Anesthesia: Potassium Sparing Diuretics

POTASSIUM SPARING DIURETICS

      These are weak diuretic agents and characteristically do not increase potassium excretion. Potassium-sparing diuretics inhibit Na+ reabsorption in the col-lecting tubules and therefore can maximally excrete only 1–2% of the filtered Na+ load. They are usually used in conjunction with more potent diuretics for their potassium-sparing effect.

1.Aldosterone Antagonists (Spironolactone & Eplerenone)

Spironolactone (Aldactone) and eplerenone are direct aldosterone receptor antagonists in collecting tubules. They inhibit aldosterone-mediated Na⁺ reabsorption and K⁺ secretion. Both agents have been shown to improve survival in patients with chronic heart fail-ure. Aldosterone may produce gynecomastia in male patients due to its antiandrogenic properties.

Uses

These agents may be used as adjuvants in the treat-ment of refractory edematous states associated with secondary hyperaldosteronism . Spironolactone is particularly effective in patients with ascites related to advanced liver disease. They have become part of the standard medical manage-ment of chronic heart failure.

Intravenous Dosage

Th ese agents are only given orally.

Side Effects

These agents can result in hyperkalemia in patients with high potassium intake or renal insufficiency and in those receiving β blockers or ACE inhibitors. Metabolic acidosis may also be seen. Eplerenone lacks spironolactone’s side effects of gynecomastia and sexual dysfunction.

2. Noncompetitive Potassium-Sparing Diuretics

Triamterene (Dyrenium) and amiloride (Midamor) are not dependent on aldosterone activity in the collecting tubule. They inhibit Na⁺ reabsorption and K⁺ secretion by decreasing the number of open sodium channels in the luminal membrane of col-lecting tubules. Amiloride may also inhibit Na⁺–K⁺-ATPase activity in the collecting tubule.

Uses

In patients with hypertension, these agents are often combined with a thiazide or similar diuretic to minimize hypokalemia produced by the other agent. They have been added to more potent loop diuretics in congestive heart failure patients with marked potassium wasting.

Intravenous Dosages

Th ese agents are only given orally.

Side Effects

Amiloride and triamterene can cause hyperkalemia and metabolic acidosis similar to that seen with spi-ronolactone (see above). Both can also cause nau-sea, vomiting, and diarrhea. Amiloride is generally associated with fewer side effects, but paresthesias, depression, muscle weakness, and cramping may occasionally be seen. Triamterene on rare occasions has resulted in renal stones and is potentially neph-rotoxic, particularly when combined with nonste-roidal antiinflammatory agents.