Quinine belongs to the class of medications known as antimalarials. It is used along with one other medication (usually an antibiotic) to treat certain types of malaria.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. 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.

For treatment of malaria, the average recommended daily adult dose of quinine is 600 mg by mouth, every 8 hours, for 3 to 7 days. Children's doses are calculated according to body weight. Quinine should be taken after meals to reduce the possibility of upset stomach.

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 or dosing schedule 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 your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If more than 4 hours has passed since the missed 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 take this medication if you:

• are allergic to quinine or any ingredients of the medication
• are allergic to quinidine or mefloquine
• have a glucose-6-phosphate dehydrogenase deficiency
• have an irregular heart rhythm called prolonged QT interval
• have a history of blackwater fever and thrombocytopenic purpura (purplish discoloration of skin)
• have low platelet levels (thrombocytopenia)
• have idiopathic thrombocytopenia purpura (ITP) and thrombotic thrombocytopenic
• purpura (TTP)
• have a history of hemolytic uremic syndrome (HUS)
• have myasthenia gravis
• have optic neuritis
• have low levels of the enzyme glucose-6 phosphate dehydrogenase (G-6-PD)

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.

• abdominal or stomach cramps or pain
• diarrhea
• dizziness
• flushing
• headache
• increased sweating
• nausea
• vomiting

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

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

• abnormal heart rhythms (e.g., very fast, slow, or pounding heartbeat)
• ringing or buzzing in ears
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood, bleeding gums, cuts that don't stop bleeding)
• symptoms of low blood sugar (e.g., cold sweat, cool pale skin, headache, fast heart beat, weakness, confusion)
• vision changes (e.g., sensitivity to light, night blindness, blurred vision, eye inflammation, "floaters", change in colour perception)

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

• coma
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• seizures

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 using 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 use this medication.

Abnormal heart rhythms: This medication can cause abnormal heart rhythms. Certain medications (e.g., sotalol, quinidine, chlorpromazine,  pimozide, moxifloxacin, mefloquine, pentamidine, arsenic trioxide, probucol, tacrolimus) can increase the risk of a type of abnormal heart rhythm called QT prolongation, and should not be used in combination with quinine. You are more at risk for this type of abnormal heart rhythm and its complications if you:

• are female
• are older than 65 years of age
• have a family history of sudden cardiac death
• have a history of heart disease or abnormal heart rhythms
• have a slow heart rate
• have congenital prolongation of the QT interval
• have diabetes
• have had a stroke
• have low potassium, magnesium, or calcium levels
• have nutritional deficiencies

If you have heart disease and abnormal heart rhythms, or people are taking certain medications (e.g., verapamil, atazanavir), 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.

Bleeding: Quinine may cause a reduced number of platelets in the blood, which can make it difficult to stop cuts from bleeding. If you notice any signs of bleeding, such as frequent nosebleeds, unexplained bruising, or black and tarry stools, notify your doctor as soon as possible. Your doctor will order routine blood tests to make sure potential problems are caught early.

Diabetes: Quinine causes insulin to be released from the pancreas and may lower blood sugar levels. If you have diabetes, 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. You made need to monitor your blood sugar more closely while taking this medication.

Kidney function: The kidneys are partially responsible for removing this medication from your body. Kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney 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.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, 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. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Myasthenia gravis: Myasthenia gravis is a condition that causes specific muscle weakness. Quinine may cause muscle weakness, worsening the symptoms of myasthenia gravis. People with myasthenia gravis should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: Quinine may cause birth defects and it can cause complications to the pregnancy. Women who are pregnant are more likely to experience noticeable low blood sugar levels. It should be used during pregnancy only when required to treat a severe case of life-threatening malaria.

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

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

• aliskiren
• alpha blockers (e.g., alfuzosin, doxazosin, tamsulosin)
• amiodarone
• androgens (e.g., testosterone)
• angiotensin-converting enzyme inhibitors (ACEIs; captopril, ramipril)
• angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan, losartan)
• antacids (e.g., aluminum hydroxide, calcium carbonate, magnesium hydroxide)
• antihistamines (e.g., bilastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine)
• antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apalutamide
• "azole" antifungals (e.g., itraconazole, ketoconazole, voriconazole)
• beta-adrenergic blockers (e.g., carvedilol, metoprolol, propranolol, nadolol, sotalol, timolol)
• beta-2 agonists (e.g., indacaterol, olodaterol, salmeterol)
• bosentan
• buprenorphine
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• cancer medications (e.g., daunorubicin, doxorubicin, etoposide, idarubicin, irinotecan, methotrexate, paclitaxel, tamoxifen, temsirolimus, vinblastine, vincristine)
• carbamazepine
• cimetidine
• cobicistat
• colchicine
• conivaptan
• cyclosporine
• dabigatran
• dapsone
• diabetes medications (e.g., acarbose, canagliflozin, glyburide, linagliptin, lixisenatide, metformin, rosiglitazone)
• digoxin
• disopyramide
• domperidone
• donepezil
• dronedarone
• enzalutamide
• fingolimod
• flecainide
• grapefruit juice
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• leuprolide
• lanreotide
• lithium
• loperamide
• macrolide antibiotics (e.g., azithromycin, clarithromycin, erythromycin)
• mefloquine
• methadone
• metoclopramide
• metronidazole
• mifepristone
• mirtazapine
• neuromuscular blockers (e.g., succinylcholine, pancuronium)
• modafinil
• monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, phenelzine, rasagiline, selegiline, tranylcypromine)
• octreotide
• pasireotide
• pentamidine
• phenobarbital
• phenytoin
• primidone
• primaquine
• procainamide
• propafenone
• protein kinase inhibitors (e.g., dasatinib, imatinib, sunitinb)
• quinidine
• quinolone antibiotics (e.g., ciprofloxacin, norfloxacin, ofloxacin)
• rifabutin
• rifampin
• St. John's wort
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline)
• serotonin antagonists (anti-emetic medications; e.g., granisetron, ondansetron)
• silodosin
• sirolimus
• sodium bicarbonate
• solifenacin
• somatostatin acetate
• "statin" anti-cholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
• sulfonamide antibiotics ("sulfas"; e.g., sulfisoxazole, sulfamethoxazole)
• tacrolimus
• tamoxifen
• tetrabenazine
• tetracycline
• theophyllines (e.g., aminophylline, oxtriphylline, theophylline)
• trazodone
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• vardenafil
• warfarin

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 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.