Potassium-sparing diuretics have weaker diuretic and antihyper- tensive effects than other diuretics but provide the advantage of conserving potassium. These drugs include amiloride, spironolac- tone, and triamterene.
Potassium-sparing diuretics are only available orally and are ab- sorbed in the GI tract. They’re metabolized by the liver (except for amiloride, which isn’t metabolized) and excreted primarily in urine.
The direct action of potassium-sparing diuretics on the distal tubule of the kidneys results in urinary excretion of sodium, water, bicarbonate, and calcium. The drug also decreases the excretion of potassium and hydrogen ions. These effects lead to reduced blood pressure and increased serum potassium levels.
Structurally similar to aldosterone, spironolactone acts as an aldosterone antagonist. Aldosterone promotes the retention of sodium and water and the loss of potassium, whereas spironolactone counteracts these effects by competing with aldosterone for receptor sites. As a result, sodium, chloride, and water are excreted and potassium is retained.
Potassium-sparing diuretics are used to treat:
• diuretic-induced hypokalemia in patients with heart failure
• nephrotic syndrome (abnormal condition of the kidneys)
• heart failure
Spironolactone also is used to treat hyperaldosteronism (exces-sive secretion of aldosterone) and hirsutism (excessive hair growth), including hirsutism associated with Stein-Leventhal (polycystic ovary) syndrome. Potassium-sparing diuretics are commonly used with other diuretics to potentiate their action or counteract their potassium-wasting effects.
Giving potassium-sparing diuretics with potassium supplements or angiotensin-converting enzyme inhibitors increases the risk of hyperkalemia. Concurrent use of spironolactone and digoxin in-creases the risk of digoxin toxicity. (See Adverse reactions topotassium-sparing diuretics.)