It can also cause serious hypersensitivity reactions including anaphylactic shock, urticaria, serious skin rashes, including Stevens–Johnson syndrome and toxic epidermal necrolysis, angioedema, facial edema, bronchospasm, granulomatous hepatitis, and itchiness.The most common adverse effects involve a group of symptoms called cinchonism, which can include headache, vasodilation and sweating, nausea, tinnitus, hearing impairment, vertigo or dizziness, blurred vision, and disturbance in color perception. More severe cinchonism includes vomiting, diarrhea, abdominal pain, deafness, blindness, and disturbances in heart rhythms. Cinchonism is much less common when quinine is given by mouth, but oral quinine is not well tolerated (quinine is exceedingly bitter and many people will vomit after ingesting quinine tablets). Other drugs, such as Fansidar (sulfadoxine with pyrimethamine) or Malarone (proguanil with atovaquone), are often used when oral therapy is required. Quinine ethyl carbonate is tasteless and odourless, but is available commercially only in Japan. Blood glucose, electrolyte and cardiac monitoring are not necessary when quinine is given by mouth. Quinine has diverse unwanted interactions with numerous prescription drugs, such as potentiating the anticoagulant effects of warfarin. Mechanism of action
Quinine is used for its toxicity to the malarial pathogen, Plasmodium falciparum, by interfering with its ability to dissolve and metabolize hemoglobin. As with other quinoline antimalarial drugs, the precise mechanism of action of quinine has not been fully resolved, although in vitro studies indicate it inhibits nucleic acid and protein synthesis, and inhibits glycolysis in P. falciparum. The most widely accepted hypothesis of its action is based on the well-studied and closely related quinoline drug, chloroquine.
The new quinoline heterocycle would then be formed by combining this amine with the aldehyde produced in the tryptamine side-chain cleavage, giving cinchonidinone. For the last step, hydroxylation and methylation gives quinine. Catalysis
Quinine and other Cinchona alkaloids can be used as catalysts for stereoselective reactions in organic synthesis. : Table 3B Plate 560  For example, the quinine-catalyzed Michael addition of a malononitrile to α,β-enones gives a high degree of sterechemical control. History
Quinine was used as a muscle relaxant by the Quechua people, who are indigenous to Peru, Bolivia and Ecuador, to halt shivering. The Quechua would mix the ground bark of cinchona trees with sweetened water to offset the barks bitter taste, thus producing something similar to tonic water.Spanish Jesuit missionaries were the first to bring cinchona to Europe. The Spanish had observed the Quechuas use of cinchona and were aware of the medicinal properties of cinchona bark by the 1570s or earlier:  Nicolás Monardes (1571) and Juan Fragoso (1572) both described a tree, which was subsequently identified as the cinchona tree, whose bark was used to produce a drink to treat diarrhea. Quinine has been used in unextracted form by Europeans since at least the early 17th century.A popular story of how it was brought to Europe by the Countess of Chinchon was debunked by medical historian Alec Haggis around 1941. During the 17th century, malaria was endemic to the swamps and marshes surrounding the city of Rome. It had caused the deaths of several popes, many cardinals and countless common Roman citizens.