Furosemide (FSM)

Furosemide is a loop diuretic used in the treatment of congestive heart failure and edema. Furosemide, like other loop diuretics, acts by inhibiting NKCC2, the luminal Na-K-2Cl symporter in the thick ascending limb of the loop of Henle. The action on the distal tubules is independent of any inhibitory effect on carbonic anhydrase or aldosterone; it also abolishes the corticomedullary osmotic gradient and blocks negative, as well as positive, free water clearance. Because of the large NaCl absorptive capacity of the loop of Henle, diuresis is not limited by development of acidosis, as it is with the carbonic anhydrase inhibitors. By inhibiting the transporter, the loop diuretics reduce the reabsorption of NaCl and also diminish the lumen-positive potential that derives from K+ recycling. This electrical potential normally drives divalent cation reabsorption in the loop, and by reducing this potential, loop diuretics cause an increase in Mg2+ and Ca2+ excretion.