hydroxychloroquine

Hydroxychloroquine treats rheumatic disorders such as systemic lupus erythematosus, rheumatoid arthritis, and porphyria cutanea tarda, and certain infections such as Q fever and certain types of malaria. It is considered the first-line treatment for systemic lupus erythematosus.{{cite journal | vauthors = Chew CY, Mar A, Nikpour M, Saracino AM | title = Hydroxychloroquine in dermatology: New perspectives on an old drug | journal = The Australasian Journal of Dermatology | volume = 61 | issue = 2 | pages = e150–e157 | date = May 2020 | pmid = 31612996 | doi = 10.1111/ajd.13168 | hdl = 11343/286501 | s2cid = 204703558 | hdl-access = free }} Certain types of malaria, resistant strains, and complicated cases require different or additional medication.

It is widely used to treat primary Sjögren syndrome but does not appear to be effective.{{cite journal | vauthors = Wang SQ, Zhang LW, Wei P, Hua H | title = Is hydroxychloroquine effective in treating primary Sjogren's syndrome: a systematic review and meta-analysis | journal = BMC Musculoskeletal Disorders | volume = 18 | issue = 1 | pages = 186 | date = May 2017 | pmid = 28499370 | pmc = 5427554 | doi = 10.1186/s12891-017-1543-z | doi-access = free }} Hydroxychloroquine is widely used in the treatment of post-Lyme arthritis. It may have both an anti-spirochete activity and an anti-inflammatory activity, similar to the treatment of rheumatoid arthritis.{{cite journal | vauthors = Steere AC, Angelis SM | title = Therapy for Lyme arthritis: strategies for the treatment of antibiotic-refractory arthritis | journal = Arthritis and Rheumatism | volume = 54 | issue = 10 | pages = 3079–86 | date = October 2006 | pmid = 17009226 | doi = 10.1002/art.22131 | doi-access = }}

The US FDA drug label advises that hydroxychloroquine should not be prescribed to individuals with known hypersensitivity to 4-aminoquinoline compounds.{{cite web|title=Plaquenil- hydroxychloroquine sulfate tablet|website=DailyMed|date=3 January 2020|url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=34496b43-05a2-45fb-a769-52b12e099341|access-date=20 March 2020}} There are several other contraindications,{{cite web|url=https://www.pdr.net/drug-summary/Plaquenil-hydroxychloroquine-sulfate-1911|title=Plaquenil (hydroxychloroquine sulfate) dose, indications, adverse effects, interactions|website=pdr.net|access-date=19 March 2020}}{{cite web|url=https://www.webmd.com/drugs/2/drug-5482/hydroxychloroquine-oral/details|title=Drugs & Medications|website=webmd.com|access-date=19 March 2020}} and caution is required if the person considered for treatment has certain heart conditions, diabetes, or psoriasis.

Hydroxychloroquine has a narrow therapeutic index, meaning there is little difference between toxic and therapeutic doses.{{cite journal | vauthors = Schmith VD, Zhou JJ, Lohmer LR | title = The Approved Dose of Ivermectin Alone is not the Ideal Dose for the Treatment of COVID-19 | journal = Clinical Pharmacology and Therapeutics | volume = 108 | issue = 4 | pages = 762–765 | date = October 2020 | pmid = 32378737 | pmc = 7267287 | doi = 10.1002/cpt.1889 }} The most common adverse effects are nausea, stomach cramps, and diarrhea. Other common adverse effects include itching and headache.{{cite journal | vauthors = Juurlink DN | title = Safety considerations with chloroquine, hydroxychloroquine and azithromycin in the management of SARS-CoV-2 infection | journal = CMAJ | volume = 192 | issue = 17 | pages = E450–E453 | date = April 2020 | pmid = 32269021 | pmc = 7207200 | doi = 10.1503/cmaj.200528 }} The most serious adverse effects affect the eye, with dose-related retinopathy as a concern even after hydroxychloroquine use is discontinued. Serious reported neuropsychiatric adverse effects of hydroxychloroquine use include agitation, mania, difficulty sleeping, hallucinations, psychosis, catatonia, paranoia, depression, and suicidal thoughts. In rare situations, hydroxychloroquine has been implicated in cases of serious skin reactions such as Stevens–Johnson syndrome, toxic epidermal necrolysis, and Drug reaction with eosinophilia and systemic symptoms. Reported blood abnormalities with its use include lymphopenia, eosinophilia, and atypical lymphocytosis.

