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Title: Clioquinol  
Author: World Heritage Encyclopedia
Language: English
Subject: ATC code D09, 8-Hydroxyquinoline, Chloramphenicol, Benzalkonium chloride, Metronidazole
Collection: Antifungals, Antiprotozoal Agents, Chloroarenes, Iodoarenes, Organochlorides, Organoiodides, Otologicals, Quinolinols
Publisher: World Heritage Encyclopedia


Skeletal formula of clioquinol
Ball-and-stick model of the clioquinol molecule
Systematic (IUPAC) name
Clinical data
  • US: C (Risk not ruled out) [1]
Legal status
Routes of
topical only
CAS Registry Number  Y
ATC code D08
D09 (dressing) G01 P01 S02
PubChem CID:
DrugBank  Y
ChemSpider  Y
Chemical data
Formula C9H5ClINO
Molecular mass 305.50 g·mol−1

Clioquinol (iodochlorhydroxyquin) is an antifungal drug and antiprotozoal drug. It is neurotoxic in large doses. It is a member of a family of drugs called hydroxyquinolines which inhibit certain enzymes related to DNA replication. The drugs have been found to have activity against both viral and protozoal infections.[2]


  • Antiprotozoal use 1
  • Clioquinol and SMON 2
  • Topical use 3
  • Use in neurodegenerative diseases 4
  • Use for autism 5
  • Continued use and manufacture around the world 6
  • See also 7
  • References 8

Antiprotozoal use

A 1964 report described the use of Clioquinol in both the treatment and prevention of shigella infection and Entamoeba histolytica infection in institutionalized individuals at Sonoma State Hospital in California. The report indicates 4000 individuals were treated over a 4-year period with few side effects.[3]

Several recently reported journal articles describing its use as an antiprotozoal include:

  • A 2004 reference to its use in the Netherlands in the treatment of Dientamoeba fragilis infection.[5]

Clioquinol and SMON

Clioquinol's use as an antiprotozoal drug has been restricted or discontinued in some countries due to an event in Japan where over 10,000 people developed SMON (subacute myelo-optic neuropathy) between 1957 and 1970. The drug was used widely in many countries before and after the SMON event without similar reports.[7] As yet, no explanation exists as to why it produced this reaction, and some researchers have questioned whether clioquinol was the causative agent in the disease, noting that the drug had been used for 20 years prior to the epidemic without incident, and that the SMON cases began to reduce in number prior to the discontinuation of the drug.[8] Theories suggested have included improper dosing, the permitted use of the drug for extended periods of time,[9] and dosing which did not consider the smaller average stature of Japanese; however a dose dependant relationship between SMON development and clioquinol use was never found, suggesting the interaction of another compound. Researchers have also suggested the SMON epidemic could have been due to a viral infection with an Inoue-Melnick virus.[10]

Topical use

Clioquinol is a constituent of the prescription medicine Vioform, which is a topical antifungal treatment. It is also used in the form of a cream (and in combination with betamethasone) in the treatment of inflammatory skin disorders.

Use in neurodegenerative diseases

Research at UCSF indicates that clioquinol appears to block the genetic action of Huntington's disease in mice and in cell culture.[11]

Evidence from phase 2 clinical trials suggested that clioquinol could halt cognitive decline in Alzheimer's disease, possibly owing to its ability to act as a chelator for copper and zinc ions. This led to development of analogs including PBT2 as potential therapeutic compounds for the treatment of Alzheimer's disease.[12]

Recent animal studies have shown that clioquinol can reverse the progression of Alzheimer's, Parkinson's and Huntington's diseases. According to Dr. Siegfried Hekimi and colleagues at McGill's Department of Biology, clioquinol acts directly on a protein called Clk-1, often informally called “clock-1,” and might slow down the aging process. They theorize that this may explain the apparent ability of the drug to be effective in the above conditions, but warn against individuals experimenting with this drug.[13]

