- Originally, any one of hundreds of plant and fungal products distinguished by alkaline (basic) reactions, but now restricted to heterocyclic nitrogen-containing and often complex structures possessing pharmacologic activity; their trivial name s usually end in -ine ( e.g., morphine, atropine, colchicine). Alkaloids are synthesized by plants and are found in the leaf, bark, seed, or other parts, usually constituting the active principle of the crude drug; they are a loosely defined group, but may be classified according to the chemical structure of their main nucleus. For medicinal purposes, due to improved water solubility, the salts of alkaloids ( e.g., morphine sulfate, codeine phosphate) are usually used. see also individual a. or a. class. SYN: vegetable base.- ergot alkaloids (er′got) any of a large number of alkaloids obtained from the ergot fungus Claviceps purpurea or semisynthetically derived; examples include ergotamine, ergonovine, dihydroergotamine, lysergic acid diethylamide (LSD), methysergide.- fixed a. a nonvolatile a..- Vinca alkaloids alkaloids such as vincristine and vinblastine (antitumor agents) extracted from the periwinkle plant. SYN: Catharanthus alkaloids.
* * *al·ka·loid 'al-kə-.lȯid n any of numerous usu. colorless, complex, and bitter organic bases (as morphine or caffeine) containing nitrogen and usu. oxygen that occur esp. in seed plants and are typically physiologically activeal·ka·loi·dal .al-kə-'lȯid-əl adj
* * *n.one of a diverse group of nitrogen-containing substances that are produced by plants and have potent effects on body function. Many alkaloids are important drugs, including morphine, quinine, atropine, and codeine.
* * *al·ka·loid (alґkə-loid″) [alkali + -oid] one of a large group of nitrogenous basic substances found in plants. They are usually very bitter and many are pharmacologically active. Examples are atropine, caffeine, coniine, morphine, nicotine, quinine, and strychnine. The term is also applied to synthetic substances (artificial a's) which have structures similar to plant alkaloids, such as procaine.
Medical dictionary. 2011.