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Alkaloid
A number of alkaloids are used as drugs. Among the oldest and best known of these is quinine, derived from the bark of the tropical cinchona tree. Indians of South America have long used cinchona bark to reduce fever, much as willow bark was used in Europe as a source of aspirin. In the 1600s Europeans discovered that the bark could actually cure malaria—one of the most debilitating and fatal diseases of tropical and subtropical regions.
Quinine was purified as early as 1823, and soon it replaced crude cinchona bark as the standard treatment for malaria. Not until the 1930s was quinine replaced by synthetic analogues that offered fewer side effects and a more reliable supply. Quinine is still used as the principal flavoring agent in tonic water—a beverage named for its ability to prevent malarial symptoms.
Cinchona bark also produces quinidine. It is used primarily to control abnormalities of heart rhythm such as fibrillation, a series of rapidly quivering beats that do not pump any blood, and heart block, a condition in which electrical currents fail to coordinate the contractions of the upper and lower chambers of the heart.
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