Loop diuretics exert their diuretic effect by inhibiting reabsorption from the ascending loop of Henle, and thus are powerful diuretics. They have a tendency to cause hypokalaemia. They have less effect on bicarbonate than the thiazides.
Loop diuretics cause a dose-related diuresis within one hour of oral administration. The effect diminishes after six hours. When given intravenously, they also cause venodilatation.