What are Mineralocorticoid Receptor Antagonists (MRAs)?

Mineralocorticoid Receptor Antagonists (MRAs)

Mineralocorticoid receptor antagonists (MRAs) are specific pharmacologic antagonists of aldosterone that act primarily through competitive binding of receptors at the aldosterone-dependent sodium-potassium exchange site in the distal convoluted renal tubule. 1

Mechanism of Action

MRAs work by:

• Blocking the binding of aldosterone to mineralocorticoid receptors 1, 2
• Causing increased sodium and water excretion while retaining potassium 1
• Counteracting secondary aldosteronism in edematous states such as congestive heart failure, hepatic cirrhosis, and nephrotic syndrome 1

Types of MRAs

There are two main classes of MRAs:

1. Steroidal MRAs:

   • Spironolactone: First-generation MRA, less selective
   • Eplerenone: Second-generation MRA, more selective with fewer endocrine side effects

2. Non-steroidal MRAs:

   • Finerenone: Newer agent with potentially different tissue distribution and side effect profile 3

Clinical Indications

MRAs are recommended for:

1. Heart Failure with Reduced Ejection Fraction (HFrEF):

   • Class I recommendation for patients with NYHA class II-IV symptoms and LVEF ≤35% 3, 4
   • Significantly reduces mortality and morbidity when added to standard therapy 3
   • Demonstrated in landmark trials: RALES (spironolactone), EPHESUS and EMPHASIS-HF (eplerenone) 3, 5

2. Resistant Hypertension:

   • Recommended for patients not meeting blood pressure targets on three classes of antihypertensive medications (including a diuretic) 3, 4
   • Effective when added to existing treatment with ACE inhibitor/ARB, thiazide-like diuretic, and dihydropyridine calcium channel blocker 3

3. Diabetic Kidney Disease:

   • Indicated for patients with type 2 diabetes, eGFR ≥25 ml/min/1.73 m², normal serum potassium, and albuminuria 3, 4
   • Reduces albuminuria and provides cardiovascular benefits 3

Dosing and Administration

• Spironolactone:

  • Starting dose: 25 mg once daily 4
  • Target dose: 50 mg once daily after 4 weeks if serum potassium <5.0 mEq/L 4

• Eplerenone:

  • Starting dose: 25 mg once daily
  • Target dose: 50 mg once daily

• Dose adjustments:

  • For patients with eGFR 31-49 mL/min/1.73 m², reduce dose by half 4

Monitoring Requirements

1. Initial monitoring:

   • Check serum potassium and renal function within 1-2 weeks after initiation 4
   • Repeat at 4 weeks after initiation or dose change 4

2. Long-term monitoring:

   • Every 6 months once stable 4
   • More frequent testing for clinical instability or risk factors for hyperkalemia

Safety Considerations and Contraindications

Major Risk: Hyperkalemia

• Adding an MRA to ACE inhibitor or ARB therapy significantly increases hyperkalemia risk 3
• Risk of hyperkalemia is doubled compared to placebo (odds ratio 2.27) 5
• Serious hyperkalemia (K+ >6.0 mmol/L) occurs in approximately 2.9% of patients 5

Contraindications:

• eGFR <30 mL/min/1.73 m² 4
• Serum potassium ≥5.0 mEq/L 4
• Creatinine >2.5 mg/dL for men or >2.0 mg/dL for women 3

Management of Hyperkalemia:

• For K+ >5.5 mmol/L: Halve the dose and monitor closely 3
• For K+ >6.0 mmol/L: Discontinue MRA therapy 3

Clinical Efficacy

• HFrEF: MRAs reduce the risk of cardiovascular death or heart failure hospitalization by 34% (HR 0.66) 5
• HFpEF/HFmrEF: MRAs reduce heart failure hospitalizations (HR 0.82) but have less impact on mortality 5
• Resistant Hypertension: Effective for blood pressure control and may provide additional cardiovascular benefits 6

Common Pitfalls and Caveats

1. Underutilization: Despite strong evidence and guideline recommendations, MRAs remain underutilized in eligible patients 7

2. Inappropriate monitoring: Failure to monitor serum potassium and renal function can lead to preventable adverse events

3. Drug interactions: Concomitant use with potassium supplements, potassium-sparing diuretics, or high-potassium diets can increase hyperkalemia risk 1

4. Combination therapy risks: Combination of MRAs with both ACE inhibitors and ARBs should be avoided due to excessive hyperkalemia risk 4

5. Patient selection: Careful adherence to guideline-recommended inclusion and exclusion criteria is essential to minimize risks 7

By understanding the mechanism, indications, and safety considerations of MRAs, clinicians can optimize their use to improve outcomes in heart failure, resistant hypertension, and diabetic kidney disease while minimizing adverse effects.