Chloroquine

Malaria Chloroquine has been used in the treatment and prevention of malaria from Plasmodium vivax, P. ovale, and P. malariae. It is generally not used for Plasmodium falciparum as there is widespread resistance to it. Chloroquine has been extensively used in mass drug administrations, which may have contributed to the emergence and spread of resistance. It is recommended to check if chloroquine is still effective in the region prior to using it. In areas where resistance is present, other antimalarials, such as mefloquine or atovaquone, may be used instead. The Centers for Disease Control and Prevention recommend against treatment of malaria with chloroquine alone due to more effective combinations. Amebiasis In treatment of amoebic liver abscess, chloroquine may be used instead of or in addition to other medications in the event of failure of improvement with metronidazole or another nitroimidazole within five days or intolerance to metronidazole or a nitroimidazole. Rheumatic disease As it mildly suppresses the immune system, chloroquine is used in some autoimmune disorders, such as rheumatoid arthritis and has an off-label indication for lupus erythematosus. == Side effects ==

Side effects include blurred vision, nausea, vomiting, abdominal cramps, headache, diarrhea, swelling legs/ankles, shortness of breath, pale lips/nails/skin, muscle weakness, easy bruising/bleeding, hearing and mental problems. • Unwanted/uncontrolled movements (including tongue and face twitching, diskenesia, and dystonia) • 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. • Triggering of a severe psoriasis attack in those with psoriasis • Chloroquine retinopathy (irreversible retinal damage) • 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. • Pancytopenia, aplastic anemia, reversible agranulocytosis, low blood platelets, neutropenia • Worsening of the condition for those with porphyria Small amounts of chloroquine are excreted in the breast milk of lactating women. However, this drug can be safely prescribed to infants, the effects are not harmful. Studies with mice show that radioactively tagged chloroquine passed through the placenta rapidly and accumulated in the fetal eyes which remained present five months after the drug was cleared from the rest of the body. Women who are pregnant or planning on getting pregnant are still advised against traveling to malaria-risk regions. Elderly There is not enough evidence to determine whether chloroquine is safe to be given to people aged 65 and older. Since it is cleared by the kidneys, toxicity should be monitored carefully in people with poor kidney functions, as is more likely to be the case in the elderly. == Drug interactions ==

Chloroquine has a number of drug–drug interactions that might be of clinical concern: • Ampicillin levels may be reduced by chloroquine; • Antacids may reduce absorption of chloroquine; • Cimetidine may inhibit metabolism of chloroquine; increasing levels of chloroquine in the body; • Cyclosporine levels may be increased by chloroquine; and • Mefloquine may increase risk of convulsions. == Overdose ==

Chloroquine, in overdose, has a risk of death of about 20%. It is rapidly absorbed from the gut with an onset of symptoms generally within an hour. Treatment recommendations include early mechanical ventilation, cardiac monitoring, and activated charcoal. Intravenous fluids and vasopressors may be required with epinephrine being the vasopressor of choice. Seizures may be treated with benzodiazepines. Intravenous potassium chloride may be required, however this may result in high blood potassium later in the course of the disease. Dialysis has not been found to be useful. == Pharmacology ==

Absorption of chloroquine is rapid and primarily happens in the gastrointestinal tract. It is widely distributed in body tissues. Protein binding in plasma ranges from 46% to 79%. Its metabolism is partially hepatic, giving rise to its main metabolite, desethylchloroquine. Its excretion is ≥50% as unchanged drug in urine, where acidification of urine increases its elimination. It has a very high volume of distribution, as it diffuses into the body's adipose tissue. Accumulation of the drug may result in deposits that can lead to blurred vision and blindness. It and related quinines have been associated with cases of retinal toxicity, particularly when provided at higher doses for longer times. 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 (per 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. == Mechanism of action ==

