Systematic (IUPAC) name
Clinical data
Trade names Aralen
AHFS/ monograph
Licence data US FDA:link
Pharmacokinetic data
Metabolism Liver
Half-life 1–2 months
54-05-7 7pxY
PubChem CID 2719
DrugBank DB00608 7pxY
ChemSpider 2618 7pxY
UNII 886U3H6UFF 7pxY
KEGG D02366 7pxY
ChEBI CHEBI:3638 7pxY
NIAID ChemDB 000733
Chemical data
Formula C18H26ClN3
319.872 g/mol
 14pxY (what is this?)  (verify)

Chloroquine /ˈklɔrəkwɪn/ is a 4-aminoquinoline drug used in the treatment or prevention of malaria.

Medical uses

  • Chloroquine has long been used in the treatment or prevention of malaria. After the malaria parasite Plasmodium falciparum started to develop widespread resistance to it,[1][2] new potential uses of this cheap and widely available drug have been investigated. Chloroquine has been extensively used in mass drug administrations, which may have contributed to the emergence and spread of resistance.
  • In treatment of amoebic liver abscess, chloroquine phosphate may be substituted or added in the event of failure of resolution of clinical symptoms with metronidazole or another nitroimidazole within 5 days or intolerance to metronidazole or a nitroimidazole.[3]

Malaria prevention

Chloroquine can be used for preventing malaria from Plasmodium vivax, P. ovale, and P. malariae. Popular drugs based on chloroquine phosphate (also called nivaquine) are Chloroquine FNA, Resochin, and Dawaquin. Many areas of the world have widespread strains of chloroquine-resistant P. falciparum, so other antimalarials, such as mefloquine or atovaquone, may be advisable instead. Combining chloroquine with proguanil may be more effective against chloroquine-resistant P. falciparum than treatment with chloroquine alone, but is no longer recommended by the Centers for Disease Control and Prevention due to the availability of more effective combinations.[7] For children 14 years of age or below, the dose of chloroquine is 600 mg per week.[citation needed]

Disease-modifying antirheumatic drugs

Against rheumatoid arthritis, it operates by inhibiting lymphocyte proliferation, phospholipase A2, antigen presentation in dendritic cells, release of enzymes from lysosomes, release of reactive oxygen species from macrophages, and production of IL-1.

Adverse effects

At the doses used for prevention of malaria, side effects include gastrointestinal problems, stomachache, itch, headache, postural hypotension, nightmares, and blurred vision.

Chloroquine-induced itching is very common among black Africans (70%), but much less common in other races. It increases with age, and is so severe as to stop compliance with drug therapy. It is increased during malaria fever; its severity is correlated to the malaria parasite load in blood. Some evidence indicates it has a genetic basis and is related to chloroquine action with opiate receptors centrally or peripherally.[8]

When doses are extended over a number of months, a slow onset of mood changes (i.e., depression, anxiety) can occur. These may be more pronounced with higher doses used for treatment. Chloroquine tablets have an unpleasant metallic taste. This could be avoided by ‘taste-masked and controlled release’ formulations such as multiple emulsions.[9]

Another serious side effect is toxicity to the eye or chloroquine retinopathy. This only occurs with long-term use over many years. Patients on long-term chloroquine therapy should be screened at baseline and then annually after five years of use.[10] The daily safe maximum doses for eye toxicity can be computed from one's height and weight using this calculator.[11]

Cardiac toxicity may occur also.[12] This manifests itself as either conduction disturbances (bundle-branch block, atrioventricular block) or cardiomyopathy – often with hypertrophy, restrictive physiology, and congestive heart failure. The changes may be irreversible. Only two cases have been reported requiring heart transplantation, suggesting this particular risk is very low. Electron microscopy of cardiac biopsies show pathognomonic cytoplasmic inclusion bodies. The pathology is due to its effect on the lysosomes.


