Spironolactone (potassium sparing diuretic) and Furosemide (loop diuretic) have different but complementary mechanisms and sites of action. Therefore, when given together they produce additive or synergistic diuretic. The Furosemide component inhibits the Na+/K+/2Cl- co-transporter in the ascending Loop of Henle and blocks the reabsorption of sodium, potassium and chloride ions; thereby increasing the quantity of sodium and the volume of water excreted in the urine. This characteristically induces potassium loss. The spironolactone component inhibits the reabsorption of sodium in exchange for potassium at the distal tubule by antagonising the action of aldosterone so that sodium excretion is greatly favoured and the excess loss of potassium, induced by the Furosemide, is reduced