Malaria formation in P. falciparum: many antimalarials are strong inhibitors of hemozoin crystal growth. 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, autophagy, and apoptosis. 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 by simple diffusion, inhibiting the parasite cell and digestive vacuole. Chloroquine (CQ) 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. Parasites that do not form hemozoin are therefore resistant to chloroquine. 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. Resistant parasites are able to rapidly remove chloroquine from the digestive vacuole using a transmembrane pump. Chloroquine-resistant parasites pump chloroquine out at 40 times the rate of chloroquine-sensitive parasites; the pump is coded by the P. falciparum chloroquine resistance transporter (PfCRT) gene. The natural function of the chloroquine pump is to transport peptides: mutations to the pump that allow it to pump chloroquine out impairs its function as a peptide pump and comes at a cost to the parasite, making it less fit. Resistant parasites also frequently have mutation in the ABC transporter P. falciparum multidrug resistance (PfMDR1) gene, although these mutations are thought to be of secondary importance compared to PfCRT. An altered chloroquine-transporter protein, CG2 has been associated with chloroquine resistance, but other mechanisms of resistance also appear to be involved. Verapamil, a Ca2+ channel blocker, has been found to restore both the chloroquine concentration ability and sensitivity to this drug. Other agents which have been shown to reverse chloroquine resistance in malaria are chlorpheniramine, gefitinib, imatinib, tariquidar and zosuquidar. chloroquine is still effective against poultry malaria in Thailand. Sohsuebngarm et al. 2014 tested P. gallinaceum at Chulalongkorn University and found that the parasite is not resistant. Sertraline, fluoxetine and paroxetine reverse chloroquine resistance, making resistant biotypes susceptible if used in a cotreatment. Antiviral Chloroquine has antiviral effects against some viruses. It increases late endosomal and lysosomal pH, resulting in impaired release of the virus from the endosome or lysosome — release of the virus requires a low pH. The virus is therefore unable to release its genetic material into the cell and replicate. Chloroquine also seems to act as a zinc ionophore that allows extracellular zinc to enter the cell and inhibit viral RNA-dependent RNA polymerase. Other Chloroquine inhibits thiamine uptake. It acts specifically on the transporter SLC19A3. 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. == History ==

In Peru, the indigenous people extracted the bark of the Cinchona tree (Cinchona officinalis) and used the extract to fight chills and fever in the seventeenth century. In 1633, this herbal medicine was introduced in Europe, where it was given the same use and also began to be used against malaria. The quinoline antimalarial drug quinine was isolated from the extract in 1820. After World War I, the German government sought alternatives to quinine. Chloroquine, a synthetic analogue with the same mechanism of action was discovered in 1934, by Hans Andersag and coworkers at the Bayer laboratories, who named it resochin. It was ignored for a decade, because it was considered too toxic for human use. Instead, in World War II, the German Africa Corps used the chloroquine analogue 3-methyl-chloroquine, known as sontochin. After Allied forces arrived in Tunis, sontochin fell into the hands of Americans, who sent the material back to the United States for analysis, leading to renewed interest in chloroquine. United States government-sponsored clinical trials for antimalarial drug development showed unequivocally that chloroquine has a significant therapeutic value as an antimalarial drug. Chemical synthesis The first synthesis of chloroquine was disclosed in a patent filed by IG Farben in 1937. In the final step, 4,7-dichloroquinoline was reacted with 1-diethylamino-4-aminopentane. : By 1949, chloroquine manufacturing processes had been established to allow its widespread use. == Society and culture ==

Formulations Chloroquine comes in tablet form as the phosphate, sulfate, and hydrochloride salts. Chloroquine is usually dispensed as the phosphate. Names Brand names include Chloroquine FNA, Resochin, Dawaquin, and Lariago. == Other animals ==

Chloroquine, in various chemical forms, is used to treat and control surface growth of anemones and algae, and many protozoan infections in aquariums, e.g. the fish parasite Amyloodinium ocellatum. It is also used in poultry malaria. == Research ==

In biomedicinal science, chloroquine is used for in vitro experiments to inhibit lysosomal degradation of protein products. SARS-CoV Chloroquine was proposed as a treatment for SARS, with in vitro tests inhibiting the severe acute respiratory syndrome coronavirus (SARS-CoV). In October 2004, a published report stated that chloroquine acts as an effective inhibitor of the replication of SARS-CoV in vitro. COVID-19 Other Chloroquine was being considered in 2003, in pre-clinical models as a potential agent against chikungunya fever. The radiosensitizing and chemosensitizing properties of chloroquine are being evaluated for anticancer strategies in humans. Chloroquine and its modified forms have also been evaluated as treatment options for inflammatory conditions like rheumatoid arthritis and inflammatory bowel disease. == References ==