Chloroquine is very dangerous in overdose. It is rapidly absorbed from the gut. In 1961, published studies showed three children who took overdoses died within 2.5 hours of taking the drug. While the amount of the overdose was not cited, the therapeutic index for chloroquine is known to be small.[13]

A metabolite of chloroquine – hydroxycloroquine – has a long half-life (32–56 days) in blood and a large volume of distribution (580–815 L/kg).[14] The therapeutic, toxic and lethal ranges are usually considered to be 0.03 to 15 mg/l, 3.0 to 26 mg/l and 20 to 104 mg/l, respectively. However, nontoxic cases have been reported in the range 0.3 to 39 mg/l, suggesting individual tolerance to this agent may be more variable than previously recognised.[14]

Resistance in malaria

Since the first documentation of P. falciparum chloroquine resistance in the 1950s, resistant strains have appeared throughout East and West Africa, Southeast Asia, and South America. The effectiveness of chloroquine against P. falciparum has declined as resistant strains of the parasite evolved. They effectively neutralize the drug via a mechanism that drains chloroquine away from the digestive vacuole. Chloroquine-resistant cells efflux chloroquine at 40 times the rate of chloroquine-sensitive cells; the related mutations trace back to transmembrane proteins of the digestive vacuole, including sets of critical mutations in the P. falciparum chloroquine resistance transporter (PfCRT) gene. The mutated protein, but not the wild-type transporter, transports chloroquine when expressed in Xenopus oocytes and is thought to mediate chloroquine leak from its site of action in the digestive vacuole.[15] Resistant parasites also frequently have mutated products of the ABC transporter P. falciparum multidrug resistance (PfMDR1) gene, although these mutations are thought to be of secondary importance compared to Pfcrt. Verapamil, a Ca2+ channel blocker, has been found to restore both the chloroquine concentration ability and sensitivity to this drug. Recently, an altered chloroquine-transporter protein CG2 of the parasite has been related to chloroquine resistance, but other mechanisms of resistance also appear to be involved.[16]

Other agents which have been shown to reverse chloroquine resistance in malaria are chlorpheniramine, gefitinib, imatinib, tariquidar and zosuquidar.[17]

Research on the mechanism of chloroquine and how the parasite has acquired chloroquine resistance is still ongoing, as other mechanisms of resistance are likely.


Chloroquine has a very high volume of distribution, as it diffuses into the body's adipose tissue. Chloroquine and related quinines have been associated with cases of retinal toxicity, particularly when provided at higher doses for longer times. Accumulation of the drug may result in deposits that can lead to blurred vision and blindness. With long-term doses, routine visits to an ophthalmologist are recommended.

Chloroquine is also a lysosomotropic agent, meaning it accumulates preferentially in the lysosomes of cells in the body. The pKa for the quinoline nitrogen of chloroquine is 8.5, meaning it is about 10% deprotonated at physiological pH as calculated by the Henderson-Hasselbalch equation. This decreases to about 0.2% at a lysosomal pH of 4.6. Because the deprotonated form is more membrane-permeable than the protonated form, a quantitative "trapping" of the compound in lysosomes results. (A quantitative treatment of this phenomenon involves the pKas of all nitrogens in the molecule; this treatment, however, suffices to show the principle.)

The lysosomotropic character of chloroquine is believed to account for much of its antimalarial activity; the drug concentrates in the acidic food vacuole of the parasite and interferes with essential processes. Its lysosomotropic properties further allow for its use for in vitro experiments pertaining to intracellular lipid related diseases,[18][19] autophagy, and apoptosis.[20]

Mechanism of action


File:Birefringence of malaria pigment.jpg
Hemozoin formation in P. falciparum: many antimalarials are strong inhibitors of hemozoin crystal growth.

Inside red blood cells, the malarial parasite, which is then in its asexual lifecycle stage, must degrade hemoglobin to acquire essential amino acids, which the parasite requires to construct its own protein and for energy metabolism. Digestion is carried out in a vacuole of the parasitic cell.

Hemoglobin is composed of a protein unit (digested by the parasite) and a heme unit (not used by the parasite). During this process, the parasite releases the toxic and soluble molecule heme. The heme moiety consists of a porphyrin ring called Fe(II)-protoporphyrin IX (FP). To avoid destruction by this molecule, the parasite biocrystallizes heme to form hemozoin, a nontoxic molecule. Hemozoin collects in the digestive vacuole as insoluble crystals.

