====== Potassium-Sparing Diuretics ======

Potassium-sparing diuretics act at the collecting duct.

They reduce sodium reabsorption while preserving potassium.

These agents have weak diuretic effect but important clinical roles.

Used in:

  * [[cardio:heart_failure:start|Heart Failure]]
  * Resistant [[cardio:hypertension:start|Hypertension]]
  * Prevention of hypokalemia

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===== Site of Action =====

Collecting Duct

Normal physiology:

  * Aldosterone → ↑ ENaC expression
  * ↑ Sodium reabsorption
  * ↑ Potassium secretion

Potassium-sparing agents interfere with this process.

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===== Two Major Subclasses =====

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==== [[cardio:diuretics:potassium_sparing:mra|Mineralocorticoid Receptor Antagonists (MRAs)]] ====

Mechanism:

  * Block aldosterone receptor
  * ↓ ENaC expression
  * ↓ Sodium reabsorption
  * ↑ Potassium retention
  * ↓ Myocardial fibrosis

Agents:

  * [[cardio:hf:spironolactone|Spironolactone]]
  * [[cardio:hf:eplerenone|Eplerenone]]

Clinical Importance:

  * Mortality reduction in HFrEF
  * Preferred 4th-line agent in resistant hypertension
  * Treat primary hyperaldosteronism

Key Feature:

  * Neurohormonal blockade — not just diuresis

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==== [[cardio:diuretics:potassium_sparing:enac|ENaC Inhibitors]] ====

Mechanism:

  * Directly block epithelial sodium channel (ENaC)
  * Reduce sodium reabsorption
  * Reduce potassium secretion

Agents:

  * [[cardio:diuretics:amiloride|Amiloride]]
  * [[cardio:diuretics:triamterene|Triamterene]]

Clinical Use:

  * Prevent hypokalemia from:
      * [[cardio:diuretics:loop:start|Loop Diuretics]]
      * [[cardio:diuretics:thiazide:start|Thiazide Diuretics]]

No mortality benefit in heart failure.

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===== Electrolyte Effects =====

All potassium-sparing diuretics:

  * ↑ Potassium
  * Mild natriuresis

Risk:

  * Hyperkalemia
  * Worsened by:
      * [[cardio:raas:acei|ACE Inhibitors]]
      * [[cardio:raas:arb|ARBs]]
      * [[cardio:raas:direct_renin_inhibitor|Direct Renin Inhibitors]]

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===== MRAs vs ENaC Inhibitors =====

MRAs:

  * Block aldosterone receptor
  * Reduce cardiac remodeling
  * Reduce mortality in HFrEF
  * Cause endocrine side effects (spironolactone)

ENaC Inhibitors:

  * Pure potassium preservation
  * No cardiac remodeling benefit
  * Used primarily for electrolyte balance

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===== Clinical Pearls =====

  * Weak diuretics
  * Strong neurohormonal agents (MRAs)
  * Essential in HFrEF
  * Spironolactone causes gynecomastia
  * Monitor potassium closely
  * Hyperkalemia risk increases with RAAS blockade

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===== Related =====

  * [[cardio:diuretics:start|Diuretics]]
  * [[cardio:heart_failure:start|Heart Failure]]
  * [[cardio:hypertension:start|Hypertension]]
  * [[cardio:hf:spironolactone|Spironolactone]]
  * [[cardio:hf:eplerenone|Eplerenone]]