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Prescription tablet taken by mouthAn antimalarial and amebicidal medicine of the 4-aminoquinoline type

Chloroquine Phosphate

Chloroquine phosphate · Say it: KLOR-oh-kwin FOS-fate

A prescription tablet used to treat certain types of malaria and a parasite infection called extraintestinal amebiasis, and to prevent malaria in some areas. It carries serious heart, eye, nerve, and blood sugar warnings.

Brand names: Chloroquinum Phos.

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Used for

Treatment of uncomplicated malaria caused by susceptible strains of P. falciparum, P. malariae, P. ovale, and P. vivax

Comes as

500 mg tablets (equivalent to 300 mg chloroquine base), white, round, film-coated, debossed 'CN 500'

Common side effects

The label lists these reactions as reported after the medicine was approved, but says it is not always possible to estimate how often they happen: nausea, vomiting, diarrhea, stomach cramps, loss of appetite, headache, itching, and hair loss or bleaching of hair color, Mild and temporary headache

Key facts
Generic nameChloroquine phosphate
Brand namesChloroquinum Phos.
Type of medicineAn antimalarial and amebicidal medicine of the 4-aminoquinoline type
How it is soldPrescription tablet taken by mouth
Comes as500 mg tablets (equivalent to 300 mg chloroquine base), white, round, film-coated, debossed 'CN 500'
Routeoral
Boxed warningNo
Label date2026-07-02

💊 What is Chloroquine Phosphate used for?

  • Treatment of uncomplicated malaria caused by susceptible strains of P. falciparum, P. malariae, P. ovale, and P. vivax
  • Prevention (prophylaxis) of malaria in geographic areas where chloroquine resistance is not present
  • Treatment of extraintestinal amebiasis

How it works

How it is usually taken

  • The tablets are taken by mouth. The label says the dose is often expressed as the amount of chloroquine base, and that children's doses are usually calculated by body weight. For prevention, the label describes one dose once a week on exactly the same day each week. For treatment, it describes a series of doses over several days. The label says the medicine should not be used for complicated malaria. Follow the exact schedule given by your prescriber or pharmacist.

Comes as

  • 500 mg tablets (equivalent to 300 mg chloroquine base), white, round, film-coated, debossed 'CN 500'

⚠️ Chloroquine Phosphate side effects

Common side effects

  • The label lists these reactions as reported after the medicine was approved, but says it is not always possible to estimate how often they happen: nausea, vomiting, diarrhea, stomach cramps, loss of appetite, headache, itching, and hair loss or bleaching of hair color
  • Mild and temporary headache

Get medical help right away if

  • Get medical help right away if you have blurred vision, trouble focusing, trouble reading with words seeming to disappear, seeing half of an object, or other changes in your vision. The label says these eye changes can be irreversible.
  • Get medical help right away if you have fainting, a very slow or irregular heartbeat, chest discomfort, or new swelling. The label warns of heart muscle disease, rhythm problems, and QT prolongation, which can be fatal.
  • Get medical help right away if you have shakiness, sweating, confusion, or loss of consciousness, which can be signs of severe low blood sugar.
  • Get medical help right away if you have new muscle weakness, numbness, tingling, or trouble walking.
  • Get medical help right away if you have a skin rash with blistering, peeling, mouth sores, or fever, or swelling of the face, lips, or throat.
  • Get medical help right away if you have seizures, hearing loss, ringing in the ears, or sudden changes in mood, thinking, or behavior, including thoughts of suicide.
  • Get medical help right away if you have fever, sore throat, unusual bruising or bleeding, or signs of liver trouble such as yellowing of the skin or eyes.
  • Get medical help right away if you have signs of hemolytic anemia, such as dark urine, paleness, or unusual tiredness. The label says this can happen in people with G6PD deficiency.

🛑 Who should not take Chloroquine Phosphate, and who should be careful

The label says not to take it if

  • You have retinal or visual field changes of any cause, if the medicine is being used for any purpose other than acute malaria.
  • You have a known allergy or hypersensitivity to 4-aminoquinoline compounds.
  • The label says not to use it to treat complicated malaria, such as cerebral malaria or cases with high parasite levels or complications.
  • The label says not to use it to prevent malaria in areas where chloroquine resistance occurs.

Tell your doctor before taking it if

  • Tell your prescriber or pharmacist about any heart disease, past irregular heartbeat, slow heart rate, or low potassium or magnesium levels, because the label says to use caution in these cases.
  • Tell your prescriber if you have diabetes or take diabetes medicines, because the label warns about severe low blood sugar.
  • Tell your prescriber if you have eye or vision problems, kidney problems, or a condition called G6PD deficiency.
  • Tell your prescriber about all other medicines you take, especially medicines that can prolong the QT interval.
  • The label says that for long-term use, muscle strength and reflexes should be checked from time to time.
  • The label says to check whether chloroquine is appropriate for the region you plan to visit, using the CDC malaria resources it lists.

