Chloroquine belongs to the class of medications called antimalarials. This medication is used to treat and prevent attacks of malaria. It works by killing malaria parasites, most likely by damaging their DNA (genetic material). This medication is also used to treat another condition caused by parasites known as extraintestinal amebiasis.

Your doctor may have suggested this medication for conditions other than the ones listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

Prevention of malaria: For adults, the dose of chloroquine is usually 500 mg once a week, taken on exactly the same day every week. To prevent malaria, start taking the tablets 2 weeks before leaving for an area where malaria is a risk and continue taking the tablets for 4 weeks after your return. Children's doses are based on body weight.

Treatment of malaria: For adults, treatment usually begins with a 1 g (1000 mg) dose followed by 500 mg after 6 to 8 hours. This is followed by a single dose of 500 mg on each of 2 consecutive days. This makes for a 3-day total dose of 2.5 g. Children's doses are based on body weight.

Chloroquine may be taken either before or after meals.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by the doctor. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not use chloroquine if you:

• are allergic to chloroquine or any ingredients of the medication
• have visual problems due to chloroquine or similar medications (unless in the treatment of malaria it is decided that the benefits outweigh the risks)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• bleaching of hair or increased hair loss
• blue-black discoloration of skin, fingernails, or inside of mouth
• diarrhea
• difficulty in seeing to read
• headache
• itching
• loss of appetite
• nausea or vomiting
• skin rash
• stomach cramps or pain

Although most of the side effects listed below don’t happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• black, tarry stools
• blood in urine or stools
• convulsions (seizures)
• cough or hoarseness
• eye pain
• feeling faint or lightheaded
• fever or chills
• increased muscle weakness
• lower back or side pain
• mood or other mental changes
• painful or difficult urination
• pinpoint-sized red spots on skin
• ringing or buzzing in ears or any loss of hearing
• sore throat
• unusual bleeding or bruising
• unusual tiredness or weakness

Stop taking the medication and seek immediate medical attention if any of the following occur:

• blurred vision, vision problems, or loss of vision

Symptoms of overdose:

• drowsiness
• headache
• increased excitability

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.

Medical conditions: If you have epilepsy, liver disease, porphyria, psoriasis, or stomach or intestinal disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Visual problems: If you notice any signs of abnormality in your vision (e.g., symptoms such as light flashes and streaks) seek immediate medical attention. If chloroquine is found to be the cause, stop taking it.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and are taking chloroquine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

There may be an interaction between chloroquine and any of the following:

• ampicillin
• antacids that contain aluminum or magnesium
• chlorpromazine
• cimetidine
• cyclosporine
• dapsone
• digoxin
• lanthanum
• mefloquine
• methotrexate
• quinidine
• quinine
• tamoxifen

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.