In a patient with chronic heart failure with reduced ejection fraction who is already on guideline‑directed therapy (angiotensin‑converting enzyme inhibitor or angiotensin receptor blocker/angiotensin receptor‑neprilysin inhibitor, beta‑blocker, and a diuretic), which mineralocorticoid receptor antagonist should be used first‑line, spironolactone or eplerenone?

Choice of Mineralocorticoid Receptor Antagonist in HFrEF

Either spironolactone or eplerenone is acceptable as first-line MRA therapy in HFrEF, as both reduce mortality and hospitalization when added to ACE inhibitor and beta-blocker therapy; however, spironolactone is typically preferred due to stronger evidence, lower cost, and broader availability, while eplerenone should be chosen specifically for men who develop gynecomastia or breast discomfort on spironolactone. 1

Guideline Recommendations

The European Society of Cardiology guidelines provide Class I, Level A recommendations for MRA therapy in HFrEF but do not mandate one agent over the other. 1 Both drugs are recommended for patients with HFrEF who remain symptomatic (NYHA class II-IV) despite treatment with an ACE inhibitor and beta-blocker, to reduce the risk of heart failure hospitalization and death. 1

Evidence Base for Each Agent

Spironolactone

• The RALES trial established spironolactone's mortality benefit in advanced heart failure (NYHA class III-IV), though notably patients in this trial received almost no beta-blockers. 1, 2
• Recommended starting dose is 12.5-25 mg daily, with target dose of 25-50 mg daily. 1
• Spironolactone has been in clinical use longer and has more extensive real-world experience. 1

Eplerenone

• The EMPHASIS-HF trial demonstrated eplerenone's efficacy in mild-to-moderate heart failure (NYHA class II), with patients receiving contemporary background therapy including beta-blockers. 1
• Target dose is 50 mg daily. 1
• Eplerenone has greater mineralocorticoid receptor selectivity, resulting in lower rates of gynecomastia and breast discomfort compared to spironolactone. 1

Practical Selection Algorithm

Start with spironolactone 12.5-25 mg daily in the following situations: 1

• Initial MRA therapy in any patient with HFrEF
• Cost is a significant consideration
• Female patients (gynecomastia not a concern)

Switch to or initiate eplerenone 25 mg daily when: 1

• Male patient develops breast discomfort or gynecomastia on spironolactone
• Patient specifically requests the more selective agent

Critical Monitoring Requirements

Both agents require identical monitoring protocols: 1

Initial monitoring:

• Check potassium and creatinine at 1 week and 4 weeks after starting or increasing dose
• Continue checks at 8 weeks, 12 weeks, then at 6,9, and 12 months
• Subsequently monitor every 4 months

Dose adjustment thresholds:

• If K+ rises above 5.5 mmol/L or creatinine rises to 221 μmol/L (2.5 mg/dL) or eGFR <30 mL/min/1.73 m²: halve the dose and monitor closely 1
• If K+ rises to >6.0 mmol/L or creatinine >310 μmol/L (3.5 mg/dL) or eGFR <20 mL/min/1.73 m²: stop MRA immediately and seek specialist advice 1

Common Pitfalls and How to Avoid Them

Hyperkalaemia risk is the primary concern and occurs more commonly in clinical practice than in clinical trials. 1 To minimize risk:

• Never combine MRA with both ACE inhibitor AND ARB - this triple combination dramatically increases hyperkalaemia and renal dysfunction risk and is explicitly not recommended. 1
• Avoid potassium-sparing diuretics (amiloride, triamterene) when using MRA. 1
• Avoid NSAIDs, which increase hyperkalaemia and renal dysfunction risk. 1
• Warn patients about "low-salt" substitutes with high potassium content. 1
• If diarrhea or vomiting occurs, patients should stop the MRA and contact their physician immediately. 1

Underutilization is widespread: Recent registry data show only 35-46% of eligible HFrEF patients receive MRA therapy, even >12 months after diagnosis. 3 This represents a major treatment gap, as MRA therapy should be initiated within 2-4 weeks of diagnosis as part of rapid foundational therapy sequencing. 4, 5

Target dose matters less than initiation: Low starting doses (spironolactone 12.5-25 mg or eplerenone 25 mg) provide substantial therapeutic benefit, and achieving low doses of all four foundational drug classes (ARNI/ACE-I, beta-blocker, MRA, SGLT2 inhibitor) should take precedence over up-titration to target doses. 4

Sequencing Within Foundational Therapy

MRA should typically be initiated 1-2 weeks after starting sacubitril/valsartan (or ACE inhibitor) in a rapid sequencing strategy, as the earlier agents can enhance tolerability. 4, 5 However, in patients with advanced CKD (stage IV), extreme caution is warranted, and MRA may need to be avoided entirely due to prohibitive hyperkalaemia risk when combined with ARNI therapy. 6