For short-term treatment of acute malaria, adverse effects can include abdominal cramps, diarrhea, heart problems, reduced appetite, headache, nausea and vomiting. Other adverse effects noted with short-term use of Hydroxychloroquine include low blood sugar and QT interval prolongation. Idiosyncratic hypersensitivity reactions have occurred.

For prolonged treatment of lupus or rheumatoid arthritis, adverse effects include the acute symptoms, plus altered eye pigmentation, acne, anemia, bleaching of hair, blisters in mouth and eyes, blood disorders, cardiomyopathy, convulsions, vision difficulties, diminished reflexes, emotional changes, excessive coloring of the skin, hearing loss, hives, itching, liver problems or liver failure, loss of hair, muscle paralysis, weakness or atrophy, nightmares, psoriasis, reading difficulties, tinnitus, skin inflammation and scaling, skin rash, vertigo, weight loss, and occasionally urinary incontinence. Hydroxychloroquine can worsen existing cases of both psoriasis and porphyria.

Children may be especially vulnerable to developing adverse effects from hydroxychloroquine overdoses.

{{Main|Chloroquine retinopathy}}

One of the most serious side effects is retinopathy (generally with chronic use).{{cite journal | vauthors = Flach AJ | title = Improving the risk-benefit relationship and informed consent for patients treated with hydroxychloroquine | journal = Transactions of the American Ophthalmological Society | volume = 105 | pages = 191–4; discussion 195–7 | date = December 2007 | pmid = 18427609 | pmc = 2258132 }} People taking 400 mg of hydroxychloroquine or less per day generally have a negligible risk of macular toxicity, whereas the risk begins to increase when a person takes the medication over five years or has a cumulative dose of more than 1000 grams. The daily safe maximum dose for eye toxicity can be estimated from a person's height and weight.{{cite web |title=Plaquenil Risk Calculators |url= https://www.eyedock.com/plaquenil-calcs |website= EyeDock |access-date=7 April 2020 |archive-date= 8 April 2020 |archive-url= https://web.archive.org/web/20200408150454/https://www.eyedock.com/plaquenil-calcs |url-status= dead }} Macular toxicity is related to the total cumulative dose rather than the daily dose. Regular eye screening, even in the absence of visual symptoms, is recommended to begin when either of these risk factors occurs.{{cite journal | vauthors = Marmor MF, Kellner U, Lai TY, Lyons JS, Mieler WF | title = Revised recommendations on screening for chloroquine and hydroxychloroquine retinopathy | journal = Ophthalmology | volume = 118 | issue = 2 | pages = 415–22 | date = February 2011 | pmid = 21292109 | doi = 10.1016/j.ophtha.2010.11.017 | collaboration = American Academy of Ophthalmology }}

Toxicity from hydroxychloroquine may be seen in two distinct areas of the eye: the cornea and the macula. The cornea may become affected (relatively commonly) by an innocuous cornea verticillata or vortex keratopathy and is characterized by whorl-like corneal epithelial deposits. These changes bear no relationship to dosage and are usually reversible on cessation of hydroxychloroquine.

The macular changes are potentially serious. Advanced retinopathy is characterized by reduction of visual acuity and a "bull's eye" macular lesion which is absent in early involvement.

Overdoses of hydroxychloroquine are extremely rare, but extremely toxic. Eight people are known to have overdosed since the drug's introduction in the mid-1950s, of which three have died.{{cite journal | vauthors = Marquardt K, Albertson TE | title = Treatment of hydroxychloroquine overdose | journal = The American Journal of Emergency Medicine | volume = 19 | issue = 5 | pages = 420–4 | date = September 2001 | pmid = 11555803 | doi = 10.1053/ajem.2001.25774 }} Chloroquine has a risk of death in overdose in adults of about 20%, while hydroxychloroquine is estimated to be two or threefold less toxic.

