Avloclor (Chloroquine)

How does it work?

Avloclor tablets contain the active ingredient chloroquine phosphate, which is an antimalarial medicine, though it also has other uses, for example, in treating the autoimmune diseases rheumatoid arthritis and lupus erythematosus.

Malaria is a potentially fatal disease caused by various types of single-celled (protozoan) parasites known as Plasmodium. Plasmodium are carried by mosquitoes and injected into the bloodstream during a bite from an infected mosquito. Once in the blood, the parasites travel to the liver, where they multiply. The parasites are then released back into the bloodstream where they invade the red blood cells and multiply again. An actual attack of malaria develops when the red blood cells burst, releasing a mass of parasites into the bloodstream. The attacks do not begin until a sufficient number of blood cells have been infected with parasites.

Chloroquine works by attacking the parasites once they have entered the red blood cells. It kills the parasites and prevents them from multiplying further.

It is not fully understood how chloroquine kills the parasites, but it is thought to work by blocking the action of a chemical that the parasites produce to protect themselves once inside the red blood cells. When inside the red blood cells, the malaria parasites digest the oxygen carrying pigment haemoglobin that is found in these cells. This divides the haemoglobin into two parts; haem and globin, and the haem part is toxic to the malaria parasite. To prevent itself from being damaged by haem, the malaria parasite produces a chemical that converts haem into a compound that is not toxic to them. Chloroquine blocks the action of this chemical. This causes the levels of the toxic haem to rise, thus killing the malaria parasites.

Chloroquine can be used both to prevent and to treat malaria. For prevention it is usually taken in combination with another antimalarial medicine called proguanil. However, the malaria parasite is resistant to these medicines in certain areas of the world, and it is important to check with your pharmacist which medicines are currently recommended to prevent malaria in the country you are travelling to. You can also check in the travel section of this site.

If chloroquine is recommended for prevention it should be started a week before travel to the malarious region. It should then be taken throughout the stay, so that if you are bitten by an infected mosquito, there will be medicine in your blood to prevent malaria developing. Chloroquine should be continued for a further four weeks after leaving the malarious area, so that there is still medicine in the blood to kill any remaining parasites released from the liver into the red blood cells during this time.

Higher doses than those used for preventing malaria are used to treat malaria infection. Chloroquine may be given by injection to treat malaria, if administration by mouth is not possible. However, chloroquine is no longer recommended for treating falciparum malaria (the most serious kind, caused by a type of malaria parasite called Plasmodium falciparum), because there is widespread resistance of the Plasmodium falciparum parasite to chloroquine.

Chloroquine is also active against other types of protozoa, including one called Entamoeba histolytica (which causes amoebic dysentry). Metronidazole is the drug of choice for infections with this parasite, but chloroquine can be used to treat liver infections (amoebic hepatitis) if metronidazole is not available.

Chloroquine also has anti-inflammatory activity and is sometimes used in high doses to treat the autoimmune diseases rheumatoid arthritis, systemic lupus erythematosus, and discoid lupus erythematosus. In these diseases, the body's immune system is overactive and causes inflammation that results in the disease symptoms. Chloroquine suppresses the inflammation and the disease process.

In rheumatoid arthritis, chloroquine is known as a disease-modifying antirheumatic drug (DMARD). It doesn't have an immediate effect, but requires four to six months of treatment for a full response. If there is no real benefit on the disease after taking this medicine for six months, your doctor will usually ask you to stop taking it and try a different DMARD.

What is it used for?

  • Prevention of malaria (chloroquine can be bought from pharmacies without a prescription for this purpose; it is not prescribable on the NHS for preventing malaria)
  • Treatment of malaria
  • Infection of the liver with Entamoeba histolytica (hepatic amoebiasis or amoebic hepatitis)
  • Inflammatory disease of the joints (rheumatoid arthritis)
  • Systemic lupus erythematosus (SLE) and discoid lupus erythematosus (DLE)


  • To prevent malaria this medicine should be taken once a week, on the same day each week, starting one week before travelling to the malarious area. It should be taken regularly thoughout the stay and continued for four weeks after leaving the malarious area.
  • To prevent malaria it is important that you take this medicine regularly and try not to forget a dose. You may find it helpful to make a note of the day you take your dose in your diary or calender. You must still take precautions to avoid being bitten by mosquitos, such as using mosquito repellants and sleeping under mosquito nets. This is particularly important if you have vomiting or diarrhoea, as this could affect the absorption of this medicine from the gut. If you fall ill within one year of your return, and especially if within three months of your return, you should consult your doctor immediately and let him know that you have visited a country where malaria is endemic.
  • This medicine may cause visual disturbances when you first start taking it. If affected you should use caution when driving or operating machinary.
  • This medicine can sometimes cause eye problems when used for long-term treatment (eg for rheumatoid arthritis) . For this reason, you should have an eye examination before you start long-term treatment and then regularly every three to six months while you are taking the medicine. Stop taking this medicine and seek medical advice immediately if you notice any deterioration in your vision that lasts for longer than 48 hours. (These precautions also apply to people who have been taking chloroquine on a continuous basis every week for more than three years to prevent malaria.)
  • People taking this medicine for long periods of time should also have regular blood tests to monitor the amounts of the different types of blood cells in their blood. This is because chloroquine may rarely cause a decrease in the normal amounts of blood cells in the blood. Consult your doctor if you experience any of the following symptoms while taking this medicine: unexplained bruising or bleeding, purple spots, sore throat, mouth ulcers, high temperature (fever), feeling tired or general illness. Your doctor may want to take a blood test to check your blood cells.

