Spironolactone with furosemide

How it works

Furosemide inhibits the Na-K-2Cl co-transporter in the loop of Henle to produce a strong diuresis, while spironolactone blocks aldosterone receptors in the distal nephron to add diuresis and offset the potassium loss caused by the loop component.

Prescribing in practice

• Potassium can move in either direction, so the key risk is dysregulation — hyperkalaemia from spironolactone (heightened by renal impairment, ACE inhibitors, ARBs or potassium supplements) or hypokalaemia if the loop effect dominates.
• The combination can cause marked volume depletion, hypotension and renal impairment, particularly in the elderly or when intercurrent illness reduces intake.
• Spironolactone may cause gynaecomastia and is contraindicated in Addison's disease, while furosemide carries a risk of ototoxicity with rapid administration or high exposure.

Monitoring

Monitor serum potassium, sodium, renal function and fluid status before starting and regularly during treatment, and review more closely during intercurrent illness.

Counselling the patient

• Report vomiting, diarrhoea or reduced fluid intake, as a short break may be needed.
• Mention breast tenderness or swelling (a possible spironolactone effect).
• Keep up with the blood tests for your kidneys and potassium.

Evidence & guidelines

The diuretic and electrolyte effects of combining an aldosterone antagonist with a loop diuretic are well established, and RALES established the survival benefit of spironolactone in heart failure when added to standard therapy.