Serious signs and symptoms of overdose generally occur within an hour of ingestion.{{cite journal | vauthors = Ling Ngan Wong A, Tsz Fung Cheung I, Graham CA | title = Hydroxychloroquine overdose: case report and recommendations for management | journal = European Journal of Emergency Medicine | volume = 15 | issue = 1 | pages = 16–8 | date = February 2008 | pmid = 18180661 | doi = 10.1097/MEJ.0b013e3280adcb56 | s2cid = 41205035 }} These may include sleepiness, vision changes, seizures, coma, stopping of breathing, and heart problems such as ventricular fibrillation and low blood pressure.{{cite journal | vauthors = Smith ER, Klein-Schwartz W | title = Are 1-2 dangerous? Chloroquine and hydroxychloroquine exposure in toddlers | journal = The Journal of Emergency Medicine | volume = 28 | issue = 4 | pages = 437–43 | date = May 2005 | pmid = 15837026 | doi = 10.1016/j.jemermed.2004.12.011 }} Loss of vision may be permanent.{{EMedicine|article|1229016|Chloroquine and Hydroxychloroquine Toxicity}} Low blood potassium, to levels of 1 to 2 mmol/L, may also occur.{{cite book|vauthors=Pillay VV|title=Modern Medical Toxicology|date=2012|publisher=Jaypee Brothers Publishers|isbn=978-93-5025-965-8|page=458|url=http://www.prip.edu.in/img/ebooks/VV-Pillay-Modern-Medical-Toxicology-4th-Edition.pdf#page=474|access-date=15 April 2020|archive-date=15 April 2020|archive-url=https://web.archive.org/web/20200415144916/http://www.prip.edu.in/img/ebooks/VV-Pillay-Modern-Medical-Toxicology-4th-Edition.pdf#page=474|url-status=dead}} Cardiovascular abnormalities such as QRS complex widening and QT interval prolongation may also occur.

Treatment recommendations include early mechanical ventilation, heart monitoring, and activated charcoal. Supportive treatment with intravenous fluids and vasopressors may be required with epinephrine being the vasopressor of choice. Stomach pumping may also be used.{{cite book | vauthors = Aronson JK |title=Meyler's Side Effects of Drugs: The International Encyclopedia of Adverse Drug Reactions and Interactions |date=2015 |publisher=Elsevier |isbn=978-0-444-53716-4 |page=261 |url=

https://books.google.com/books?id=NOKoBAAAQBAJ&dq=Hydroxychloroquine+overdose&pg=RA1-PA261 }} Sodium bicarbonate and hypertonic saline may be used in cases of severe QRS complex widening. 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 does not appear to be useful.

Hydroxychloroquine may be quantified in plasma or serum to confirm a diagnosis of poisoning in hospitalized victims or in whole blood to assist in a forensic investigation of a case of sudden or unexpected death. Plasma or serum concentrations are usually in a range of 0.1-1.6 mg/L during therapy and 6–20 mg/L in cases of clinical intoxication, while blood levels of 20–100 mg/L have been observed in deaths due to acute overdosage.R. Baselt, Disposition of Toxic Drugs and Chemicals in Man, 12th edition, Biomedical Publications, Foster City, CA, 2020, pp. 1024-1026.

The drug transfers into breast milk. There is no evidence that its use during pregnancy is harmful to the developing fetus and its use is not contraindicated in pregnancy.

The concurrent use of hydroxychloroquine and the antibiotic azithromycin appears to increase the risk for certain serious side effects with short-term use, such as an increased risk of chest pain, congestive heart failure, and mortality from cardiovascular causes.{{cite journal | vauthors = Meyerowitz EA, Vannier AG, Friesen MG, Schoenfeld S, Gelfand JA, Callahan MV, Kim AY, Reeves PM, Poznansky MC | display-authors = 6 | title = Rethinking the role of hydroxychloroquine in the treatment of COVID-19 | journal = FASEB Journal | volume = 34 | issue = 5 | pages = 6027–6037 | date = May 2020 | pmid = 32350928 | pmc = 7267640 | doi = 10.1096/fj.202000919 | doi-access = free }} Care should be taken if combined with medication altering liver function as well as aurothioglucose (Solganal), cimetidine (Tagamet) or digoxin (Lanoxin). Hydroxychloroquine can increase plasma concentrations of penicillamine which may contribute to the development of severe side effects. It enhances hypoglycemic effects of insulin and oral hypoglycemic agents. Dose altering is recommended to prevent profound hypoglycemia. Antacids may decrease the absorption of hydroxychloroquine. Both neostigmine and pyridostigmine antagonize the action of hydroxychloroquine.{{cite web|title=Russian Register of Medicines: Plaquenil (hydroxychloroquine) Film-coated Tablets for Oral Use. Prescribing Information|url=http://www.rlsnet.ru/tn_index_id_2615.htm|website=rlsnet.ru|publisher=Sanofi-Synthelabo|access-date=14 July 2016|language=ru|url-status=live|archive-url=https://web.archive.org/web/20160816113809/http://www.rlsnet.ru/tn_index_id_2615.htm|archive-date=16 August 2016}}

