Cinchona trees remain the only practical source of quinine. However, under wartime pressure, research towards its artificial production was undertaken. A formal chemical synthesis was accomplished in 1944 by American chemists R.B. Woodward and W.E. Doering. Since then, several more efficient quinine total syntheses have been achieved , but none of them can compete in economic terms with isolation of the alkaloid from natural sources.
Dosing
Quinine is a basic amine and is therefore always presented as a salt. Various preparations that exist include the hydrochloride, dihydrochloride, sulfate, bisulfate and gluconate. This makes quinine dosing very complicated, because each of the salts has a different weight.
The following amounts of each form are equal :
- quinine base 100 mg
- quinine bisulfate 169 mg
- quinine dihydrochloride 122 mg
- quinine hydrochloride 122 mg
- quinine sulfate 121 mg
- quinine gluconate 160 mg.
All quinine salts may be given orally or intravenously quinine gluconate may also be given intramuscularly (IM) or rectally (PR).The main problem with the rectal route is that the dose can be expelled before it is completely absorbed, but this can be rectified by giving half dose again.
Side effects
It is usual for quinine in therapeutic doses to cause cinchonism; in rare cases, it may even cause death (usually by pulmonary edema). The development of mild cinchonism is not a reason for stopping or interrupting quinine therapy and the patient should be reassured. Blood glucose levels and electrolyte concentrations must be monitored when quinine is given by injection; the patient should also ideally be in cardiac monitoring when the first quinine injection is given (these precautions are often unavailable in developing countries where malaria is most a problem).
Cinchonism is much less common when quinine is given by mouth, but oral quinine is not well tolerated (quinine is exceedingly bitter and many patients will vomit up quinine tablets): other drugs such as Fansidar® (sulfadoxine (sulfonamide antibiotic) with pyrimethamine) or Malarone® (proguanil with atovaquone) are often used when oral therapy is required. Blood glucose, electrolyte and cardiac monitoring are not necessary when quinine is given by mouth.
Non-medical uses of quinine
Quinine is a flavour component of tonic water, bitter lemon, and vermouth. According to tradition, the bitter taste of anti-malarial quinine tonic led British colonials in India to mix it with gin, thus creating the gin and tonic cocktail, which is still popular today in many parts of the world.
In the United States, the Food and Drug Administration limits tonic water quinine to 83 parts per million, which is one-half to one-quarter the concentration used in therapeutic tonic.
Because of its relatively constant and well-known fluorescence quantum yield, quinine is also used in photochemistry as a common fluorescence standard. In the United States, quinine is an ingredient in the Howling monkey energy drink. In Canada, quinine is an ingredient in the carbonated chinotto beverage called Brio. In the United Kingdom, quinine is an ingredient in the carbonated and caffeinated beverage, Irn-Bru.
