Quinine is a chemical compound found in the bark of the cinchona tree. Quinine is used medicinally mainly for the therapy of malaria, especially malaria tropica. In addition, it is sometimes used for the prophylaxis and therapy of muscle cramps and in preparations to relieve the symptoms of flu-like infections. In addition, it is also used as a bittering agent in some foods.
What is quinine?
Quinine is a natural substance found in cinchona bark, the bark of the cinchona tree. Quinine is a chemical compound classified in the group of quinoline alkaloids. Quinine, which has the chemical formula C20H24N2O2
is a white crystalline powder that is very difficult to dissolve in water and has a bitter taste. The melting point of quinine is 177 degrees Celsius, while that of quinine trihydrate is 57 degrees Celsius. The molar mass of quinine is 324.44 grams x mol^-1. The lowest known toxic dose, i.e., the lowest dose that has been shown to be toxic in a human, after oral administration is 74 mg x kg^-1. The lowest proven lethal dose in humans is 294 mg x kg^-1, although the mode of administration in this case is unknown. Quinine is used both as a drug and as a bittering agent in foods. Quinine has long been a known drug for the treatment of malaria.
Pharmacological action
Normally, quinine is applied orally. However, intravenous application is also possible in emergencies. After oral administration, absorption of quinine is relatively rapid and good. The maximum effect is reached after 1-3 hours. Plasma protein binding of quinine is about 70%. Metabolization occurs almost completely in the liver, and only 10% of quinine is excreted unchanged. The effect of quinine is based on inhibition of hemopolymerase of plasmodia. Here, quinine prevents the formation of non-toxic β-hematin in the vacuoles of the plasmodia from toxic ferriprotophyrin IX. Plasmodia are the causative agents of malaria. Although several different plasmodia can be distinguished here. However, quinine is effective against all of the plasmodia species. Since the plasmodia require hemopolymerase, they are directly damaged by quinine. Furthermore, even in small doses, quinine has a local anesthetic and antipyretic effect. Quinine sulfate also has an antispasmodic effect. The antispasmodic effect of quinine sulfate is due to an action at the junction between nerves and muscle fibers of the motor end plate.
Medical application and use
Quinine is used primarily for the treatment of severe malaria tropica. Malaria tropica is the form of malaria caused by the pathogen Plasmodium falciparum. It is characterized by a relatively high concentration of the parasite in the blood (parasitemia). Malaria tropica often results in severe anemia and neurological complications. In addition, malaria tropica can result in a rhythmic course of fever. Malaria tropica also often leads to complications or changes in certain organs. Thus, kidney failure may also occur. Quinine is indicated for malaria tropica. Quinine is mainly used when the pathogens are resistant or multi-resistant to chloroquine. Quinine is administered in relatively high doses to treat malaria. The therapy is mostly administered orally in the form of salts of quinine. The amounts of the salts usually correspond to 0.8 to 1 g of quinine per day. Thus, for example, dosages of 1.95 grams of quinine sulfate dihydrate daily are used, which roughly correspond to the above-mentioned concentration of quinine. For all other indications of quinine, much lower dosages are used. Other indications are the prophylaxis and therapy of muscle cramps. The dosages administered here are around 200 to 400 milligrams of quinine sulfate per day. Outside of medicine, quinine is used in various foods due to its bitter taste. Especially the “bitter lemon” and the “tonic water” are well-known quinine-containing drinks.
Risks and side effects
In the context of an ingestion of quinine, quinine poisoning can occur in case of overdose. If this occurs, typical symptoms occur.They include dizziness, vomiting, ringing in the ears, visual disturbances, spasms of the retinal vessels, damage to the optic nerve, mostly temporary blindness, states of agitation, and cyanosis (bluish discoloration of the skin and mucous membranes). At worst, cardiac death from cardiac paralysis or death from central respiratory paralysis may occur. The lethal dose is about eight to ten grams. For the treatment of quinine poisoning, activated charcoal (or sodium sulfate) and benzodiazepines ( e.g., diazepam) are administered. The activated charcoal is to absorb the quinine and thus inhibit its absorption into the blood. The benzodiazepines serve to relax the muscles. Furthermore, other side effects may occur during therapy with quinine. Nausea, vomiting (emesis), diarrhea, abdominal pain, allergic symptoms, skin rash, asthma, thrombocytopenia, leukopenia, agranulocytosis, headache, dizziness, and confusion may occur. Furthermore, double vision, decreased visual acuity (and other visual disturbances), tinnitus, hearing loss (and other hearing disturbances), a drop in blood pressure, shock, and cardiac arrhythmias are possible adverse drug reactions that may be caused by quinine.