While there may be a link between hydroxychloroquine and hemolytic anemia in those with glucose-6-phosphate dehydrogenase deficiency, this risk may be low in those of African descent.{{cite journal | vauthors = Mohammad S, Clowse ME, Eudy AM, Criscione-Schreiber LG | title = Examination of Hydroxychloroquine Use and Hemolytic Anemia in G6PDH-Deficient Patients | journal = Arthritis Care & Research | volume = 70 | issue = 3 | pages = 481–485 | date = March 2018 | pmid = 28556555 | doi = 10.1002/acr.23296 | s2cid = 3545376 | doi-access = }}

Specifically, the US Food and Drug Administration's (FDA) drug label for hydroxychloroquine lists the following drug interactions:

• Digoxin (wherein it may result in increased serum digoxin levels)
• Insulin or anti-diabetic medication (wherein it may enhance the effects of a hypoglycemic treatment)
• Drugs that prolong the QT interval such as methadone, and other arrhythmogenic drugs, as hydroxychloroquine prolongs the QT interval and may increase the risk of inducing serious abnormal heart rhythms (ventricular arrhythmias) if used concurrently.{{cite web|url=https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-provides-urgent-guidance-approach-to-identify-patients-at-risk-of-drug-induced-sudden-cardiac-death-from-use-of-off-label-covid-19-treatments/|title=Guidance on patients at risk of drug-induced sudden cardiac death from off-label COVID-19 treatments|website=newsnetwork.mayoclinic.org |date=25 March 2020}}
• Mefloquine and other drugs known to lower the seizure threshold (co-administration with other antimalarials known to lower the convulsion threshold may increase risk of convulsions)
• Antiepileptics (concurrent use may impair the antiepileptic activity)
• Methotrexate (combined use is unstudied and may increase the frequency of side effects)
• Cyclosporin (wherein an increased plasma cyclosporin level was reported when used together).

Hydroxychloroquine has similar pharmacokinetics to chloroquine, with rapid gastrointestinal absorption, large distribution volume,{{cite journal | vauthors = Schrezenmeier E, Dörner T | title = Mechanisms of action of hydroxychloroquine and chloroquine: implications for rheumatology | journal = Nature Reviews. Rheumatology | volume = 16 | issue = 3 | pages = 155–166 | date = March 2020 | pmid = 32034323 | doi = 10.1038/s41584-020-0372-x | doi-access = free }} and elimination by the kidneys; T_max is 2–4.5 hours. Cytochrome P450 enzymes (CYP2D6, 2C8, 3A4 and 3A5) metabolize hydroxychloroquine to N-desethylhydroxychloroquine.{{cite journal | vauthors = Kalia S, Dutz JP | title = New concepts in antimalarial use and mode of action in dermatology | journal = Dermatologic Therapy | volume = 20 | issue = 4 | pages = 160–74 | date = July 2007 | pmid = 17970883 | pmc = 7163426 | doi = 10.1111/j.1529-8019.2007.00131.x }} Both agents also inhibit CYP2D6 activity and may interact with other medications that depend on this enzyme.