🔀 Chloroquine Phosphate with other medicines, food and alcohol

The label says to discuss these with your doctor or pharmacist

  • Medicines that prolong the QT interval: the label says the risk of heart rhythm problems is higher when chloroquine is given with these drugs.
  • Antidiabetic medicines: the label warns that chloroquine can cause severe low blood sugar, with or without these medicines.
  • Tamoxifen: the label names this as a concomitant drug that can increase the risk of retinal damage.
  • 8-aminoquinoline medicines: the label says these are needed alongside chloroquine to treat the liver stage of P. vivax and P. ovale malaria.

Alcohol and food

The label does not say.

🤰 Chloroquine Phosphate in pregnancy and breastfeeding

Pregnancy

The label does not say.

Breastfeeding

The label does not say.

🗓️ Storage, missed doses and taking too much

Storage

Store at 20 to 25 °C (68 to 77 °F), with brief excursions permitted between 15 and 30 °C (59 to 86 °F). The label says to keep the tablets in a tight, light-resistant container.

If a dose is missed

The label does not say.

If too much is taken

The label says chloroquine is absorbed very quickly and completely, and that toxic doses can be fatal. It says even a relatively small amount may be fatal in children, and that toxic symptoms can start within minutes. Symptoms may include nausea, vomiting, headache, drowsiness, vision changes, collapse, seizures, and dangerous heart rhythm problems that can lead to cardiac arrest. The label states that immediate medical attention is required.

🗒️ Questions to ask about Chloroquine Phosphate

🎯 Check what you understood

1. According to the summary, which kind of malaria should chloroquine NOT be used to treat?

2. What does the label say about eye-related warnings?

3. Why does the label say chloroquine may not prevent relapses of vivax or ovale malaria?

❓ Chloroquine Phosphate: frequently asked questions

What is chloroquine phosphate used for?

The label says it is used to treat uncomplicated malaria from susceptible strains, to prevent malaria in areas without chloroquine resistance, and to treat extraintestinal amebiasis.

Can chloroquine affect my heart?

Yes. The label warns of fatal and life-threatening cardiotoxicity, including cardiomyopathy, arrhythmias, and QT prolongation, and says to use caution in people with heart disease.

Can chloroquine cause eye damage?

The label says irreversible retinal damage has been observed in some patients, and that risk factors include longer durations of use and certain other medicines such as tamoxifen.

Can chloroquine lower blood sugar?

Yes. The label says chloroquine has been shown to cause severe hypoglycemia, including loss of consciousness that could be life-threatening, with or without antidiabetic medicines.

Is chloroquine dangerous if too much is taken?

The label says toxic doses can be fatal and that immediate medical attention is required after an overdose. It notes that even a relatively small amount may be fatal in children.

🧪 Tests and reports linked to Chloroquine Phosphate

The label text mentions these. If you have one of these reports, get every line of it explained.

📖 Medical words used on this page

  • Acute vs chronic

    Acute means something started recently or suddenly. Chronic means it has lasted a long time or keeps coming back.

  • Allergic reaction

    An allergic reaction is when the immune system overreacts to something harmless, such as a medicine or food, causing symptoms from a rash to swelling.

  • Anemia

    Anemia means the blood has fewer healthy red blood cells or less hemoglobin than the reference range printed on the report.

  • Antimalarial

    An antimalarial is a medicine used to prevent or treat malaria, and some are also used for conditions such as lupus and rheumatoid arthritis.

  • Arrhythmia

    An arrhythmia is a heartbeat that is too fast, too slow or irregular, because the heart's electrical signals are not working in their usual pattern.

  • Bradycardia

    Bradycardia means a slower-than-usual heart rate. It can be normal in fit people, or a side effect of some medicines.

  • Concomitant

    Concomitant means 'at the same time'; on a medicine label, concomitant use means taking two medicines during the same period.

  • Edema

    Edema is swelling caused by extra fluid trapped in the body's tissues, often in the feet, ankles and legs.

  • Film-coated

    Film-coated means a tablet has a thin outer layer that makes it easier to swallow, masks taste, or protects the medicine inside.

  • G6PD deficiency

    G6PD deficiency is an inherited shortage of an enzyme that protects red blood cells, so some medicines, foods or infections can break them down.

  • Hemolytic anemia

    Hemolytic anemia is a low red blood cell count caused by red cells being destroyed faster than the body can replace them.

  • Hypersensitivity

    Hypersensitivity means the immune system overreacts to something, such as a medicine. It covers allergic reactions from mild rash to severe reactions.

  • Hypoglycemia

    Hypoglycemia means blood sugar (glucose) has dropped too low. It can cause shakiness, sweating and confusion, and severe cases need urgent help.

  • Hypokalemia

    Hypokalemia means the level of potassium in the blood is lower than expected. Some medicines, like many diuretics, can cause it.

📖 Medical words on this page

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🧩 Similar medicines

  • Primaquine · An antimalarial medicine of the 8-aminoquinoline group, as described in the label
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Source: official FDA drug label (label updated 2026-07-02). Read the full label on DailyMed

MedicDecode explains the official label in plain words. It is not medical advice and does not replace your doctor or pharmacist. Never start, stop or change a medicine because of what you read here.