Potassium-Sparing Diuretic / Mineralocorticoid Receptor Antagonist Pregnancy: Spironolactone or its metabolites may cross the placental barrier; feminisation has been observed in male rat fetuses. Use in pregnancy only if the anticipated benefit outweighs the possible hazard to mother and fetus. Metabolites detected in breast milk — if treatment is considered essential, use an alternative method of infant feeding (eMC §4.6).

Spironolactone

Brand names: Aldactone

Spironolactone is a potassium-sparing diuretic and aldosterone antagonist used in heart failure, resistant hypertension, ascites and oedema due to liver disease, and primary hyperaldosteronism.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Congestive cardiac failure with oedema: initially 100 mg daily (range 25–200 mg daily)

Route: oral

Frequency: once daily or in divided doses, taken with a meal

Max: Indication-specific ranges up to 400 mg/day (hepatic cirrhosis with ascites, malignant ascites, primary aldosteronism)

General medicine variant — same UK SPC (§4.2) as the base spironolactone entry. Adults — Congestive cardiac failure with oedema: initial 100 mg daily (single or divided doses), range 25–200 mg daily; maintenance individualised. Hepatic cirrhosis with ascites and oedema: 100 mg/day if urinary Na+/K+ ratio >1.0, or 200–400 mg/day if ratio <1.0. Malignant ascites: initially 100–200 mg/day, increased gradually up to 400 mg/day in severe cases. Nephrotic syndrome: 100–200 mg/day. Primary aldosteronism: diagnostic — 400 mg/day (long test 3–4 weeks; short test 4 days); pre-surgery 100–400 mg/day. Severe heart failure (NYHA III–IV, RALES): initiate 25 mg once daily if serum potassium ≤5.0 mEq/L and serum creatinine ≤2.5 mg/dL; titrate to 50 mg once daily if tolerated, or reduce to 25 mg every other day. Elderly: start with the lowest dose and titrate up; caution in severe hepatic/renal impairment. Paediatric (per SPC §4.2): initial daily dosage 1–3 mg/kg body weight in divided doses under paediatric specialist guidance only — verify paediatric dosing against a children's formulary. Administer once daily with a meal. US labelling additionally lists essential hypertension: initial 25–100 mg daily in single or divided doses.

Dose adjustments

Renal

Contraindicated in acute renal insufficiency, significant renal compromise or anuria; use with care in severe renal impairment (eMC). For heart failure, US labelling: eGFR >50 start 25 mg once daily; eGFR 30–50 consider 25 mg every other day owing to hyperkalaemia risk. Monitor serum potassium and creatinine (1 week after initiation/dose increase, then periodically).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Acute renal insufficiency, significant renal compromise or anuria
Addison's disease
Hyperkalaemia
Hypersensitivity to spironolactone or any excipient
Concomitant use of eplerenone or other potassium-sparing diuretics
Paediatric patients with moderate to severe renal impairment

Side effects

Gynaecomastia (dose- and duration-related; usually reversible); breast pain
Hyperkalaemia; electrolyte imbalance
Menstrual disorder; libido disorder
Nausea; gastrointestinal disorder
Dizziness; malaise

Interactions

Drugs/conditions causing hyperkalaemia — ACE inhibitors, angiotensin II receptor antagonists, other potassium-sparing diuretics, potassium supplements, NSAIDs, heparin/low molecular weight heparin, potassium-containing salt substitutes — risk of severe hyperkalaemia
Trimethoprim/sulfamethoxazole (co-trimoxazole) — may cause clinically relevant hyperkalaemia
Digoxin — spironolactone increases serum digoxin concentration and interferes with certain serum digoxin assays
Lithium — reduced renal clearance and increased risk of lithium toxicity (US labelling §7.2)

Clinical monograph

How it works

It competitively antagonises aldosterone at the distal renal tubule, promoting sodium and water excretion while conserving potassium.

Prescribing in practice

Hyperkalaemia is the most important risk, particularly with renal impairment, ACE inhibitors, angiotensin receptor blockers or potassium supplements, so monitor potassium closely.
It can cause gynaecomastia, breast tenderness and menstrual disturbance because of its anti-androgenic activity.
Monitor renal function, as the combination of renal impairment and other renin-angiotensin agents increases the risk of dangerous hyperkalaemia and acute kidney injury.

Monitoring

Check renal function and serum potassium before starting and regularly during treatment, especially after dose changes or when combined with other agents affecting potassium.

Counselling the patient

Avoid potassium-containing salt substitutes and supplements unless advised.
Report breast swelling or tenderness, which may improve on stopping.
Attend for the blood tests that check your kidneys and potassium.

Evidence & guidelines

Spironolactone improves outcomes in heart failure with reduced ejection fraction, as shown by the RALES trial and reflected in NICE guidance.

Reference: RALES Trial (Pitt et al, NEJM 1999); ESC Heart Failure Guidelines 2021; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways