Quinidine
Substance obtained from cinchona bark that was formerly used as an antiarrhythmic and is now hardly used because of its side effects. It can prolong the QT interval and trigger dangerous arrhythmias.
See also: Antiarrhythmic drugs
Quinine
Substance from cinchona bark that was long the most important antimalarial and is now used only as a reserve in severe cases. Because of possible heart rhythm, blood and visual disturbances, it is used only very cautiously for leg cramps.
See also: Quinidine