💊 Potassium-Sparing Diuretics

Potassium-sparing diuretics are a class of diuretics that increase diuresis without causing significant potassium loss. They are often used in combination with other diuretics to counteract potassium wasting.

This class includes two main types: aldosterone antagonists (e.g., spironolactone, eplerenone) and epithelial sodium channel (ENaC) inhibitors (e.g., amiloride, triamterene). Aldosterone antagonists block aldosterone receptors, preventing sodium reabsorption and potassium excretion in the collecting duct. ENaC inhibitors directly block sodium channels in the collecting duct, reducing sodium reabsorption and thus potassium excretion.

Potassium-sparing diuretics are indicated for the treatment of oedema and ascites associated with heart failure and liver cirrhosis, often in combination with loop diuretics. Aldosterone antagonists are particularly important in chronic heart failure with reduced ejection fraction. They are also used for hypertension, especially when hypokalaemia is a concern or in primary hyperaldosteronism (Conn's syndrome).

Absolute contraindications include hyperkalaemia, severe renal impairment, and Addison's disease. They should be used with caution in patients with diabetes or in combination with other drugs that increase potassium levels, due to the significant risk of life-threatening hyperkalaemia.

The most significant adverse effect is hyperkalaemia, which can be life-threatening. Other common effects include hyponatraemia, gastrointestinal disturbances, and dizziness. Spironolactone can cause anti-androgenic effects such as gynaecomastia, impotence, and menstrual irregularities, which are less common with eplerenone.

Frequent monitoring of serum potassium and renal function (urea, creatinine) is crucial, especially during initiation and dose changes. Blood pressure should also be monitored. In patients on spironolactone, watch for signs of gynaecomastia.

When prescribing, always check recent potassium and renal function results. Counsel patients on the importance of regular blood tests and to report symptoms of muscle weakness or palpitations. Avoid concomitant use with potassium supplements or other potassium-raising drugs (e.g., ACE inhibitors) unless closely monitored.

High-yield facts include their role in preventing hypokalaemia when combined with loop or thiazide diuretics, and their specific indications in heart failure and liver cirrhosis. Remember the significant risk of hyperkalaemia and the anti-androgenic effects of spironolactone. Spironolactone and eplerenone are aldosterone antagonists, while amiloride and triamterene are ENaC inhibitors.

SBAs frequently test the understanding of hyperkalaemia as the primary adverse effect and the rationale for combining them with other diuretics. Questions might present a patient with heart failure and ask about the role of spironolactone, or a patient developing hyperkalaemia on a diuretic regimen. Distinguishing between spironolactone and eplerenone's side effect profiles is also a common theme.