Use with caution in

  • Elderly people
  • Liver disease
  • Kidney disease
  • History of epilepsy
  • Disorders affecting the brain, nerves or spinal cord (neurological disorders)
  • Abnormal muscle weakness (myasthenia gravis)
  • Severe gut disorders
  • Blood disorders
  • Rare hereditary blood disorders called porphyrias
  • Lack of the enzyme G6PD in the blood (G6PD deficiency)
  • Psoriasis

Not to be used in

  • Allergy to any ingredient.
  • People with a history of epilepsy should not take this medicine for preventing malaria.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • High doses of this medicine during pregnancy, eg to treat rheumatoid arthritis, may be harmful to a developing baby and should only be used if the potential benefits outweigh the risks to the foetus. Seek medical advice from your doctor. The situation is different for low doses used to prevent malaria, and this medicine has a long history of safe use for preventing malaria during pregnancy. However, it should only be used after seeking medical advice from a doctor. Pregnant women who cannot avoid travel to malarious areas must take effective measures to prevent malaria and be diligent with measures to avoid mosquito bites.
  • This medicine passes into breast milk, but in doses taken to prevent malaria is not harmful to a nursing infant. However, the amount of medicine that passes into the milk is not sufficient to prevent malaria in the nursing infant and the child will also need to be given antimalarial medicine. You should seek medical advice from your doctor or pharmacist with regards to what medicine and what dose to give. If you are taking this medicine for reasons other than preventing malaria, you should consult your doctor before breastfeeding. Breastfeeding is not recommended if you are taking this medicine for rheumatoid arthritis.

Label warnings

  • Do not take indigestion remedies at the same time of day as this medication.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Disturbances of the gut such as diarrhoea, nausea, vomiting or abdominal pain
  • Headache
  • Skin rashes
  • Itching (pruritus)
  • Low blood pressure (hypotension), this might make you feel dizzy
  • Visual disturbances
  • Loss of hair colour
  • Hair loss (alopecia)
  • Fits (convulsions)
  • Disturbance in the normal numbers of blood cells in the blood
  • Damage to the retina of the eye (long-term use)
  • Discolouration of skin, nails, or mucous membranes, eg inside of mouth
  • Hearing distubances, eg ringing in the ears (tinnitus) or hearing loss
  • Anxiety, confusion, hallucinations or strange or abnormal thoughts
  • Weakening of muscles
  • Weakening of the heart muscle (long-term use at high doses)
  • Changes in the electrical signals in the heart (seen on an ECG)
  • Liver disorders

When chloroquine is taken in low doses to prevent malaria it is generally well tolerated and any side effects that are experienced are not normally of a serious nature.

Prolonged use at high doses, eg for treating rheumatoid arthritis, is more likely to be associated with side effects, though you still may not experience any.

The side effects listed above may not include all of the side effects reported by the drug's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

Antacids (used to treat indigestion and heartburn) and kaolin reduce the absorption of chloroquine from the gut, which may mean the full dose is not absorbed into the body. To avoid this, antacids and kaolin should not be taken in the two to three hours before or after taking your chloroquine dose.

Cimetidine may prevent the breakdown of chloroquine by the liver and lead to increased levels of chloroquine in the blood. You should avoid taking cimetidine with chloroquine as it may increase the risk of side effects. If you do take cimetidine in combination with chloroquine, let your doctor or pharmacist know if you experience any new or increased side effects.

Chloroquine may increase the blood level of the following medicines, which may result in an increased risk of their side effects:

  • ciclosporin
  • digoxin.

There may be a risk of abnormal heart rhythms if chloroquine is taken in combination with any of the following medicines:

  • medicines for abnormal heart rhythms, eg amiodarone, quinidine
  • the antihistamines terfenadine and astemizole
  • halofantrine
  • mefloquine
  • certain antipsychotics, eg chlorpromazine, thioridazine
  • certain antidepressants, eg imipramine, amitriptyline, maprotiline
  • moxifloxacin.

There may be an increased risk of convulsions (fits) if chloroquine is taken with mefloquine.

Chloroquine may reduce the effectiveness of the rabies vaccine. If you need to have a rabies vaccine you should have it before you start taking chloroquine.

Chloroquine may reduce the effectiveness of neostigmine or pyridostigmine for treating myaesthenia gravis.

Other medicines containing the same active ingredient

Chloroquine injection Malarivon syrup Nivaquine

Paludrine/Avloclor is a travel pack for preventing malaria that contains chloroquine in combination with another antimalarial medicine called proguanil.