How does quinine work?

• Quinine is a type of medicine called an antimalarial. You may be given it as quinine sulfate or quinine bisulfate.
• 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.
• Quinine 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 it kills the parasites.
• Quinine is also sometimes used to treat recurrent night-time leg cramps, for instance in people with diabetes or varicose veins. It's thought to prevent muscle cramps by reducing the sensitivity of muscle cells to stimuli that cause them to contract, as well as by prolonging the time it takes for the muscle to contract. Quinine tends to reduce the number and severity of leg cramps, but may not stop them completely.
• It can take up to four weeks of taking quinine before an improvement in leg cramps is seen. You should keep a sleep and cramp diary for a few weeks before you start taking quinine and continue this while you're taking it, to help you monitor whether the medicine is helping. If your cramps don't seem to have improved after four weeks of taking quinine then it should be stopped.

How do I take quinine?

• Quinine tablets can be taken either with or without food. The tablets should be swallowed whole with a drink of water.
• The dose prescribed and how often the medicine needs to be taken depends on whether you are taking it for malaria or leg cramps. Always follow the instructions given by your doctor. These will be printed on the dispensing label your pharmacist has put on the packet of medicine.
• To treat night-time leg cramps in adults, the usual dose is one 200mg or 300mg tablet taken once a day at bedtime.
• If you forget to take a dose of quinine for leg cramps, just leave out the missed dose and take your next dose as usual the next night. Do not take a double dose to make up for a missed dose.
• To treat malaria a dose of quinine is usually taken every eight hours for five to seven days. The dose prescribed will depend on your age, size, severity of the infection and if you have any liver or kidney problems. It's important to follow the instructions given by your doctor and to complete the prescribed course.
• If you forget to take a dose of quinine for malaria, take it as soon as you remember and then space out the rest of the doses for that day over the remainder of the day. Try to always take the correct number of doses per day, but don't take two doses together.
• Quinine may sometimes be given by a drip into a vein to treat malaria in people who are unable to take tablets.

What should I know before taking quinine?

• Do not exceed the dose prescribed by your doctor. Quinine can cause serious, irreversible side effects if you take too much.
• You should tell your doctor if you experience hearing problems, ringing sensations in your ears (tinnitus), headaches, feeling sick, rash or disturbed vision while taking quinine. These can be signs of quinine poisoning and your doctor may ask you to stop taking the medicine or reduce your dose.
• Quinine has several potential side effects that make it unsuitable for long-term use. It should not be taken to prevent malaria. Other antimalarials should be used to prevent malaria.
• If you're taking quinine for leg cramps your doctor will usually ask you to stop taking it for a trial period about every three months to make sure you still need to take it.

Can I take quinine while pregnant or breastfeeding?

• Quinine can potentially cause problems to the developing baby if it is used during pregnancy. It should not be used to treat leg cramps in women who are pregnant. However in the treatment of malaria, which is life-threatening, the risks of the medicine will usually be outweighed by the life-saving effect of the treatment. Ask your doctor for further advice about taking this medicine if you are pregnant.
• Quinine passes into breast milk. It is not known to be harmful to a nursing infant, however it should only be used during breastfeeding if the potential benefits outweigh any potential risks to the baby. It should not be used in mothers whose babies are glucose-6-phosphate dehydrogenase (G6PD) deficient. Make sure your doctor knows if you are breastfeeding before you take this medicine.

What are the possible side effects of quinine?

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 quinine. Just because a side effect is stated here doesn't mean that all people using this medicine will experience that or any side effect.

• Rash. Tell your doctor if you get this.
• Nausea. Tell your doctor if you get this.
• Sensation of ringing, or other noise in the ears s(tinnitus). Tell your doctor if you get this.
• Hearing problems. Tell your doctor if you get this.
• Headache. Tell your doctor if you get this.
• Visual disturbances, such as blurred vision, problems with colour vision and narrowed field of vision. Tell your doctor if you get this.
• Low blood glucose level (hypoglycaemia).
• Abdominal pain.
• Diarrhoea.
• Confusion.
• Agitation.
• Spinning sensation.
• Flushing.
• Increased sensitivity of the skin to sunlight (photosensitivity).
• Allergic reactions such as skin rashes, narrowing of the airways and breathing difficulties or swelling of lips, face or tongue (angioedema). Stop taking quinine and consult your doctor if you think you've had an allergic reaction to it.
• Problems with your blood cells or blood clotting. Tell your doctor if get any unexplained bruising or bleeding while you're taking quinine.
• Kidney failure.
• Muscle weakness.
• Abnormal heart rhythms (arrhythmias).

Can quinine affect other medicines?

It's important to tell your doctor or pharmacist what medicines you're already taking, including those bought without a prescription and herbal medicines, before taking quinine. Similarly, check with your doctor or pharmacist before taking any new medicines with quinine, to make sure that the combination is safe.

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

• medicines for abnormal heart rhythms, eg amiodarone, quinidine (combination should be avoided)
• the antihistamines terfenadine and astemizole
• artemether with lumefantrine (Riamet)
• citalopram (combination should be avoided)
• droperidol (combination should be avoided)
• escitalopram (combination should be avoided)
• halofantrine
• haloperidol (combination should be avoided)
• mefloquine
• moxifloxacin (combination should be avoided)
• pimozide (combination should be avoided)
• Riamet (artemether with lumefantrine) (combination should be avoided)
• risperidone
• saquinavir (combination should be avoided)
• thioridazine (combination should be avoided)

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

• amantadine
• digoxin
• flecainide
• mefloquine (increased risk of convulsions if quinine used with mefloquine).

Protease inhibitors for HIV infection, such as darunavir, fosamprenavir, indinavir, nelfinavir and atazanavir, can increase the blood level of quinine, which may increase the risk of its side effects.

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

Rifampicin may increase the breakdown of quinine by the body and so could make it less effective.

Quinine may enhance the anti-blood-clotting effect of the anticoagulant medicine warfarin.

Quinine could inactivate the oral typhoid vaccine (Vivotif) and make it ineffective, so you shouldn't take this vaccine while you're taking quinine.

References:

https://pubchem.ncbi.nlm.nih.gov/compound/13119

https://www.medicines.org.uk/emc/medicine/24467

https://www.medicines.org.uk/emc/medicine/18143

https://patient.info/medicine/quinine-for-leg-cramps

http://www.netdoctor.co.uk/medicines/infections/a7438/quinine-sulfate/

https://www.drugs.com/uk/quinine-sulphate-tablets-bp-300mg-leaflet.html