Antimalarials are lipophilic weak bases and easily pass plasma membranes. The free base form accumulates in lysosomes (acidic cytoplasmic vesicles) and is then protonated,{{cite journal | vauthors = Kaufmann AM, Krise JP | title = Lysosomal sequestration of amine-containing drugs: analysis and therapeutic implications | journal = Journal of Pharmaceutical Sciences | volume = 96 | issue = 4 | pages = 729–46 | date = April 2007 | pmid = 17117426 | doi = 10.1002/jps.20792 }} resulting in concentrations within lysosomes up to 1,000 times higher than in culture media. This increases the pH of the lysosome from four to six.{{cite journal | vauthors = Ohkuma S, Poole B | title = Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 75 | issue = 7 | pages = 3327–31 | date = July 1978 | pmid = 28524 | pmc = 392768 | doi = 10.1073/pnas.75.7.3327 | bibcode = 1978PNAS...75.3327O | doi-access = free }} Alteration in pH causes inhibition of lysosomal acidic proteases causing a diminished proteolysis effect.{{cite journal | vauthors = Ohkuma S, Chudzik J, Poole B | title = The effects of basic substances and acidic ionophores on the digestion of exogenous and endogenous proteins in mouse peritoneal macrophages | journal = The Journal of Cell Biology | volume = 102 | issue = 3 | pages = 959–66 | date = March 1986 | pmid = 3949884 | pmc = 2114118 | doi = 10.1083/jcb.102.3.959 }} Higher pH within lysosomes causes decreased intracellular processing, glycosylation and secretion of proteins with many immunologic and nonimmunologic consequences.{{cite journal | vauthors = Oda K, Koriyama Y, Yamada E, Ikehara Y | title = Effects of weakly basic amines on proteolytic processing and terminal glycosylation of secretory proteins in cultured rat hepatocytes | journal = The Biochemical Journal | volume = 240 | issue = 3 | pages = 739–45 | date = December 1986 | pmid = 3493770 | pmc = 1147481 | doi = 10.1042/bj2400739 }} These effects are believed to be the cause of a decreased immune cell functioning such as chemotaxis, phagocytosis and superoxide production by neutrophils.{{cite journal | vauthors = Hurst NP, French JK, Gorjatschko L, Betts WH | title = Chloroquine and hydroxychloroquine inhibit multiple sites in metabolic pathways leading to neutrophil superoxide release | journal = The Journal of Rheumatology | volume = 15 | issue = 1 | pages = 23–7 | date = January 1988 | pmid = 2832600 | id = {{INIST|7127371}} }} Hydroxychloroquine is a weak diprotic base that can pass through the lipid cell membrane and preferentially concentrate in acidic cytoplasmic vesicles. The higher pH of these vesicles in macrophages or other antigen-presenting cells limits the association of autoantigenic (any) peptides with class II MHC molecules in the compartment for peptide loading and/or the subsequent processing and transport of the peptide-MHC complex to the cell membrane.{{cite journal | vauthors = Fox R | title = Anti-malarial drugs: possible mechanisms of action in autoimmune disease and prospects for drug development | journal = Lupus | volume = 5 | issue = 1 Suppl | pages = S4-10 | date = June 1996 | pmid = 8803903 | doi = 10.1177/0961203396005001031 | s2cid = 208217074 }}

Hydroxychloroquine increases{{cite book | vauthors = Waller D, Sampson T |edition=2nd|title=Medical Pharmacology and Therapeutics|page=370}} lysosomal pH in antigen-presenting cells by two mechanisms: As a weak base, it is a proton acceptor and via this chemical interaction, its accumulation in lysozymes raises the intralysosomal pH, but this mechanism does not fully account for the effect of hydroxychloroquine on pH. Additionally, in parasites that are susceptible to hydroxychloroquine, it interferes with the endocytosis and proteolysis of hemoglobin and inhibits the activity of lysosomal enzymes, thereby raising the lysosomal pH by more than two orders of magnitude over the weak base effect alone.{{cite journal | vauthors = Krogstad DJ, Schlesinger PH | title = The basis of antimalarial action: non-weak base effects of chloroquine on acid vesicle pH | journal = The American Journal of Tropical Medicine and Hygiene | volume = 36 | issue = 2 | pages = 213–20 | date = March 1987 | pmid = 2435182 | doi = 10.4269/ajtmh.1987.36.213 }}{{cite journal | vauthors = Al-Bari MA | title = Targeting endosomal acidification by chloroquine analogs as a promising strategy for the treatment of emerging viral diseases | journal = Pharmacology Research & Perspectives | volume = 5 | issue = 1 | pages = e00293 | date = February 2017 | pmid = 28596841 | pmc = 5461643 | doi = 10.1002/prp2.293 }} In 2003, a novel mechanism was described wherein hydroxychloroquine inhibits stimulation of the toll-like receptor (TLR) 9 family receptors. TLRs are cellular receptors for microbial products that induce inflammatory responses through activation of the innate immune system.{{cite journal | vauthors = Takeda K, Kaisho T, Akira S | title = Toll-like receptors | journal = Annual Review of Immunology | volume = 21 | issue = 1 | pages = 335–76 | date = April 2003 | pmid = 12524386 | doi = 10.1146/annurev.immunol.21.120601.141126 }}

