Hydroxychloroquine (HCQ), sold under the brand name Plaquenil among others, is a medication used for the prevention and treatment of certain types of malaria. Specifically it is used for chloroquine-sensitive malaria. Other uses include treatment of rheumatoid arthritis, lupus, and porphyria cutanea tarda. It is taken by mouth. It is also being used as an experimental treatment for coronavirus disease 2019 (COVID-19).
Common side effects include vomiting, headache, changes in vision and muscle weakness. Severe side effects may include allergic reactions. Although all risk cannot be excluded it remains a treatment for rheumatic disease during pregnancy. Hydroxychloroquine is in the antimalarial and 4-aminoquinoline families of medication.
Hydroxychloroquine was approved for medical use in the United States in 1955. It is on the World Health Organization’s List of Essential Medicines, the safest and most effective medicines needed in a health system. The wholesale cost in the developing world is about US$4.65 per month as of 2015, when used for rheumatoid arthritis or lupus. In the United States the wholesale cost of a month of treatment is about US$25 as of 2020. In the United Kingdom this dose costs the NHS about £ 5.15. In 2017, it was the 128th most prescribed medication in the United States with more than five million prescriptions.
Hydroxychloroquine treats malaria, systemic lupus erythematosus, rheumatic disorders like rheumatoid arthritis, porphyria cutanea tarda, and Q fever.
In 2014, its efficacy to treat Sjögren syndrome was questioned in a double-blind study involving 120 patients over a 48-week period.
Hydroxychloroquine is widely used in the treatment of post-Lyme arthritis. It may have both an anti-spirochaete activity and an anti-inflammatory activity, similar to the treatment of rheumatoid arthritis.
The drug label advises that hydroxychloroquine should not be prescribed to individuals with known hypersensitivity to 4-Aminoquinoline compounds. There are a range of other contraindications  and caution is required if patients have certain heart conditions, diabetes, psoriasis etc.
The most common adverse effects are a mild nausea and occasional stomach cramps with mild diarrhea. The most serious adverse effects affect the eye, with dose-related retinopathy as a concern even after hydroxychloroquine use is discontinued. For short-term treatment of acute malaria, adverse effects can include abdominal cramps, diarrhea, heart problems, reduced appetite, headache, nausea and vomiting.
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, 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.
One of the most serious side effects is retinopathy (generally with chronic use). People taking 400 mg of hydroxychloroquine or less per day generally have a negligible risk of macular toxicity, whereas the risk begins to go up when a person takes the medication over 5 years or has a cumulative dose of more than 1000 grams. The daily safe maximum dose for eye toxicity can be computed from one’s height and weight using this calculator. Cumulative doses can also be calculated from this calculator. 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.
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.
Due to rapid absorption, symptoms of overdose can occur within a half an hour after ingestion. Overdose symptoms include convulsions, drowsiness, headache, heart problems or heart failure, difficulty breathing and vision problems.
Hydroxychloroquine overdoses are rarely reported, with 7 previous cases found in the English medical literature. In one such case, a 16-year-old girl who had ingested a handful of hydroxychloroquine 200mg presented with tachycardia (heart rate 110 beats/min), hypotension (systolic blood pressure 63 mm Hg), central nervous system depression, conduction defects (ORS = 0.14 msec), and hypokalemia (K = 2.1 meq/L). Treatment consisted of fluid boluses and dopamine, oxygen, and potassium supplementation. The presence of hydroxychloroquine was confirmed through toxicologic tests. The patient’s hypotension resolved within 4.5 hours, serum potassium stabilized in 24 hours, and tachycardia gradually decreased over 3 days.
The drug transfers into breast milk and should be used with care by pregnant or nursing mothers.
Care should be taken if combined with medication altering liver function as well as aurothioglucose (Solganal), cimetidine (Tagamet) or digoxin (Lanoxin). HCQ 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 HCQ. Both neostigmine and pyridostigmine antagonize the action of hydroxychloroquine.
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.
Specifically, the FDA drug label for hydroxychloroquine lists the following drug interactions :
- Digoxin (wherein it may result in increased serum digoxin levels)
- Insulin or antidiabetic drugs (wherein it may enhance the effects of a hypoglycemic treatment)
- Drugs that prolong QT interval and other arrhythmogenic drugs (as Hydroxychloroquine prolongs the QT interval and may increase the risk of inducing ventricular arrhythmias if used concurrently)
- Mefloquine and other drugs known to lower the convulsive 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 cylcosporin level was reported when used together).
