DailyMed. Mutual Pharmaceutical. September 2010. Retrieved 28 October 2013.
  12. PMID 17636691
    .
  13. S2CID 40042606
    .
  14. S2CID 23618581
    .
  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. PMID 14065014
    .
  18. PMID 31643669
    .
  19. ^ Roth BL, Driscol J (12 January 2011). "PDSP Ki Database". Psychoactive Drug Screening Program (PDSP). University of North Carolina at Chapel Hill and the United States National Institute of Mental Health. Archived from the original on 8 November 2013. Retrieved 28 October 2013.
  20. ^ PubChem Substance Summary: Mesoridazine National Center for Biotechnology Information.
  21. S2CID 45135063
    .
  22. ^ PubChem Substance Summary: Sulforidazine National Center for Biotechnology Information.
  23. PMID 11985335
    .
  24. ^ "Thioridazine: MedlinePlus Drug Information". medlineplus.gov. Retrieved 7 June 2023.
  25. PMID 20188526
    .
  26. ^
    PMID 22445204
    .
  27. PMID 17764469
    .
  28. PMID 23691239
    .
  29. doi:10.1002/hlca.19580410420
    .
  30. ^ US 3239514, Renz J, Bourquin JP, "Phenothiazine derivatives substituted by a monovalent sulfur function in 3-position", issued 1966, assigned to Sandoz KK 
  31. PMID 20994984
    .
  32. doi:10.1055/s-0039-1690834
    .

Further reading

External links