Aldosterone antagonist (potassium-sparing diuretic) 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 an aldosterone antagonist (potassium-sparing diuretic) used here as add-on therapy in heart failure, as well as for resistant hypertension and oedema; this page is framed for older patients.

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: Severe heart failure (NYHA III–IV): 25 mg once daily initially, increased to 50 mg once daily if tolerated

Route: oral

Frequency: once daily, taken with a meal

Max: 50 mg once daily (severe heart failure regimen; higher doses apply to other indications)

Heart-failure-context variant. UK SPC §4.2 — severe heart failure (NYHA III–IV), based on RALES: initiate spironolactone 25 mg once daily if serum potassium ≤5.0 mEq/L and serum creatinine ≤2.5 mg/dL; patients who tolerate 25 mg once daily may increase to 50 mg once daily as clinically indicated; patients who do not tolerate 25 mg once daily may reduce to 25 mg every other day. Monitoring (§4.4): serum potassium and creatinine 1 week after initiation/dose increase, monthly for the first 3 months, then quarterly for a year, then every 6 months; discontinue or interrupt treatment if serum potassium exceeds 5 mEq/L or serum creatinine exceeds 4 mg/dL. Avoid other potassium-sparing diuretics and avoid oral potassium supplements. Congestive cardiac failure with oedema (same SPC): initial 100 mg daily, range 25–200 mg daily. US labelling (heart failure): eGFR >50 start 25 mg once daily; eGFR 30–50 consider 25 mg every other day owing to hyperkalaemia risk. Paediatric (per SPC §4.2): 1–3 mg/kg body weight daily in divided doses under paediatric specialist guidance only — verify paediatric dosing against a children's formulary.

Dose adjustments

Renal

Contraindicated in acute renal insufficiency, significant renal compromise or anuria; use with care in severe renal impairment. In heart failure, US labelling: eGFR >50 start 25 mg once daily; eGFR 30–50 consider 25 mg every other day. Monitor serum potassium and creatinine closely; discontinue/interrupt if potassium exceeds 5 mEq/L or creatinine exceeds 4 mg/dL.

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

Hyperkalaemia (may be fatal in severe heart failure); electrolyte imbalance
Gynaecomastia (dose- and duration-related; usually reversible); breast pain
Menstrual disorder; libido disorder
Nausea; gastrointestinal disorder
Dizziness; acute kidney injury; 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 retaining potassium, and reduces aldosterone-mediated cardiac remodelling in heart failure.

Prescribing in practice

Hyperkalaemia is the key hazard, especially in older people and those with renal impairment or on ACE inhibitors, ARBs or potassium supplements, so check renal function and potassium before and during treatment and avoid in significant renal impairment or pre-existing high potassium.
It can cause gynaecomastia and breast tenderness, which may limit tolerability.
Combine cautiously with other drugs affecting potassium or renal function, and review NSAID use.

Monitoring

Monitor renal function and serum potassium at baseline, shortly after starting and after dose changes, with closer review in older or renally impaired patients.

Counselling the patient

Avoid potassium-containing salt substitutes and report muscle weakness or palpitations.
Report breast swelling or tenderness, which can occur.

Evidence & guidelines

The RALES trial demonstrated that spironolactone reduced mortality in severe heart failure, and NICE recommends mineralocorticoid receptor antagonists as add-on therapy in HFrEF.

Reference: RALES trial; NICE NG106; ESC HF Guidelines; 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