Diuretics are drugs that increase urine output by acting on the kidneys, commonly used in treating hypertension, heart failure, liver cirrhosis, and kidney disorders. Most diuretics (like loop and thiazides) lead to potassium loss, which can result in hypokalemia (low potassium levels).
However, a special group known as Potassium-Sparing Diuretics (PSDs) prevent excessive potassium excretion. These drugs act primarily on the distal nephron (late distal tubules and collecting ducts) and are often used in combination with other diuretics to balance potassium levels.
To simplify their classification and recall, medical students often use the mnemonic PASTE.
Mnemonic PASTE for Potassium-Sparing Diuretics
The mnemonic PASTE helps remember the major potassium-sparing diuretics:
| Letter | Drug | Details |
|---|---|---|
| P | Potassium-Sparing Diuretics | Group name |
| A | Amiloride | Blocks epithelial sodium channels (ENaCs) in the collecting ducts. |
| S | Spironolactone | Aldosterone antagonist, prevents sodium reabsorption and potassium loss. |
| T | Triamterene | Similar to amiloride, ENaC blocker. |
| E | Eplerenone | Selective aldosterone antagonist, fewer side effects compared to spironolactone. |
A visual association with toothpaste (as shown in the diagram) makes it easier to recall: “Potassium-sparing diuretics = PASTE like toothpaste.”
Classification of Potassium-Sparing Diuretics
Potassium-sparing diuretics can be divided into two groups based on their mechanism:
1. Aldosterone Antagonists (Mineralocorticoid Receptor Antagonists)
- Spironolactone
- Eplerenone
2. Epithelial Sodium Channel (ENaC) Blockers
- Amiloride
- Triamterene
Mechanism of Action
1. Aldosterone Antagonists (Spironolactone, Eplerenone):
- Block aldosterone receptors in the distal nephron.
- Decrease sodium reabsorption and potassium secretion.
- Result: Natriuresis with potassium retention.
- Directly block sodium channels in the collecting ducts.
- Reduce sodium reabsorption, decrease potassium excretion.
- Result: Mild diuresis with potassium retention.
Clinical Uses of Potassium-Sparing Diuretics
Potassium-sparing diuretics are not strong diuretics by themselves but are valuable in specific conditions:
1. Hypertension
Used in combination with thiazides or loop diuretics to prevent hypokalemia.2. Heart Failure
Spironolactone and eplerenone improve survival in chronic heart failure by reducing aldosterone-mediated myocardial fibrosis and remodeling.3. Primary Hyperaldosteronism (Conn’s Syndrome)
Spironolactone is the drug of choice.4. Secondary Hyperaldosteronism
Seen in cirrhosis, nephrotic syndrome, and congestive heart failure.5. Hypokalemia
Used to prevent or treat diuretic-induced hypokalemia.6. Polycystic Ovary Syndrome (PCOS)
Spironolactone helps reduce androgen levels and hirsutism.7. Lithium-Induced Nephrogenic Diabetes Insipidus
Amiloride reduces lithium entry into collecting duct cells, preventing toxicity.Side Effects of Potassium-Sparing Diuretics
While beneficial, these drugs can cause side effects:
1. Hyperkalemia – Most significant risk, especially in renal failure or when combined with ACE inhibitors/ARBs.3. Spironolactone-Specific Side Effects:
- Gynecomastia
- Impotence
- Menstrual irregularities
- Breast tenderness
Contraindications
- Severe renal impairment (risk of hyperkalemia).
- Hyperkalemia or predisposition to it.
- Concurrent potassium supplements or ACE inhibitors/ARBs (unless carefully monitored).
- Pregnancy: Spironolactone is not recommended due to antiandrogenic effects.
Comparison Table of Potassium-Sparing Diuretics
| Drug | Class | Mechanism | Special Use | Side Effects |
|---|---|---|---|---|
| Spironolactone | Aldosterone antagonist | Blocks mineralocorticoid receptor | Hyperaldosteronism, heart failure, PCOS | Gynecomastia, menstrual irregularities |
| Eplerenone | Aldosterone antagonist | Selective receptor blocker | Heart failure, post-MI | Less hormonal side effects |
| Amiloride | ENaC blocker | Blocks sodium channels | Lithium-induced diabetes insipidus | Hyperkalemia |
| Triamterene | ENaC blocker | Blocks sodium channels | Combination with thiazides | Kidney stones, hyperkalemia |
Frequently Asked Questions (FAQ)
Q1. What is the mnemonic to remember potassium-sparing diuretics?
The mnemonic PASTE stands for Potassium-sparing diuretics, Amiloride, Spironolactone, Triamterene, and Eplerenone.
Q2. Why are potassium-sparing diuretics called “potassium-sparing”?
Because they reduce sodium reabsorption in the kidney while preventing potassium excretion, thus “sparing” potassium.
Q3. Can potassium-sparing diuretics be used alone for hypertension?
They are usually not used as first-line agents due to weak diuretic action but are effective in combination therapy with thiazides or loop diuretics.
Q4. Which potassium-sparing diuretic is safest for patients with gynecomastia risk?
Eplerenone – it has minimal antiandrogenic side effects compared to spironolactone.
Q5. How do potassium-sparing diuretics benefit patients with heart failure?
They block aldosterone, reducing cardiac remodeling and fibrosis, thereby improving survival.
Q6. What is the major risk of potassium-sparing diuretics?
Hyperkalemia, which can lead to life-threatening cardiac arrhythmias if not monitored.
