2.2.3 Potassium-sparing diuretics and aldosterone antagonists

These agents have a weak diuretic effect if given alone but their effects are additive with thiazides and loop diuretics.
Amiloride is usually reserved for those already receiving thiazide or loop diuretics in whom hypokalaemia is a concern. Amiloride may take 2 to 3 days for full effect.
Amiloride is also used in resistant hypertension under specialist supervision.
Spironolactone may be associated with significant hyperkalaemia or renal impairment particularly in combination with ACE inhibitors, angiotensin-II receptors, angiotensin receptor/neprilysin inhibitor, or other diuretics. U&Es should be checked at baseline, 1 week after initiation (and after every dose increase), monthly for first 3 months, then every 3 months for 1 year, and then every 6 months thereafter. Patients should be warned of the risk of hyperkalaemia in the setting of volume depletion and of the signs and symptoms of hyperkalaemia. See MHRA for further information.
Eplerenone is less likely to produce sexual side effects such as gynaecomastia, breast pain or menstrual irregularities.
Finerenone is available for patients who meet criteria in NICE TA877. See NI Managed Entry decisions.
Counsel patients on ‘sick day guidance’ with diuretics.
Diuretics should not be used on a long term basis to treat simple gravitational oedema. This will usually respond to increased ambulation, raising the legs and support stockings.

Cautions

Potassium-sparing diuretics and MRAs should be used with caution in renal impairment.
Elderly patients are particularly susceptible to the side-effects of diuretics, including increased risk of postural hypotension, collapse and falls. Confusion, dehydration, urinary incontinence and hyponatraemia may be particular problems.
Caution with concurrent NSAID due to risk of acute kidney injury (avoid over-the-counter use of NSAIDs).
Potassium-sparing diuretics should be used with caution when co-administered with ACE inhibitors or angiotensin-II receptor antagonists due to the risk of hyperkalaemia. See BNF for other interactions e.g. trimethoprim, clarithromycin.
Potassium supplements should not (unless under close supervision and monitoring) be given with: potassium sparing diuretics, MRAs, in the presence of renal failure, with ACE inhibitors or with angiotensin-II receptor antagonists, due to the danger of hyperkalaemia. Ask about potassium-containing salt substitutes that a patient may be taking: one serving of common salt substitutes can contain around the potassium content of one oral potassium supplement tablet.