Potassium sparing diuretics inhibit the reabsorption of sodium (and water) from the distal tubule by antagonising aldosterone. They have only a relatively weak diuretic effect. They reduce potassium excretion (hence the name “potassium sparing”).
- Aldosterone causes the synthesis of more sodium channels. Spironolactone and eplerenone competitively bind to the receptors that cause this action.
- Amiloride and triamterene have a different mechanism of action, and they directly block the sodium channels at the luminal surface of the renal tubule – and hence reduce the reabsorption of sodium.
Aldosterone is thought to contribute to the pathophysiology of heart failure, and as such, potassium sparing diuretics are frequently used to treat heart failure. In fact, they are one of the only medical treatments for heart filature that improve long term outcome.
Spironolactone is the most commonly used potassium sparing diuretic.
The kidney is complicated, you might want to read about renal physiology to help understand how diuretics work.
- Hyperkalaemia is more common in those with pre-existing renal disease or who are also taking ACE-inhibitors. Magnesium retention occurs, in contrast to the other diuretics. It also occurs in pre-existing renal disease, and their use should be avoided in severe renal impairment (see below).
- Spironolactone is able to bind to oestrogen receptors. This can cause gynecomastia and impotence in men, and menstrual problems in women. Eplerenone has greater steroid receptor specificity and does not cause these problems.
Uses and indications
- Heart failure
- Causes of hyperaldosteronism (potassium sparing diuretics help to reduce oedema in these circumstances)
- Liver Failure
- Resistant hypertension
Contraindications and Cautions
- Contraindicated Renal failure – typically contra-indicated if Creatinine clearance <30
- Increases risk of hyperkalaemia
- Can cause feminisation of the male fetus
- Breastfeeding – safe to use
- Australian Medicines Handbook – Spironolactone
- Waller, DG., Renwick AG., Hillier K. (2005). Medical Pharmacology and Therapeutics. 2nd ed. Elsevier Saunders