Potassium Sparing Diutetic

Question 1

Example of a Potassium Sparing Diuretic

Answer 1

Spironolactone

Question 2

How do Potassium Sparing Diuretics work?

Answer 2

Aldosterone is a mineralocorticoid that is produced in the adrenal cortex. It acts on mineralocorticoid receptors in the distal tubules of the kidney to increase the activity of luminal epithelial sodium channels (ENaC). This increases the reabsorption of sodium and water (which elevates blood pressure) with the by-product of increased potassium excretion.

Aldosterone antagonists inhibit the effect of aldosterone by competitively binding to the aldosterone receptor. This increases sodium and water excretion and potassium retention. Their effect is greatest in primary hyperaldosteronism or when circulating aldosterone is increased, e.g. in cirrhosis.

Question 3

Indications of Potassium Sparing Diuretics

Answer 3

Ascites and oedema due to liver cirrhosis: spironolactone is the first-line diuretic.

Chronic heart failure: of at least moderate severity or arising within 1 month of a myocardial infarction, usually as an addition to a β-blocker and an ACE inhibitor/angiotensin receptor blocker.

Question 4

Contra-indications of Potassium Sparing Diuretics

Answer 4

Aldosterone antagonists are contraindicated in patients with severe renal impairment, hyperkalaemia and Addison’s disease (who are aldosterone deficient). Aldosterone antagonists can cross the placenta during pregnancy and appear in breast milk so should be avoided where possible in pregnant or lactating women.

Question 5

Side-effects of Potassium Sparing Diuretics

Answer 5

Hyperkalaemia: which can lead to muscle weakness, arrhythmias and even cardiac arrest.
Spironolactone causes gynaecomastia, which can have a significant impact on patient adherence.
Aldosterone antagonists can cause liver impairment and jaundice and are a cause of Stevens–Johnson syndrome (a T cell-mediated hypersensitivity reaction) that causes a bullous skin eruption.

Question 6

Possible interactions of Potassium Sparing Diuretics

Answer 6

The combination of an aldosterone antagonist with other potassium-elevating drugs, including ACE inhibitors and angiotensin receptor blockers, increases the risk of hyperkalaemia. Nevertheless, when supported by appropriate monitoring, this may be a beneficial combination in the context of heart failure. Aldosterone antagonists should not be combined with potassium supplements except in specialist practice

Question 7

Elimination of Potassium Sparing Diuretics

Answer 7

Renal

Question 8

Patient information of Potassium Sparing Diuretics

Answer 8

Aldosterone antagonists are only available as oral preparations.

Spironolactone should generally be taken with food.

Advise all patients that aldosterone antagonists can cause their potassium level to rise and reinforce the importance of attending for blood tests.

Spironolactone is a relatively weak diuretic that takes several days to start having an effect. It is therefore usually prescribed in combination with a loop or thiazide diuretic, where it both counteracts potassium wasting and potentiates the diuretic effect. For example, in the treatment of ascites due to chronic liver failure, spironolactone and furosemide are generally used together in a ratio of about 5 : 1 (e.g. spironolactone 200 mg with furosemide 40 mg).