Pharmacology · Potassium-sparing diuretics
Amiloride !
A potassium-sparing diuretic that blocks the ENaC sodium channel. Usually combined with a thiazide or loop diuretic to prevent low potassium.
Updated 2026-11-01
Mechanism of action
Amiloride plugs the epithelial sodium channel (ENaC) on the luminal side of the late distal tubule and collecting duct. Less sodium enters the cell, the lumen becomes less negative, and less potassium and hydrogen are secreted. It does not depend on aldosterone.
- Amiloride blocks ENaC in the collecting duct
- Less sodium enters the cell
- The lumen is less negative: K⁺ and H⁺ are retained
- Weak diuresis that spares potassium
Pharmacokinetics
- Metabolism
- Not metabolised by the liver
- Elimination
- Excreted unchanged by the kidneys, with part in the stool
- Onset and duration
- Begins within about 2 hours; the effect peaks at 6 to 10 hours and lasts about 24 hours
Indications
- Heart failure, with a thiazide or loop diuretic, to prevent or correct low potassium Heart failure →
- Hypertension, with a thiazide, to prevent low potassium Arterial hypertension →
Adverse effects
Common
- Hyperkalaemia
- Nausea, loss of appetite, diarrhoea
- Headache
- Muscle cramps
Contraindications
- Hyperkalaemia
- Other potassium-sparing agents or potassium supplements
- Anuria, acute or chronic kidney failure
- Diabetic nephropathy
- Hypersensitivity to amiloride
Key interactions
- Potassium supplements or salt substitutes
- Severe hyperkalaemia
- Spironolactone or triamterene
- Severe hyperkalaemia; not combined
- ACE inhibitors, ARBs, ciclosporin or tacrolimus
- Higher risk of hyperkalaemia
- Lithium
- Less lithium clearance and risk of toxicity
What is monitored
- Serum potassium, often at the start and after any change
- Kidney function
- Sodium
- Blood glucose in diabetes
Nursing care
- Before giving: potassium and kidney function; hold and report if potassium is high.
- Watch for signs of hyperkalaemia: weakness, numbness, slow or irregular pulse.
- Ask about potassium supplements and salt substitutes.
- Teach: avoid potassium salt substitutes, report weakness or palpitations.
Pregnancy and breastfeeding
Used only if clearly needed; diuretics do not prevent pre-eclampsia.
Test yourself
Think of the answer, then tap the question to see it.
Where and how does amiloride act?
It blocks the epithelial sodium channel (ENaC) on the luminal side of the collecting duct, independently of aldosterone.
Why is amiloride usually combined with a thiazide?
Alone it is a weak diuretic; with a thiazide it adds to the diuresis and prevents the thiazide's potassium loss.
Which patients have a higher risk of hyperkalaemia with amiloride?
People with kidney impairment, diabetes or older age, and those taking potassium supplements, ACE inhibitors or ARBs.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - AMILORIDE HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); Amiloride: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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