Pharmacology · Potassium-sparing diuretics
Spironolactone !
An aldosterone blocker: a potassium-sparing diuretic that lowers mortality in heart failure and treats ascites and hyperaldosteronism.
Updated 2026-11-01
The figure shows spironolactone in the ligand-binding domain of the human mineralocorticoid receptor.
Mechanism of action
Spironolactone and its active metabolites (such as canrenone) compete with aldosterone for the mineralocorticoid receptor in the collecting duct. Without aldosterone's signal the cell makes fewer ENaC channels and Na⁺/K⁺ pumps, so less sodium is reabsorbed and less potassium and hydrogen are secreted. In the heart and vessels it reduces aldosterone-driven fibrosis. It also blocks androgen receptors, which explains gynecomastia.
- Spironolactone occupies the aldosterone receptor
- Fewer ENaC channels and Na⁺/K⁺ pumps in the collecting duct
- Na⁺ is lost in the urine; K⁺ and H⁺ are retained
- Less aldosterone-driven fibrosis in the heart
Pharmacokinetics
- Absorption
- Absorbed by mouth; food increases absorption
- Distribution
- Over 90% bound to plasma proteins
- Metabolism
- Rapid and extensive in the liver, to active metabolites such as canrenone
- Elimination
- Metabolites in urine and, secondarily, bile
- Half-life
- Parent drug about 1.4 hours; active metabolites about 14 to 17 hours
- Onset and duration
- The diuretic effect builds over several days
Indications
- Heart failure with reduced ejection fraction, to improve survival Heart failure →
- Resistant hypertension, as add-on therapy Arterial hypertension →
- Oedema and ascites in cirrhosis Cirrhosis →
- Primary hyperaldosteronism
- Oedema in nephrotic syndrome when other measures fail
Adverse effects
Common
- Gynecomastia and breast pain
- Menstrual irregularities and reduced libido
- Hyperkalaemia
- Hyponatraemia and dehydration
- Nausea and diarrhoea
Contraindications
- Hyperkalaemia
- Addison's disease
- Concomitant use of eplerenone
Key interactions
- ACE inhibitors, ARBs, potassium supplements, heparin or trimethoprim
- Risk of severe hyperkalaemia
- NSAIDs
- Less diuretic effect and more hyperkalaemia
- Lithium
- Less lithium clearance and risk of toxicity
- Digoxin
- Can interfere with some digoxin level assays
- Mitotane
- Spironolactone lowers mitotane levels; the combination is avoided
What is monitored
- Potassium within the first week and then regularly
- Creatinine and kidney function
- Sodium
- Blood pressure and volume status
Nursing care
- Before giving: potassium and kidney function; hold and report if potassium is high.
- Watch for signs of hyperkalaemia: muscle weakness, slow pulse, palpitations.
- Daily weight and abdominal girth in ascites.
- Teach: avoid potassium salt substitutes and potassium supplements unless prescribed; take it consistently with or without food; report breast tenderness.
Pregnancy and breastfeeding
Generally avoided: in animal studies it feminised male fetuses, and it blocks androgen effects.
Test yourself
Think of the answer, then tap the question to see it.
How does spironolactone spare potassium?
It blocks the aldosterone receptor in the collecting duct, so fewer ENaC channels and Na⁺/K⁺ pumps are made; less sodium enters and less potassium is secreted.
Why does spironolactone cause gynecomastia?
Besides the mineralocorticoid receptor it blocks androgen receptors, and it shifts the androgen-to-oestrogen balance.
Can you name three contraindications of spironolactone?
Hyperkalaemia, Addison's disease and use together with eplerenone.
Why does spironolactone suit cirrhotic ascites?
In cirrhosis aldosterone is high (secondary hyperaldosteronism) and drives sodium retention; blocking its receptor removes that sodium where it is retained.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - SPIRONOLACTONE tablet (DailyMed (U.S. National Library of Medicine), 2026); Spironolactone: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.