Potassium-Sparing Diuretic (Epithelial Sodium Channel Blocker)

Amiloride Hydrochloride

Brand names: Midamor

Adult dose

Dose: 5–20 mg daily; usually 5 mg once daily

Route: Oral

Frequency: Once daily in the morning

Clinical pearls

Most commonly used in combination with thiazide or loop diuretics to prevent hypokalaemia
Also used in Conn's syndrome (primary hyperaldosteronism) as adjunct or alternative to spironolactone
Acts on collecting duct ENaC channels — unlike spironolactone, not an aldosterone antagonist
Does not have anti-androgenic side effects (unlike spironolactone)
Requires careful monitoring of electrolytes — especially if combined with RAAS inhibitors
Useful in Liddle syndrome (specific ENaC mutation causing hypertension)

Contraindications

Hyperkalaemia (K⁺ >5.5 mmol/L)
Severe renal impairment (eGFR <30) — accumulation and hyperkalaemia risk
Addison's disease
Concomitant potassium supplements or potassium-sparing diuretics (without monitoring)

Side effects

Hyperkalaemia (most serious — especially with renal impairment or ACE inhibitors/ARBs)
Hyponatraemia
Nausea
Diarrhoea
Headache
Dizziness

Interactions

ACE inhibitors/ARBs — potentiate hyperkalaemia; monitor K⁺ closely
Potassium supplements — avoid concurrent use
NSAIDs — reduce diuretic efficacy and worsen renal function
Lithium — amiloride reduces lithium reabsorption; may lower lithium levels
Trimethoprim — additive hyperkalaemia risk

Monitoring

Serum potassium and sodium at baseline, 1–2 weeks after initiation, then 3–6 monthly
eGFR at baseline and periodically
Blood pressure

Reference: BNF; NICE NG136 (Chronic kidney disease: managing hyperkalaemia, 2020); NICE NG133 (Hypertension in adults, 2019 updated 2023); https://bnf.nice.org.uk/drugs/amiloride-hydrochloride/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways