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What is Chloroquine? Your Top 5 Questions Answered

What You Need to Know About the Antimalarial Drug, Chloroquine

Chloroquine is an antimalarial drug used in the prevention and treatment of malaria. It is also used to treat extraintestinal amebiasis, rheumatoid arthritis, lupus erythematosus, and several other conditions. Along with hydroxychloroquine, chloroquine has been touted as a potential treatment for COVID-19, the disease caused by the 2019 novel coronavirus. For information on the use of chloroquine and hydroxychloroquine in the treatment of COVID-19, please go to question 5: Can chloroquine treat or prevent COVID-19?.

The content on this page is provided for informational purposes only. If you have any questions or concerns about your treatment, you should talk to your doctor, pharmacist, or healthcare professional. This is particularly important if you are taking multiple medications or have any existing medical conditions.

  1. What is chloroquine?
  2. What is chloroquine used for?
  3. Are chloroquine and hydroxychloroquine the same?
  4. What are the side effects of chloroquine?
  5. Can chloroquine treat or prevent COVID-19?

1. What is chloroquine?

Chloroquine is an antimalarial drug used both in the treatment and prevention of malaria. It is sold under the brand name Aralen, among others, and is available as a generic drug. It comes in the form of a tablet that is taken orally.

In some parts of the world, particularly in Africa, chloroquine has become less effective in preventing and treating malaria as certain malaria parasites have developed resistance to the drug. However, it is still common and effective in several regions.

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Along with other antimalarials, such as hydroxychloroquine, chloroquine is used to ease the symptoms of autoimmune conditions, including rheumatoid arthritis and lupus erythematosus.

Early lab tests and small, observational studies have also found that chloroquine is potentially effective in treating COVID-19, the disease caused by the 2019 novel coronavirus (SARS-CoV-2). At the time of writing, trials are ongoing to provide greater evidence regarding the safety and efficacy of chloroquine to treat COVID-19.

2. What is chloroquine used for?

Malaria

The use of chloroquine to treat and prevent malaria has changed over time due to certain types of malaria parasites developing a resistance to the drug in particular parts of the world.

The deadliest malaria parasite, Plasmodium falciparum (P. falciparum), is believed to be largely resistant to chloroquine in most parts of the world. P. falciparum is the most prevalent malaria parasite in Africa. In most cases, alternative options (such as artemisinin-based combination therapies (ACTs)) are first-line treatments.

Chloroquine may still be used to treat uncomplicated (not severe) cases of malaria caused by P. falciparum in some parts of the world, including much of Central America. It is often prescribed in combination with another drug, primaquine.

Chloroquine is also used to treat malaria caused by Plasmodium vivax (P. vivax), the second most common malaria parasite, in many parts of the world (including the Americas, parts of Africa, South-East Asia, the Western Pacific, and the Eastern Mediterranean). It may either be used alone or in combination with one or more other drugs. Despite chloroquine being largely effective in treating P. vivax, there are reports of drug resistance in some parts of the world.

Chloroquine may also be used to treat malaria caused by less common parasites, Plasmodium malariae (P. malariae), and Plasmodium ovale (P. ovale).

Drug resistance is an ongoing battle in the prevention and treatment of malaria. Researchers have investigated the possibility that reduced use of chloroquine may be leading to a reduction in drug resistance (particularly concerning the P. falciparum parasite), which could make it a more effective treatment once again. However, it is not yet clear whether that is the case.

Malaria treatment is a particularly changeable area of medicine. The World Health Organization releases an annual malaria report, which contains the latest information regarding treatment.

Extraintestinal Amebiasis

Amebiasis is an infection of the intestines caused by a parasite called entamoeba histolytica, which can cause symptoms such as diarrhea and stomach pains. Although not common, amebiasis can spread to other parts of the body, which is called extraintestinal amebiasis (literally meaning amebiasis outside of the intestines).

Chloroquine can be used to treat extraintestinal amebiasis, usually in combination with an effective intestinal amebicide. In particular, chloroquine has been found effective in treating hepatic amebiasis (amebiasis of the liver).