As with other quinoline antimalarial drugs, the antimalarial mechanism of action of quinine has not been fully resolved. The most accepted model is based on hydrochloroquinine and involves the inhibition of hemozoin biocrystallization, which facilitates the aggregation of cytotoxic heme. Free cytotoxic heme accumulates in the parasites, causing death.{{cite journal | vauthors = Sullivan DJ | title = Theories on malarial pigment formation and quinoline action | journal = International Journal for Parasitology | volume = 32 | issue = 13 | pages = 1645–53 | date = December 2002 | pmid = 12435449 | doi = 10.1016/s0020-7519(02)00193-5 }}

Hydroxychloroquine increases the risk of low blood sugar through several mechanisms. These include decreased clearance of the hormone insulin from the blood, increased insulin sensitivity, and increased release of insulin from the pancreas.

After World War I, the German government sought alternatives to quinine as an anti-malarial. Chloroquine, a synthetic analogue with the same mechanism of action was discovered in 1934, by Hans Andersag and coworkers at the Bayer laboratories.{{cite journal | vauthors = Kouznetsov VV, Amado Torres DF |title=Antimalarials: construction of molecular hybrids based on chloroquine |journal=Universitas Scientiarum |date=September 2008 |volume=13 |issue=3 |pages=306–320 |url=http://www.scielo.org.co/scielo.php?pid=S0122-74832008000300010&script=sci_arttext }}{{cite book |isbn=9780309092180 |doi=10.17226/11017|doi-access=free| veditors = Arrow KJ, Panosian CB, Gelband H |title=Saving lives, buying time : economics of malaria drugs in an age of resistance|date=2004|publisher=National Academies Press|pmid=25009879| collaboration=Institute of Medicine (US) Committee on the Economics of Antimalarial Drugs | vauthors = Arrow KJ, Panosian C, Gelband H }}{{rp|130–131}} This was introduced into clinical practice in 1947 for the prophylactic treatment of malaria.{{cite web | url = https://www.cdc.gov/malaria/history/index.htm#chloroquine | title = The History of Malaria, an Ancient Disease | publisher = Centers for Disease Control | url-status = live | archive-url = https://web.archive.org/web/20100828183012/http://www.cdc.gov//malaria//history//index.htm#chloroquine | archive-date = 28 August 2010| date = 29 July 2019 }} Researchers subsequently attempted to discover structural analogs with superior properties and one of these was hydroxychloroquine.{{cite journal |doi=10.1021/ja01160a116 |title=The Preparation of 7-Chloro-4-(4-(N-ethyl-N-β-hydroxyethylamino)-1- methylbutylamino)-quinoline and Related Compounds |year=1950 | vauthors = Surrey AR, Hammer HF |journal=Journal of the American Chemical Society |volume=72 |issue=4 |pages=1814–1815 |bibcode=1950JAChS..72.1814S }}

The first synthesis of hydroxychloroquine was disclosed in a patent filed by Sterling Drug in 1949.{{cite patent |country=US |number=2546658 |status=patent |gdate=1951-03-27 |fdate=1949-07-23 |pridate=1949-07-23 |invent1 =Surrey, Alexander R |title=7-chloro-4-[5-(N-ethyl-N-2-hydroxyethylamino)-2-pentyl] aminoquinoline, its acid addition salts, and method of preparation |assign1= Sterling Drug Inc.}} In the final step, 4,7-dichloroquinoline was reacted with a primary amine which in turn had been made from the chloro-ketone shown:

: File:Hydroxychloroquine synthesis.svg

It is frequently sold as a sulfate salt known as hydroxychloroquine sulfate. In the sulfate salt form, 200 mg is equal to 155 mg of the pure form.

Brand names of hydroxychloroquine include Plaquenil, Hydroquin, Axemal (in India), Dolquine, Quensyl, and Quinoric.{{cite web|title=Hydroxychloroquine trade names|url=https://drugs-about.com/ing/hydroxychloroquine.html|website=Drugs-About.com|access-date=18 June 2019 }}

{{Excerpt|Chloroquine and hydroxychloroquine during the COVID-19 pandemic}}

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