Pharmacology of Potassium-Sparing Diuretics

Mechanism of Action:

Potassium-sparing diuretics act on the collecting ducts in the kidneys. They inhibit sodium reabsorption while reducing potassium secretion, effectively sparing potassium levels in the body.

There are two main types:

1. Aldosterone Antagonists: Block the action of aldosterone, a hormone that promotes sodium reabsorption and potassium excretion.
2. Sodium Channel Blockers (epithelial): Directly inhibit sodium channels in the collecting ducts.

Pharmacokinetics:

• Absorption: Variable oral absorption.
• Distribution: Limited distribution; some are protein-bound.
• Metabolism: Liver metabolism for some agents like spironolactone.
• Excretion: Primarily renal excretion.

Drug Examples:

• Spironolactone (Aldactone): Aldosterone antagonist; also has anti-androgenic effects.
• Eplerenone (Inspra): Selective aldosterone antagonist.
• Amiloride: Sodium channel blocker.
• Triamterene: Sodium channel blocker.

Clinical Use:

1. Hypokalemia: To prevent or treat low potassium levels.
2. Heart Failure: Often used in combination with other diuretics.
3. Ascites: In liver disease to prevent hypokalemia.
4. Hyperaldosteronism: To counteract the effects of high aldosterone levels.

Side Effects:

• Hyperkalemia: High potassium levels
• Gynecomastia: With spironolactone use
• Renal impairment: Risk of acute kidney injury
• Acid-base imbalances

Drug Interactions:

• ACE Inhibitors: Increased risk of hyperkalemia.
• Potassium Supplements: Increased risk of hyperkalemia.
• NSAIDs: Reduced diuretic effect.

Contraindications:

• Severe renal impairment.
• Hyperkalemia.
• Known hypersensitivity to the drug.

Understanding the pharmacology of potassium-sparing diuretics is essential for healthcare providers to effectively treat conditions like hypokalemia and heart failure while minimizing side effects.