Furosemid

Furosemide is a potent loop diuretic that acts on the ascending limb of the loop of Henle in the nephron by inhibiting the sodium-potassium-chloride co-transporter (NKCC2).

This produces a rapid, intense, and relatively short-lasting diuresis.

Furosemide is licensed for the treatment of oedema associated with congestive heart failure, hepatic cirrhosis, and renal disease (including nephrotic syndrome), as well as for the acute management of pulmonary oedema and resistant hypertension.

It is one of the most widely prescribed diuretics globally and is listed as an essential medicine by the WHO.

The BNF recommends furosemide as a first-line loop diuretic for fluid overload in heart failure.

Onset of action is approximately 30-60 minutes after oral administration, with peak diuresis at 1-2 hours and a duration of approximately 4-6 hours.

The relatively short action allows flexible dosing to suit patient lifestyle. Furosemide may also be used in urgent clinical settings via intravenous administration for rapid fluid removal.

Take furosemide in the morning to minimise nocturnal diuresis and sleep disturbance. If a second daily dose is required, take it by early afternoon (no later than 2 pm).

Swallow tablets whole with water. Furosemide can be taken with or without food, though food may slightly delay absorption without affecting overall bioavailability.

Maintain adequate fluid intake unless advised otherwise by your prescriber.

Weigh yourself regularly (at the same time each day) to monitor fluid balance; report sudden weight gain of more than 2 kg in 2-3 days to your doctor.

Do not stop furosemide abruptly in heart failure, as this may cause fluid reaccumulation.

Oedema: Initial dose 40 mg in the morning. May be adjusted to 20-80 mg daily depending on response.

In resistant oedema, doses up to 160 mg daily (in divided doses) may be required under specialist supervision.

Pulmonary oedema (acute): 40-80 mg intravenously, repeated as clinically necessary.

Hypertension: 40-80 mg daily, though loop diuretics are not first-line antihypertensives.

In renal impairment, higher doses may be required to achieve adequate diuresis (up to 250-500 mg daily under specialist care). Elderly patients should be started on the lowest effective dose.

Electrolytes and renal function must be monitored regularly, particularly potassium, sodium, and creatinine.

Side effects are categorised per SmPC and pharmacovigilance data.

Very common (≥1/10): Electrolyte disturbances (hypokalaemia, hyponatraemia, hypochloraemia, hypomagnesaemia), dehydration, hypovolaemia (especially in elderly patients).

Common (≥1/100 to <1/10): Hypotension (including postural), dizziness, headache, nausea, increased serum creatinine, increased serum uric acid (may precipitate gout), hyperglycaemia.

Uncommon (≥1/1,000 to <1/100): Tinnitus and hearing impairment (usually reversible, more common with rapid intravenous administration), pruritus, urticaria, rash, photosensitivity, blurred vision, paraesthesia.

Rare (≥1/10,000 to <1/1,000): Ototoxicity (irreversible at very high doses), pancreatitis, cholestasis, interstitial nephritis, agranulocytosis, thrombocytopenia, aplastic anaemia, Stevens-Johnson syndrome.

Hypokalaemia is the most clinically significant electrolyte disturbance and may cause muscle cramps, weakness, cardiac arrhythmias, and potentiate digoxin toxicity.

Regular monitoring of serum electrolytes (potassium, sodium, magnesium, calcium), renal function (creatinine, urea), and blood glucose is essential.

Potassium supplementation or the addition of a potassium-sparing diuretic may be required.

Furosemide potentiates the ototoxic effects of aminoglycoside antibiotics; avoid concurrent use where possible. NSAIDs reduce the diuretic response and may worsen renal function; use with caution.

Furosemide can exacerbate gout by raising serum uric acid. In patients with hepatic cirrhosis, electrolyte imbalance may precipitate hepatic encephalopathy.

Prostatic hypertrophy or urinary tract obstruction should be excluded before initiation, as rapid diuresis can cause acute urinary retention.

Furosemide is contraindicated in patients with anuria or severe renal failure unresponsive to furosemide challenge, pre-comatose or comatose states associated with hepatic encephalopathy, severe hypokalaemia or hyponatraemia, hypovolaemia or dehydration, hypersensitivity to furosemide or sulphonamides (cross-sensitivity exists), and Addison's disease.

It should be used with extreme caution in patients concurrently receiving lithium (risk of lithium toxicity).