Cardiovascular / Renal
Spironolactone
Aldosterone (mineralocorticoid) antagonist — A potassium-sparing diuretic used in heart failure, resistant hypertension and fluid from liver disease.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
Spironolactone blocks aldosterone and is used in heart failure (where it improves outcomes), resistant hypertension, and the fluid retention (ascites/oedema) of liver disease.
How it works
By blocking aldosterone in the kidney it promotes loss of sodium and water while retaining potassium, and in the heart and vessels it counters the harmful remodelling that aldosterone drives.
In practice
In practice the dominant concern is potassium: spironolactone raises it, and the risk compounds with ACE inhibitors, ARBs, renal impairment and potassium supplements — so check potassium and renal function before starting and after changes. It has a strong evidence base in heart failure and resistant hypertension. Counsel men about possible breast tenderness, a recognised hormonal effect.
Examples
Practical use
How to take it & use it well
- Take spironolactone once daily, ideally in the morning, and with or after food to reduce stomach upset.
- Take it at the same time each day to keep your routine steady.
- Keep up with blood tests, which check your potassium level and kidney function.
- If you miss a dose, take it when you remember unless the next is nearly due, then skip it; do not double up.
- Avoid potassium-based salt substitutes and high-potassium supplements unless advised, as this medicine raises potassium.
- Tell your team if you become very unwell with vomiting or diarrhoea, as this can affect your salts and kidneys.
Common uses
- Heart failure with reduced ejection fraction
- Resistant hypertension
- Ascites and oedema in liver disease
- Primary hyperaldosteronism
Monitoring
- Potassium and renal function before and regularly after starting or up-titrating
- Blood pressure and fluid status
- Hormonal side-effects
Weighing it up
Advantages & disadvantages
Advantages
- It removes excess fluid while holding on to potassium, unlike many other water tablets.
- It helps in heart failure and can improve outcomes in suitable people.
- It is used for fluid retention, high blood pressure and some hormone-related conditions.
- It is taken just once a day.
- It is well established and inexpensive.
Disadvantages
- It can raise potassium to harmful levels, which needs regular blood tests.
- It can cause breast tenderness or enlargement, particularly in men.
- It can cause light-headedness, especially when standing.
- It is less suitable if kidney function is significantly reduced.
- It may cause stomach upset, which taking it with food can ease.
Key safety principles
What to watch for
- Hyperkalaemia — the key risk, magnified by ACE inhibitors/ARBs, renal impairment and potassium supplements.
- Caution in significant renal impairment.
- Hormonal effects such as breast tenderness/enlargement (less with eplerenone).
Key interactions
What to avoid or check alongside
- Other medicines that raise potassium, including some blood-pressure drugs and potassium supplements, can together push potassium dangerously high.
- Potassium-containing salt substitutes add to the risk of high potassium.
- Anti-inflammatory painkillers can reduce its effect and strain the kidneys.
- Other blood-pressure-lowering medicines can add to dizziness and low blood pressure.
- Lithium levels can rise with this medicine, needing monitoring.
Patient & carer advice
- Avoid potassium-based salt substitutes
- Attend your blood tests — potassium needs watching
- Report breast tenderness; an alternative may be available
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
Spironolactone: frequently asked questions
Why do I need regular blood tests?
Spironolactone can raise potassium and affect the kidneys, so blood tests check these are staying safe, especially after starting or a dose change.
Can I use a low-sodium salt substitute?
Usually not, because many salt substitutes are high in potassium and this medicine already raises potassium. Check with your pharmacist before using one.
Why might it affect breast tissue?
Spironolactone can have hormone-related effects, which sometimes cause breast tenderness or enlargement, more often in men. Tell your prescriber if this troubles you.
Is it a normal water tablet?
It removes fluid like other water tablets but is potassium-sparing, meaning it holds on to potassium rather than losing it, which is why monitoring differs.
When is the best time to take it?
Taking it in the morning helps avoid extra night-time toilet trips, and taking it with or after food can reduce stomach upset.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
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