How quinine works
Quinine is a natural ingredient from the bark of the quinaberry tree and has antiparasitic, antipyretic and muscle-relaxing properties. Furthermore, its bitter taste is used to make bitter drinks such as tonic water.
Quinine acts at different sites in the body. For example, it leads to muscle relaxation through various mechanisms.
In addition, quinine affects the distribution of calcium in the muscle, which is also important for contraction. In sum, this derives its use in severe calf cramps.
Quinine also has antipyretic and analgesic effects. Extracts from the bark of the quinine tree were used for this purpose very early as a medicine.
To obtain protein building blocks (amino acids), they break down the oxygen-transporting hemoglobin in the erythrocytes. The decomposition product is the iron-containing dye heme, which is toxic to malaria pathogens in its free form.
In the past, quinine was also used as a labor-inducing agent. In the meantime, however, more effective and better tolerated agents are available for this purpose.
The misuse of high doses of quinine as an abortifacient not infrequently leads to fatal kidney failure.
Absorption, degradation and excretion
After about half a day, half of the absorbed amount of active substance is excreted again by the kidneys, with a large part being metabolized by the liver beforehand.
When is quinine used?
Only one quinine preparation is approved as a finished drug in Germany, which is used for the prevention and therapy of nocturnal calf cramps. The tablets contain the active ingredient in the form of quinine sulfate (the sulfuric acid salt of quinine, which is more soluble in water).
In Switzerland, on the other hand, quinine in tablet form is approved as a finished drug for the treatment of complicated malaria tropica. In Austria, neither preparations against calf cramps nor against malaria are on the market. However, the active ingredient can also be ordered here or manufactured in the (hospital) pharmacy.
How quinine is used
To treat nocturnal muscle cramps, one tablet containing a dose of 200 milligrams of quinine is taken after dinner for mild symptoms. For moderate to severe symptoms, two tablets are taken in the evening – one after dinner, one before bedtime.
The duration of therapy should not exceed two to three weeks, as the active substance can accumulate in the body.
If necessary, quinine is combined with other drugs such as doxycycline or clindamycin for better efficacy.
Intravenous therapy for malaria infections is individualized based on the severity of the infection and other criteria and is determined by the physician.
What are the side effects of quinine?
Most of the side effects are dose-dependent and disappear after quinine therapy is discontinued.
What should be considered when taking quinine?
Contraindications
Quinine should not be taken by:
- known hypersensitivity or allergy to quinine or quinine-containing beverages.
- glucose-6-phosphate dehydrogenase deficiency (congenital enzyme deficiency)
- Myasthenia gravis (hereditary muscle disease)
- Tinnitus
- Pre-damage of the optic nerve
- bradycardia (slowed heartbeat) or other cardiac arrhythmias
- severe heart failure (cardiac insufficiency)
- congenital or acquired QT interval prolongation
- concomitant use of drugs that can prolong the QT interval
Drug interactions
The simultaneous use of other active substances that lead to a change in the heart rhythm (especially to a so-called QT time prolongation, i.e. an inhibition of the conduction of impulses at the heart) is not recommended.
These include drugs against cardiac arrhythmias (antiarrhythmics), drugs against psychoses (antipsychotics/neuroleptics), some antidepressants, antibiotics, allergy drugs (antihistamines) and strong painkillers from the group of opioids.
Quinine is primarily degraded via the CYP3A4 enzyme. Drugs or foods that interact with the CYP3A4 enzyme can therefore enhance or weaken the effects and side effects of quinine.
As a general rule, anyone wishing to take other medicines in addition to quinine, or who has been prescribed new medicines, should inform their doctor or pharmacist beforehand to be on the safe side.
Age restriction
In elderly patients with reduced renal function, the dose may need to be adjusted.
Pregnancy and Lactation
Because quinine can cross the placental barrier, it should not be used during pregnancy. Only use in malaria is recommended in the absence of alternatives.
Quinine passes into breast milk. Experience with breastfeeding women is limited, but does not indicate a significant risk to the infant. Breastfeeding may continue during short-term malaria therapy. For other indications, quinine is not recommended during breastfeeding.
How to obtain medicines containing quinine
Quinine is subject to prescription in Germany, Austria and Switzerland and can only be obtained from pharmacies with a valid prescription.
Quinine has long been used by the indigenous population of Peru, the Quechua, against trembling at lower temperatures. For this purpose, the ground bark of the cinchona tree was mixed with sweetened water and drunk.
Increasing resistance of the malaria pathogen to other agents has led to quinine being used more frequently again for complicated malaria.