Hydroxychloroquine has similar pharmacokinetics to chloroquine, with rapid gastrointestinal absorption and elimination by the kidneys. Cytochrome P450 enzymes (CYP2D6, 2C8, 3A4 and 3A5) metabolize hydroxychloroquine to N-desethylhydroxychloroquine.
Antimalarials are lipophilic weak bases and easily pass plasma membranes. The free base form accumulates in lysosomes (acidic cytoplasmic vesicles) and is then protonated, resulting in concentrations within lysosomes up to 1000 times higher than in culture media. This increases the pH of the lysosome from 4 to 6. Alteration in pH causes inhibition of lysosomal acidic proteases causing a diminished proteolysis effect. Higher pH within lysosomes causes decreased intracellular processing, glycosylation and secretion of proteins with many immunologic and nonimmunologic consequences. These effects are believed to be the cause of a decreased immune cell functioning such as chemotaxis, phagocytosis and superoxide production by neutrophils. HCQ 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.
Mechanism of action
Hydroxychloroquine increases lysosomal pH in antigen-presenting cells. In inflammatory conditions, it blocks toll-like receptors on plasmacytoid dendritic cells (PDCs). Hydroxychloroquine, by decreasing TLR signaling, reduces the activation of dendritic cells and the inflammatory process. Toll-like receptor 9 (TLR 9) recognizes DNA-containing immune complexes and leads to the production of interferon and causes the dendritic cells to mature and present antigen to T cells, therefore reducing anti-DNA auto-inflammatory process.
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.
As with other quinoline antimalarial drugs, the 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 their deaths.
It is frequently sold as a sulfate salt known as hydroxychloroquine sulfate. 200 mg of the sulfate salt is equal to 155 mg of the base.
Brand names of hydroxychloroquine include Plaquenil, Hydroquin, Axemal (in India), Dolquine, Quensyl, Quinoric.
Hydroxychloroquine and chloroquine have been recommended by Chinese and South Korean health authorities for the experimental treatment of COVID-19. In vitro studies in cell cultures demonstrated that hydroxychloroquine was more potent than chloroquine against SARS-CoV-2.
On 17 March 2020, the AIFA Scientific Technical Commission of the Italian Medicines Agency expressed a favorable opinion on including the off-label use of chloroquine and hydroxychloroquine for the treatment of SARS-CoV-2 infection.
white solid (0.263 g, 78%). 1H NMR
(600 MHz, CDCl3
) δ 8.48 (d, J = 5.4 Hz, 1H), 7.93 (d, J = 5.4 Hz, 1H), 7.70 (d, J = 9.2 Hz, 1H), 7.34 (dd, J = 8.8, 7.3 Hz, 1H), 6.39 (d, J = 5.4 Hz, 1H), 4.96 (d, J = 7.5 Hz, 1H), 3.70 (sx,J = 6.8 Hz, 1H), 3.55 (m, 2H), 2.57 (m, 5H), 2.49 (m, 2H),
1.74–1.62 (m, 1H), 1.65–1.53 (m, 3H), 1.31 (d, J = 6.9 Hz, 3H),
1.24 (d, J = 7.2 Hz, 2H);
13C NMR (125 MHz, CDCl3) δ 152.2,
149.5, 149.2, 135.0, 129.0, 125.4, 121.2, 117.4, 99.4, 58.6, 54.9,
53.18, 48.5, 47.9, 34.5, 24.1, 20.6, 11.9. Spectra were obtained
in accordance with those previously reported [38,39].
38. Cornish, C. A.; Warren, S. J. Chem. Soc., Perkin Trans. 1 1985,
39. Münstedt, R.; Wannagat, U.; Wrobel, D. J. Organomet. Chem. 1984,
264, 135–148. doi:10.1016/0022-328X(84)85139-6
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Hydroxychloroquine freebase molecule
|Trade names||Plaquenil, others|
|Other names||Hydroxychloroquine sulfate|
|By mouth (tablets)|
|Bioavailability||Variable (74% on average); Tmax = 2–4.5 hours|
|Elimination half-life||32–50 days|
|Excretion||Mostly Kidney (23–25% as unchanged drug), also biliary (<10%)|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||335.872 g/mol g·mol−1|
|3D model (JSmol)|
///////////Hydroxychloroquine, Hydroxy chloroquine, HCQ, ヒドロキシクロロキン , covid 19, coronavirus, antimalarial, гидроксихлорохин , هيدروكسيكلوروكين , 羟氯喹 , Oxychlorochin, Plaquenil , Plaquenil®,
Thanks for this article – what is your assessment of the effect of HCQ on covid infected patients ?