Quinine and its naturally occurring stereoisomer quinidine are natural alkaloids found in the bark of the cinchona tree, originally from South America. Today, quinine and quinidine are individually synthesized for pharmaceutical and medical purposes. Both are effective antimalarial drugs; however, quinidine is also prescribed as a class 1a antiarrhythmic medication. Quinine and quinidine both have a similar mechanism of action as antimalarial drugs. They interfere with the malaria parasite’s ability to digest hemoglobin, with quinidine being reportedly more effective in doing so. Quinine and quinidine also block sodium and potassium channels to stabilize heart rhythm, but only quinidine is prescribed for this purpose. The drugs are mainly metabolized via CYP2D6 to an inactive 3-hydroxyquinine and 3-hydroxyquinidine metabolite, respectively. Trade names for quinine include, Qualaquin® and for quinidine include Cardioquin®, Cin-Quin®, and Quinidex®. Quinine is also present in some food and beverages such as teas, Bitter Lemon, and Tonic Water. Laboratory tests may not distinguish between quinine and quinidine, and their presence may be reported non-specifically as undifferentiated quinine/quinidine.
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