Furosemide (Frusemide)

How it works

It inhibits the sodium-potassium-chloride co-transporter in the thick ascending limb of the loop of Henle, producing potent natriuresis and diuresis.

Prescribing in practice

• Older patients are prone to dehydration, hypotension, acute kidney injury and falls, so use the lowest effective dose, monitor volume status, and reassess during intercurrent illness using sick-day guidance.
• It can cause hypokalaemia, hyponatraemia and hypomagnesaemia, and worsens gout and glucose control; review potassium-affecting and nephrotoxic co-medications.
• High doses or rapid intravenous administration carry a risk of ototoxicity, particularly with renal impairment or other ototoxic drugs.

Monitoring

Monitor renal function, electrolytes, blood pressure, weight and fluid status, especially after dose changes or during acute illness.

Counselling the patient

• Take earlier in the day to avoid night-time urination disturbing sleep.
• Report dizziness, cramps, marked weakness or reduced urine output.
• During vomiting, diarrhoea or fever, seek advice as the dose may need pausing.

Evidence & guidelines

Loop diuretics are a long-established cornerstone of symptomatic congestion relief in heart failure, with cautious dosing in older adults supported by their pharmacology and electrolyte effects.