9.2C Potassium-Sparing Diuretics

Potassium-Sparing Diuretics mechanism of action

Potassium-sparing diuretics act in the collecting ducts of the nephron, where they block the action of aldosterone, a hormone responsible for promoting sodium reabsorption and potassium excretion.

By antagonising aldosterone at the mineralocorticoid receptors, potassium-sparing diuretics reduce sodium reabsorption

and promote sodium and water excretion while preventing the loss of potassium.

Aldosterone increases the number of sodium channels in the distal nephron, and potassium-sparing diuretics prevent this,

which leads to sodium excretion without the associated potassium loss seen with other diuretics.

Potassium-Sparing Diuretics rationale for use

• often used in combination with other diuretics, particularly loop or thiazide diuretics, to prevent potassium depletion.

They are particularly useful in conditions where aldosterone plays a significant role, such as

heart failure,

primary hyperaldosteronism,

and liver cirrhosis (where aldosterone levels are elevated).

Potassium-Sparing Diuretics example

• Spironolactone.

• Eplerenone.

Potassium-Sparing Diuretics dose regimen

• Spironolactone: Eplerenone:

• Spironolactone:

Typically prescribed at 25–400 mg daily, depending on the severity of oedema and the underlying condition.

• Eplerenone:

Usually started at a dose of 25 mg once daily, particularly in heart failure patients, with doses adjusted based on potassium levels and renal function.

Potassium-Sparing Diuretics monitoring

• Potassium levels must be monitored regularly, as potassium-sparing diuretics can cause hyperkalaemia, which can be life-threatening.

• Renal function (creatinine and eGFR) should also be monitored, especially in patients with pre-existing kidney disease.

Potassium-Sparing Diuretics side effects

• Hyperkalaemia:

• Gynaecomastia:

• Menstrual irregularities:

Hyperkalaemia:

Elevated potassium levels can lead to dangerous arrhythmias, which may be fatal if not managed.

Gynaecomastia:

A side effect specific to spironolactone, this is due to its anti-androgenic effects, as it also antagonises androgen receptors.

Menstrual irregularities:

Spironolactone can cause irregular periods and breast tenderness in women.

Potassium-Sparing Diuretics patient counselling

• Avoid potassium-rich foods: Advise patients to avoid foods high in potassium, such as bananas, oranges, and potatoes, as these can exacerbate      the risk of hyperkalaemia.

• Regular blood tests: Emphasise the importance of regular monitoring of potassium levels and renal function to avoid complications.

• Report symptoms: Encourage patients to report symptoms such as muscle weakness, palpitations, or chest pain, which may indicate dangerously high potassium levels.