Use for autism

Research at the Academica Sinica in Taiwan shows that Clioquinol may be effective in increasing the transmission of zinc to the brain, thereby correcting the zinc deficiency found in many children with autism. When this was done to mice displaying autistic behaviour, their autistic traits subsided and their behaviour became almost identical to that of mice who were not autistic. The Academica Sinica researchers hope that psychiatrists will consider prescribing the drug, which is already permitted in Taiwan, to suitable patients.[14]

Continued use and manufacture around the world

Country Comments
United States In August 2004, Prana Biotechnology, an Australian company and P.N Gerolymatos S.A (PNG) agreed to recognize each other's rights to market clioquinol in their respective territories, with PNG holding right for European territories, and Prana holding rights for US and Japan. Prana has performed research into the use of hydroxyquinolines drugs in the treatment of Alzheimers disease.
Canada In 2001, the Canadian company Paladin Labs bought the rights to market Vioform from Novartis. Vioform is licensed for use in Canada as a topical anti-fungal.
Netherlands 2004 and 2005 reports describe use in treatment of Dientamoeba fragilis and Entamoeba histolytica infection.[5][5]
India Manufactured by Vishal Laboratories and LASA Laboratory[15]

See also

  • PBT2, a related 8-hydroxyquinoline


  1. ^ "Clioquinol topical medical facts from". Retrieved 15 May 2015. 
  2. ^ Rohde W, Mikelens P, Jackson J, Blackman J, Whitcher J, Levinson W (1976). "Hydroxyquinolines inhibit ribonucleic acid-dependent deoxyribonucleic acid polymerase and inactivate Rous sarcoma virus and herpes simplex virus". Antimicrob. Agents Chemother. 10 (2): 234–40.  
  3. ^ GHOLZ LM, ARONS WL (1964). "Prophylaxis And Therapy Of Amebiasis And Shigellosis With Iodochlorhydroxyquin". Am. J. Trop. Med. Hyg. 13: 396–401.  
  4. ^ Kager PA (2005). "[Outbreak of amoebiasis in a Dutch family; tropics unexpectedly nearby]". Nederlands tijdschrift voor geneeskunde (in Dutch and Flemish) 149 (1): 51–2; author reply 52–3.  
  5. ^ a b c Bosman DK, Benninga MA, van de Berg P, Kooijman GC, van Gool T (2004). "[Dientamoeba fragilis: possibly an important cause of persistent abdominal pain in children]". Nederlands tijdschrift voor geneeskunde (in Dutch and Flemish) 148 (12): 575–9.  
  6. ^ Masters DK, Hopkins AD (1979). "Therapeutic trial of four amoebicide regimes in rural Zaire". The Journal of tropical medicine and hygiene 82 (5): 99–101.  
  7. ^ Wadia NH (1984). "SMON as seen from Bombay". Acta Neurol. Scand., Suppl. 100: 159–64.  
  8. ^ Meade TW (1975). "Subacute myelo-optic neuropathy and clioquinol. An epidemiological case-history for diagnosis". British journal of preventive & social medicine 29 (3): 157–69.  
  9. ^ Takasu T (2003). "[SMON--a model of the iatrogenic disease]". Rinsho Shinkeigaku (in Japanese) 43 (11): 866–9.  
  10. ^ Ito M, Nishibe Y, Inoue YK (1998). "Isolation of Inoue-Melnick virus from cerebrospinal fluid of patients with epidemic neuropathy in Cuba". Arch. Pathol. Lab. Med. 122 (6): 520–2.  
  11. ^ Nguyen T, Hamby A, Massa SM (2005). "Clioquinol down-regulates mutant huntingtin expression in vitro and mitigates pathology in a Huntington's disease mouse model". Proc. Natl. Acad. Sci. U.S.A. 102 (33): 11840–5.  
  12. ^ Rapid restoration of cognition in Alzheimer's transgenic mice with 8-hydroxy quinoline analogs is associated with decreased interstitial Abeta.
  13. ^ [3]
  14. ^ [4]
  15. ^ Herlekar, Omkar. "Clioquinol manufacturers India". Lasa labs. Retrieved 12 March 2013. 
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