Rheumatoid Arthritis & Lupus Erythematosus

Chloroquine, along with other antimalarial drugs, such as hydroxychloroquine and quinacrine, has been found effective in treating symptoms of rheumatoid arthritis (RA) and/or lupus erythematosus (LE). These include:

  • Muscle and joint pain
  • Skin rashes
  • Pericarditis (inflammation of the lining of the heart)
  • Pleuritis (inflammation of the lining of the lungs)
  • Fatigue
  • Fever

Hydroxychloroquine is used more commonly than chloroquine, as it is associated with less severe side effects. In particular, chloroquine is believed to be more toxic and poses a greater risk of irreversible eye damage than hydroxychloroquine. However, chloroquine may be used in certain circumstances.

A key benefit of antimalarials in the treatment of RA and LE is that they do not suppress the immune system in the way other drugs do. Antimalarials are often used in combination with other drugs, such as corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs).

Antimalarial drugs may also be used to treat scleroderma, pemphigus, lichen planus, polymyositis, sarcoidosis, and porphyria cutanea tarda.

3. Are chloroquine and hydroxychloroquine the same?

Chloroquine and hydroxychloroquine are similar in several ways. Both are derived from the quinoline molecule, both are antimalarial, and both are used to treat conditions such as rheumatoid arthritis and lupus erythematosus.

The most significant difference between the two compounds is widely accepted to be their toxicity levels. Chloroquine is believed to be significantly more toxic than hydroxychloroquine and is more likely to lead to serious side effects. In particular, ocular toxicity is believed to increase the risk of severe and irreversible eye damage, particularly with long-term use. This is why hydroxychloroquine is preferred for patients who are likely to take the drug for life, such as those living with lupus erythematosus.

Additionally, the greater toxicity of chloroquine increases the risk of overdosing, which can be fatal.

4. What are the side effects of chloroquine?

Chloroquine is usually well tolerated. However, it is associated with more severe side effects than hydroxychloroquine, especially when used for long term treatment.

You should contact your doctor or seek medical help immediately if you experience any of the following symptoms while taking chloroquine:

  • Eye & vision problems, including seeing flashes and streaks of light, blurred vision, or difficulty reading or seeing
  • Hearing loss or ringing in your ears
  • Severe dizziness
  • Fast, slow, or irregular heartbeat
  • Breathing difficulties
  • Vomiting
  • Severe stomach pain or cramping
  • Muscle weakness
  • Seizures
  • Severe depression or other mental health issues
  • Twitching or uncontrolled movements
  • A worsening of skin conditions, such as skin rashes, hives, or itching
  • Signs of liver disease, such as yellowing skin and eyes, stomach and abdominal pains, and dark urine
  • Signs of serious infection, such as high fever, chills, and a persistent sore throat

Other side effects may occur as your body gets used to the medication. These may not require immediate medical attention if they are not severe, but you should speak to your doctor about them if you are concerned, if they are persistent, or they worsen. Such side effects include:

  • Hair loss
  • Increased skin sensitivity to sunlight
  • Headache
  • Loss of appetite
  • Upset stomach
  • Diarrhea

Allergic reactions to chloroquine are rare. Nonetheless, signs of a serious allergic reaction should be treated as a medical emergency. They include:

  • Skin rash – for example itchy, red, or swollen skin
  • Wheezing
  • Tightness in the chest or throat
  • Trouble breathing or talking
  • Swollen mouth, face, lips, tongue, or throat

This is not a complete list of the possible side effects of chloroquine. For more information, you should speak to your doctor or read the patient information label.

5. Can chloroquine treat or prevent COVID-19?

Chloroquine and hydroxychloroquine (which you can read about in question 3: Are chloroquine and hydroxychloroquine the same?) have been touted as potentially effective drugs to treat COVID-19, the disease caused by the novel coronavirus (called SARS-CoV-2).

