REVIEW Quinine is a naturally occurring quinuclidine alkaloid derived from the bark of the cinchona tree. It is used as an antimalarial drug, and is the active ingredient in extracts of the cinchona that have been used for that purpose since before 1633. The medicinal properties of the cinchona tree were originally discovered by the Quechua, who are indigenous to Peru and Bolivia; later, the Jesuits were the first to bring cinchona to Europe. Quinine is also a mild antipyretic and analgesic and has been used in common cold preparations for that purpose. It was used commonly as a bitter and flavoring agent, and is still useful for the treatment of babesiosis. Quinine is also useful in some muscular disorders, especially nocturnal leg cramps and myotonia congenita, because of its direct effects on muscle membrane and sodium channels
Quinine was the first effective treatment for malaria caused by Plasmodium falciparum, appearing in therapeutics in the 17th century. It remained the antimalarial drug of choice until the 1940s, when other drugs such as chloroquine that have fewer unpleasant side effects replaced it. Since then, many effective antimalarials have been introduced, although quinine is still used to treat the disease in certain critical circumstances, such as severe malaria, and in impoverished regions due to its low cost. The mechanisms of its antimalarial effects are not well understood. The most widely accepted hypothesis of its action is based on the well-studied and closely related quinoline drug, chloroquine. This model involves the inhibition of hemozoin biocrystallization, which facilitates the aggregation of cytotoxic heme. Free cytotoxic heme accumulates in the parasites, causing their deaths.
Quinine is available with a prescription in the United States and over-the-counter, in minute quantities, in tonic water. Quinine is also used to treat lupus and arthritis. Quinine was also frequently prescribed in the US as an off-label treatment for nocturnal leg cramps, but this has become less prevalent due to a Food and Drug Administration statement warning against the practice.
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