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.

Vincaleukoblastine and vincristine, two alkaloids derived from the periwinkle plant (Catharanthus roseus), are used effectively for the treatment of white-blood-cell cancers. Vincaleukoblastine is especially useful against lymphoma (cancer of the lymph glands), while vincristine is used against the most common form of childhood leukemia.

Atropine is an alkaloid produced by several plants, including deadly nightshade (Atropa belladonna), Jimson weed (Datura stramonium), and henbane (Hyoscyamus niger). It has a variety of medical uses, as it is able to relax smooth muscle by blocking action of the neurotransmitter acetylcholine. Atropine is most commonly used to dilate the pupil during eye examinations. Atropine also relieves nasal congestion and serves as an antidote to nerve gas and insecticide poisoning.

Pilocarpine, derived from several Brazilian shrubs of the genus Pilocarpus, is another alkaloid used in ophthalmology, the medical specialty that treats the eye. This drug stimulates the drainage of excess fluid from the eyeball, relieving the high pressure in the eye caused by glaucoma. If untreated, glaucoma can lead to blindness.

Introduction of reserpine in the 1950s revolutionized high blood pressure treatment and brought new hope to those suffering from this previously untreatable and life-threatening condition. Derived from tropical trees and shrubs of the genus Aauwolfia, reserpine works by depleting the body's stores of the neurotransmitter norepinephrine. Among its other functions, norepinephrine contracts the arteries and thereby contributes to high blood pressure.

Unfortunately, reserpine also causes drowsiness and sometimes severe depression. Medications without these side effects have been developed in recent decades, and reserpine is rarely used.