Pharmacology · Topic 76 of 102
Potassium-Sparing Diuretics
Loop diuretics waste potassium.
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Potassium-Sparing Diuretics
(Spironolactone, eplerenone) Weak diuretics that keep potassium. High K⁺ is the danger.
Zooming into the kidney onto one nephron, down to the collecting duct. A potassium-sparing diuretic plugs the swap in the duct wall that would send sodium back into the blood and potassium out into the urine. So sodium and water ride on down the duct and leave in the urine, and the potassium stays in the blood. The blood potassium climbs from 4.2 to 5.6, above the normal 3.5 to 5.0: hyperkalemia is the danger.
- A K⁺-sparing drug blocks the swapNurse seesoften paired with a loop or thiazideNurse doescheck K⁺ before giving
- Na⁺ and water leave in the urine; K⁺ staysNurse seesurine output upNurse doesno K⁺ supplements, no salt substitutes
- K⁺ climbs: hyperkalemia is the dangerNurse seesK⁺ above 5.0Nurse doeshold the dose and notify
normal K⁺ 3.5–5.0 mEq/L · above 5.0: hold the dose and notify · check K⁺ before giving
they are potassium chloride · no potassium supplements unless the provider orders them
it blocks male hormones · eplerenone is much less likely to cause it — the usual switch
Used for · don't give
IndicationsUsed for
Don't give / use caution
How it works
Collecting ductThey act at the late distal tubule and collecting duct: sodium and water leave, potassium stays
Side effects
What you'll seeHigh potassium is the danger
High K⁺ on the monitor
ECGA live monitor strip of hyperkalemia: T waves that are tall, narrow and pointed (peaked).
Labs & monitoring
CheckCheck potassium and kidney function: at baseline, within 1 week, then regularly
Red flags
Hold + notifyGiving it
Every doseCheck K⁺ first — above 5.0, hold the dose and notify
In HFrEF it helps patients live longer.
Gynecomastia, breast tendernessSelective, so gynecomastia is much less likely — not impossible.
Block the sodium channel directly — the same high-K⁺ danger.
More detail
Nursing priorities
In orderLoop or K⁺-sparing?
Don't confuse| Examples | Spironolactone, eplerenone, amiloride, triamterene |
|---|---|
| Works in | The late distal tubule and collecting duct |
| Strength | Weak alone — paired with a loop or thiazide |
| Potassium | Keeps K⁺: hyperkalemia |
| Hold if | K⁺ above 5.0 · hold + notify |
| ECG | Tall, peaked T waves |
| Food | No extra potassium foods, no salt substitutes |
| Its own effect | Gynecomastia (spironolactone) |
Teach your patient
At homeK⁺-sparing keeps potassium: above 5.0, hold the dose and call. No salt substitutes — they are potassium chloride. The opposite of a loop.
Sources · Spironolactone tablets label (DailyMed) · Amiloride hydrochloride tablets label (DailyMed) · StatPearls: Therapeutic Uses of Diuretic Agents (NCBI Bookshelf) · OpenStax Pharmacology for Nurses 34.4: Potassium-Sparing Diuretics · OpenStax Medical-Surgical Nursing 10.3: Electrolyte Imbalance · Films: the NurseSavvy learning-flow visuals. Follow your facility’s protocol.
Potassium-Sparing Diuretics
Loop diuretics waste potassium. Potassium-sparing diuretics do the opposite — but that protective effect becomes dangerous the moment you stop paying attention to K+ levels.
Potassium-sparing diuretics act on the distal convoluted tubule and collecting duct to promote sodium and water excretion while retaining potassium. There are two subclasses with different mechanisms. Aldosterone antagonists (spironolactone, eplerenone) block aldosterone receptors, preventing sodium reabsorption and potassium secretion. Epithelial sodium channel (ENaC) blockers (amiloride, triamterene) directly block sodium channels, reducing the electrochemical gradient that drives potassium loss. These are weak diuretics on their own, so they're usually paired with thiazides or loop diuretics to counterbalance potassium wasting. Spironolactone has a unique secondary role: it reduces mortality in heart failure with reduced ejection fraction (HFrEF) by blocking aldosterone's fibrotic effects on the heart. The critical nursing concern is hyperkalemia — serum K+ above 5.0 mEq/L. Risk escalates when the patient is also taking ACE inhibitors, ARBs, or potassium supplements. You monitor potassium levels at baseline and regularly during therapy, watch for signs of hyperkalemia (muscle weakness, peaked T waves, bradycardia), and teach the patient to avoid salt substitutes, which contain potassium chloride.
Key Distinctions
Don't confuse spironolactone's antiandrogenic side effects (gynecomastia, menstrual irregularities) with eplerenone, which is selective and avoids these effects. Students often pair potassium-sparing diuretics with potassium supplements — this combination is contraindicated. Unlike loop diuretics that cause hypokalemia, potassium-sparing diuretics cause hyperkalemia — the electrolyte risk runs in the opposite direction.
Clinical Pearl
Salt substitutes are secret potassium bombs. A patient on spironolactone who switches to 'low-sodium' salt at home is self-supplementing potassium without knowing it.
Knowledge Check
3 quick questions on the must-knows for this topic.
What electrolyte problem do these diuretics risk?
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