Chloroquine enters the red blood cell, inhabiting the parasite cell and digestive vacuole by simple diffusion. Chloroquine then becomes protonated (to CQ2+), as the digestive vacuole is known to be acidic (pH 4.7); chloroquine then cannot leave by diffusion. Chloroquine caps hemozoin molecules to prevent further biocrystallization of heme, thus leading to heme buildup. Chloroquine binds to heme (or FP) to form the FP-chloroquine complex; this complex is highly toxic to the cell and disrupts membrane function. Action of the toxic FP-chloroquine and FP results in cell lysis and ultimately parasite cell autodigestion. In essence, the parasite cell drowns in its own metabolic products.[21] Parasites that do not form hemozoin are therefore resistant to chloroquine.[22]

In humans

Chloroquine inhibits thiamine uptake.[23] It acts specifically on the transporter SLC19A3.


Chloroquine was discovered in 1934 by Hans Andersag and coworkers at the Bayer laboratories, who named it "Resochin".[24] It was ignored for a decade because it was considered too toxic for human use. During World War II, United States government-sponsored clinical trials for antimalarial drug development showed unequivocally that chloroquine has a significant therapeutic value as an antimalarial drug. It was introduced into clinical practice in 1947 for the prophylactic treatment of malaria.[25]


According to research published in the journal PLoS ONE, an overuse of chloroquine treatment has led to the development of a specific strain of E. coli that is now resistant to the powerful antibiotic ciprofloxacin.[26]