Use of Hydroxychloroquine & Chloroquine to Treat COVID-19 in the USA

On March 28, 2020, the FDA issued an Emergency Use Authorization (EUA) “for emergency use of oral formulations of chloroquine phosphate and hydroxychloroquine sulfate for the treatment of COVID-19.” The EUA authorizes the use of the drugs to treat adolescent and adult patients weighing 50 kg or more, who are hospitalized, and for whom participation in a clinical trial is not available or feasible. German pharmaceutical company, Sandoz, has donated 30 million doses of hydroxychloroquine to the US Strategic National Stockpile, while Bayer has donated 1 million doses of chloroquine.

EUAs are issued by the FDA to help the US health service combat immediate chemical, biological, radiological or nuclear warfare (CBRN) threats.

The FDA’s emergency authorization comes in light of small, observational studies (including a well-publicized study from France) producing promising results. Lab studies have also shown promising results.

In the French study, a combination of hydroxychloroquine and azithromycin produced positive outcomes in a cohort of 80 patients, providing treatment was provided before the patients were in a serious and irreversible condition.

The French study is one of several to show promising results for the use of existing drugs (including several for chloroquine and hydroxychloroquine) in treating COVID-19. The benefit of repurposing existing drugs is that their safety profile is well established.

However, the evidence is not conclusive and not all of the studies so far conducted have produced consistent results. Typical clinical trials usually take years to perform, something that is not possible in the current situation. Additionally, some experts have questioned the methods used in several studies. Regarding chloroquine and hydroxychloroquine specifically, experts have also warned about the serious side effects the drugs can have, including causing an abnormal heartbeat (arrhythmia), which can lead to a heart attack, and permanent eye damage. The Mayo Clinic has also warned of the possibility of drug induced-sudden cardiac death (DI-SCD).

In short, chloroquine and hydroxychloroquine might help treat COVID-19 but come with significant risks. The FDA considers the potential benefits to outweigh the risks, hence the issuing of the EUA.

Use of Hydroxychloroquine & Chloroquine to Treat COVID-19 Outside of the USA

In the UK, at the time of writing, the government maintains its position that chloroquine and hydroxychloroquine should only be used to treat COVID-19 in clinical trials until more conclusive evidence is available.

Canada is also yet to authorize the use of the drugs. In Australia, pharmacists were urged in a letter from The Pharmaceutical Society of Australia to refuse to fill prescriptions for hydroxychloroquine unless there was a genuine and authorized need.

The executive director of the World Health Organization’s health emergencies program, Dr. Mike Ryan, said on Monday, March 30, 2020, that although some drugs had shown early promise in the treatment of COVID-19, “there’s no proven effective therapeutic or drug” at the moment.

However, there are reports of the drugs being used in other countries, including France and Italy. You should check your local health authority to find out the latest treatment guidelines in your country or region.

What Should You Do?

Under no circumstances should you self-medicate with hydroxychloroquine or chloroquine. The FDA’s EUA explicitly states that the drugs should only be used to treat COVID-19 patients in hospital and treatment must be administered by a healthcare professional. You should never take prescription drugs not prescribed to you or for the purpose prescribed.

The reported stockpiling of these drugs can have other consequences. In the UK, hydroxychloroquine is the primary treatment for 90% of people living with lupus. A shortage of the drug can put those people at risk, as many alternative treatments have immunosuppressive mechanisms of action, which can increase one’s susceptibility to COVID-19.

Additionally, under no circumstances should you take any commercially available products containing hydroxychloroquine or chloroquine. It has been widely reported that a man died, and his wife hospitalized after they took a product intended to treat disease in aquarium fish that contained chloroquine phosphate. The FDA a letter reiterating that such products are not interchangeable with human drugs.

You should follow your health authority’s guidelines on how to protect yourself from COVID-19 and help reduce the spread of infection. Similarly, if you think you may have COVID-19, follow the instructions provided by your health authority.

Please note: The 2019 novel coronavirus pandemic is a rapidly evolving situation. While we make every effort to ensure the information in this article is accurate and up to date, it should not be used as a substitute for official information.


The content on this page is provided for informational purposes only. If you have any questions or concerns about your treatment, you should talk to your doctor, pharmacist, or healthcare professional. This is particularly important if you are taking multiple medications or have any existing medical conditions.

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