Classification and Mechanism
ENaC blockers are potassium-sparing diuretics that work by directly inhibiting the epithelial sodium channel in the distal collecting duct of the kidney 1, 4. This mechanism is distinct from mineralocorticoid receptor antagonists (MRAs) like spironolactone and eplerenone, which indirectly affect ENaC through aldosterone receptor blockade 1.
The Two ENaC Blockers:
Amiloride: The most studied ENaC blocker, typically dosed at 5-20 mg daily 5, 6. It has been shown to ameliorate both hypertension and hypokalemia in patients with primary aldosteronism, though it is less efficacious than spironolactone 1.
Triamterene: Dosed at 50-200 mg daily in divided doses 5, 6. Like amiloride, it blocks ENaC directly but is less extensively studied in clinical trials 1.
Clinical Context and Positioning
ENaC blockers are generally used as second-line or add-on therapy rather than first-line treatment 1, 2. The 2025 Endocrine Society guidelines specifically suggest using MRAs rather than ENaC inhibitors for primary aldosteronism treatment 2.
Key Clinical Advantages:
- Lack sex steroid-related side effects that occur with spironolactone (gynecomastia, menstrual irregularities) 1
- Generally well tolerated with similar safety profiles to MRAs 1, 7
- Useful in specific populations, particularly when spironolactone is contraindicated or not tolerated 2
Important Distinction from MRAs:
While both ENaC blockers and MRAs are "potassium-sparing diuretics," they work through different mechanisms 1, 4. In nephrotic syndrome, amiloride is actually preferable to spironolactone because urinary proteases can directly activate ENaC independent of mineralocorticoid receptors 8.
Practical Prescribing Considerations
Monitor serum potassium closely, especially when combining with ACE inhibitors, ARBs, or in patients with chronic kidney disease 1, 3. The risk of hyperkalemia increases significantly with these combinations 7, 9.
Avoid in advanced renal impairment (eGFR <30 mL/min/1.73m²) due to hyperkalemia risk 1, 10.
Comparative Efficacy:
Studies in resistant hypertension show amiloride reduces systolic/diastolic blood pressure by approximately 12/5 mm Hg when added to existing therapy 7. In direct comparisons, amiloride and spironolactone demonstrate similar blood pressure-lowering effects, though spironolactone may have additional benefits on endothelial function 1, 2.
Common Pitfall
Do not confuse ENaC blockers with MRAs - they are both potassium-sparing but mechanistically distinct 1, 4. This distinction matters clinically, particularly in conditions like nephrotic syndrome where ENaC is directly activated by urinary proteases 8.