See also


  1. Plowe CV (2005). "Antimalarial drug resistance in Africa: strategies for monitoring and deterrence". Curr. Top. Microbiol. Immunol. Current Topics in Microbiology and Immunology 295: 55–79. ISBN 3-540-25363-7. PMID 16265887. doi:10.1007/3-540-29088-5_3. 
  2. Uhlemann AC, Krishna S (2005). "Antimalarial multi-drug resistance in Asia: mechanisms and assessment". Curr. Top. Microbiol. Immunol. Current Topics in Microbiology and Immunology 295: 39–53. ISBN 3-540-25363-7. PMID 16265886. doi:10.1007/3-540-29088-5_2. 
  4. Savarino A, Boelaert JR, Cassone A, Majori G, Cauda R (November 2003). "Effects of chloroquine on viral infections: an old drug against today's diseases?". Lancet Infect Dis 3 (11): 722–7. PMID 14592603. doi:10.1016/S1473-3099(03)00806-5. 
  5. Savarino A, Lucia MB, Giordano F, Cauda R (October 2006). "Risks and benefits of chloroquine use in anticancer strategies". Lancet Oncol. 7 (10): 792–3. PMID 17012039. doi:10.1016/S1470-2045(06)70875-0. 
  6. Sotelo J, Briceño E, López-González MA (March 2006). "Adding chloroquine to conventional treatment for glioblastoma multiforme: a randomized, double-blind, placebo-controlled trial". Ann. Intern. Med. 144 (5): 337–43. PMID 16520474. doi:10.7326/0003-4819-144-5-200603070-00008. 
    "Summaries for patients. Adding chloroquine to conventional chemotherapy and radiotherapy for glioblastoma multiforme". Ann. Intern. Med. 144 (5): I31. March 2006. PMID 16520470. doi:10.7326/0003-4819-144-5-200603070-00004. 
  7. CDC. Health information for international travel 2001–2002. Atlanta, Georgia: U.S. Department of Health and Human Services, Public Health Service, 2001.
  8. Ajayi AA (September 2000). "Mechanisms of chloroquine-induced pruritus". Clin. Pharmacol. Ther. 68 (3): 336. PMID 11014416. 
  10. Michaelides M, Stover NB, Francis PJ, Weleber RG (2011). "Retinal toxicity associated with hydroxychloroquine and chloroquine: risk factors, screening, and progression despite cessation of therapy". Arch Ophthalmol 129 (1): 30–39. PMID 21220626. doi:10.1001/archophthalmol.2010.321. 
  11. " – Determine the safe dose of medicines: Chloroquine and Hydroxychloroquine (Plaquenil)". Retrieved 21 February 2008. 
  12. E. Tönnesmann, R. Kandolf, T. Lewalter: Chloroquine cardiomyopathy – a review of the literature. Immunopharmacol Immunotoxicol 2013, 35(3): 434–442
  13. Cann HM, Verhulst HL (1 January 1961). "Fatal acute chloroquine poisoning in children" (ABSTRACT). Pediatrics 27 (1): 95–102. PMID 13690445. 
  14. 14.0 14.1 Molina DK (2011) Postmortem hydroxychloroquine concentrations in nontoxic cases. Am J Forensic Med Pathol
  15. Martin RE, Marchetti RV, Cowan AI et al.(September 2009). "Chloroquine transport via the malaria parasite's chloroquine resistance transporter". Science 325(5948): 1680–1682:
  16. Essentials of medical pharmacology fifth edition 2003,reprint 2004, published by-Jaypee Brothers Medical Publisher Ltd, 2003,KD tripathi, page 739,740.
  17. Alcantara LM, Kim J, Moraes CB, Franco CH, Franzoi KD, Lee S, Freitas-Junior LH, Ayong LS (2013) Chemosensitization potential of P-glycoprotein inhibitors in malaria parasites. Exp Parasitol pii: S0014-4894(13)00092-1. doi:10.1016/j.exppara.2013.03.022x
  18. Chen, Patrick; Gombart, Z and Chen J (2011). "Chloroquine treatment of ARPE-19 cells leads to lysosome dilation and intracellular lipid accumulation: possible implications of lysosomal dysfunction in macular degeneration". Cell & Bioscience 1 (10): 10. doi:10.1186/2045-3701-1-10. 
  19. Kurup, Pradeep; Zhang Y; Xu J et al. (2010). "Aβ–mediated NMDA receptor endocytosis in Alzheimer's disease involves ubiquitination of the tyrosine phosphatase STEP61". Neurobiology of Disease 30 (17): 5948–57. PMC 2868326. PMID 20427654. doi:10.1523/JNEUROSCI.0157-10.2010. 
  20. Kim, Ella; Wustenberg R; Rusbam A et al. (2010). "Chloroquine activates the p53 pathway and induces apoptosis in human glioma cells". Neuro-oncology 12 (4): 389–400. PMC 2940600. PMID 20308316. doi:10.1093/neuonc/nop046. 
  21. Hempelmann E. (2007). "Hemozoin biocrystallization in Plasmodium falciparum and the antimalarial activity of crystallization inhibitors". Parasitol Research 100 (4): 671–676. PMID 17111179. doi:10.1007/s00436-006-0313-x. 
  22. Lin JW, Spaccapelo R, Schwarzer E et al. (2015). "Replication of Plasmodium in reticulocytes can occur without hemozoin formation, resulting in chloroquine resistance.". J Exp Med. PMID 25941254. 
  23. Huang Z, Srinivasan S, Zhang J, Chen K, Li Y, Li W, Quiocho FA, Pan X (2012) Discovering thiamine transporters as targets of chloroquine using a novel functional genomics strategy" PLoS Genet 8(11) e1003083. doi:10.1371/journal.pgen.1003083 open access publication - free to read
  24. Krafts K, Hempelmann E, Skórska-Stania A (2012). "From methylene blue to chloroquine: a brief review of the development of an antimalarial therapy". Parasitol Res 11 (1): 1–6. PMID 22411634. doi:10.1007/s00436-012-2886-x. 
  25. "The History of Malaria, an Ancient Disease". Centers for Disease Control. 
  26. Davidson RJ, Davis I, Willey BM (2008). Frenck, Robert, ed. "Antimalarial Therapy Selection for Quinolone Resistance among Escherichia coli in the Absence of Quinolone Exposure, in Tropical South America". PLoS ONE 3 (7): e2727. Bibcode:2008PLoSO...3.2727D. PMC 2481278. PMID 18648533. doi:10.1371/journal.pone.0002727.  open access publication - free to read

External links

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