Furosemide

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Furosemide on Prescriptsy

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Furosemide is a powerful loop diuretic used to treat fluid retention (oedema) caused by heart failure, liver cirrhosis, and kidney disease.

It is also used in the management of high blood pressure (hypertension).

Furosemide works by acting on the kidneys to increase the production of urine, removing excess fluid and sodium from the body.

It is one of the most commonly prescribed medicines in the United Kingdom and is available as tablets, oral solution, and injection.

Furosemide is a prescription-only medicine (POM) and is listed in the British National Formulary (BNF) as an essential medicine in the management of fluid overload.

This page provides a comprehensive clinical overview of furosemide, including how it works, who needs it, dosing guidance, potential side effects, important safety warnings, and how to obtain a prescription in the UK.

Important safety information about furosemide

• Furosemide is a prescription-only medicine (POM) that requires regular medical monitoring.
• Take furosemide in the morning to avoid night-time disruption from increased urination.
• Regular blood tests for kidney function and electrolytes (especially potassium) are essential.
• Do not stop furosemide suddenly without medical advice, particularly if you take it for heart failure.
• During illness with vomiting, diarrhoea, or fever, contact your GP about sick-day rules for diuretics.

Understanding fluid retention and its causes

Oedema is the medical term for swelling caused by excess fluid trapped in the body's tissues.

It most commonly affects the legs, ankles, and feet (peripheral oedema), but can also involve the lungs (pulmonary oedema) and abdomen (ascites).

The underlying causes of oedema relate to an imbalance between the forces that move fluid from the blood vessels into the tissues and the mechanisms that return it.

Heart failure is the most common cause of oedema requiring diuretic treatment in the UK.

When the heart cannot pump efficiently, blood backs up in the venous system, increasing hydrostatic pressure in the capillaries and forcing fluid into the surrounding tissues.

Approximately 920,000 people in the UK live with heart failure, and the condition accounts for around 5% of all emergency hospital admissions.

The symptoms of fluid overload in heart failure include breathlessness (particularly on exertion and when lying flat), ankle swelling, weight gain, and fatigue.

Liver cirrhosis causes fluid retention through a combination of mechanisms: reduced production of albumin (the main protein that holds fluid in the blood vessels), portal hypertension (increased pressure in the liver's blood supply), and activation of sodium-retaining hormones.

Ascites, the accumulation of fluid in the abdominal cavity, is one of the most common complications of advanced liver disease and affects approximately 50% of patients with cirrhosis within 10 years of diagnosis.

Chronic kidney disease can cause oedema when the kidneys lose their ability to excrete sodium and water effectively.

Nephrotic syndrome, a condition characterised by heavy protein loss in the urine, causes severe oedema through reduced oncotic pressure in the blood.

In these patients, furosemide may be required at higher than usual doses because kidney damage reduces the drug's delivery to its site of action in the tubules.

How furosemide works: mechanism of action

Furosemide acts on the thick ascending limb of the loop of Henle in the kidney, a segment responsible for reabsorbing approximately 25% of filtered sodium.

It inhibits the sodium-potassium-chloride co-transporter (NKCC2) on the luminal surface of tubular cells, blocking the reabsorption of sodium, potassium, and chloride into the blood.

This results in a powerful diuresis, with significantly increased excretion of sodium, water, potassium, chloride, calcium, and magnesium.

The diuretic effect of furosemide is substantially more potent than that of thiazide diuretics (such as bendroflumethiazide and indapamide), which act on the distal convoluted tubule and inhibit only about 5% of sodium reabsorption.

This makes furosemide the preferred diuretic for managing significant fluid overload, pulmonary oedema, and oedema resistant to thiazide therapy.

After oral administration, the onset of diuresis occurs within 30 to 60 minutes, peaks at 1 to 2 hours, and lasts approximately 4 to 6 hours.

This relatively short duration of action means that excess fluid is removed during the daytime, allowing patients to sleep undisturbed at night if the medicine is taken in the morning.

Furosemide also has a direct venodilatory effect that is independent of its diuretic action.

In acute heart failure, intravenous furosemide produces venous pooling within minutes, reducing preload (the volume of blood returning to the heart) and providing rapid symptom relief from pulmonary oedema before significant urine output occurs.

Clinical evidence and UK prescribing guidance

Furosemide has been in clinical use since the 1960s and is one of the most extensively studied medicines in cardiovascular and renal medicine.

It is listed on the World Health Organisation Model List of Essential Medicines and is the most frequently prescribed loop diuretic in the UK NHS.

NICE guideline NG106 on chronic heart failure recommends diuretics for all patients with signs and symptoms of fluid congestion.

While diuretics do not improve survival in heart failure (unlike ACE inhibitors, beta-blockers, and mineralocorticoid receptor antagonists), they are essential for symptom control and quality of life.

The guideline advises titrating the diuretic dose to achieve and maintain the patient's target (dry) weight, using the lowest dose that keeps the patient free of oedema.

The BNF lists furosemide as the standard loop diuretic for oedema in heart failure, liver disease, and renal disease.

It notes that oral furosemide can produce up to 2 litres of urine within 6 hours of a single dose in patients with normal kidney function and significant fluid overload.

For resistant oedema, the BNF recommends using furosemide in combination with a thiazide diuretic (sequential nephron blockade), but this approach requires close monitoring due to the risk of profound electrolyte disturbances.

For hypertension, NICE guideline NG136 does not recommend loop diuretics as first-line treatment.

Thiazide-like diuretics (indapamide or chlorthalidone) are preferred for blood pressure lowering, as they provide smoother 24-hour blood pressure reduction.

However, furosemide may be used in hypertensive patients who also require diuretic treatment for concurrent oedema.

Furosemide compared with other diuretics

Bumetanide is another loop diuretic with a similar mechanism of action to furosemide.

Bumetanide has a more predictable oral bioavailability (approximately 80 to 90% compared with furosemide's highly variable 40 to 70%), which may make it preferable in patients with unpredictable responses to oral furosemide, particularly those with gut oedema from right heart failure.

The BNF notes that 1 mg bumetanide is approximately equivalent to 40 mg furosemide.

Torasemide is a loop diuretic with a longer duration of action and more consistent oral absorption than furosemide.

Some studies suggest potential advantages in heart failure outcomes, but torasemide is less widely prescribed in UK practice and evidence of superiority remains inconclusive.

Thiazide and thiazide-like diuretics (bendroflumethiazide, indapamide, chlorthalidone) have a weaker diuretic effect but a more prolonged duration of action.

They are the preferred diuretics for treating hypertension but are insufficient for managing significant oedema in heart failure or liver disease.

When combined with furosemide (sequential nephron blockade), they can overcome diuretic resistance, but this combination carries a high risk of electrolyte depletion and requires careful specialist supervision.

Dosage and administration

The dose of furosemide depends on the condition being treated, the severity of fluid retention, and the patient's kidney function.

For mild to moderate oedema, the usual starting dose is 20 to 40 mg once daily in the morning.

The dose is adjusted based on clinical response, aiming for a gradual reduction in weight and oedema without causing excessive dehydration.

For heart failure, doses of 40 to 80 mg daily are common, with some patients requiring up to 160 mg daily or more under specialist care.

In chronic kidney disease, much higher doses may be needed because impaired tubular secretion reduces the amount of furosemide reaching its site of action in the loop of Henle.

Doses of 250 mg or more daily are sometimes required in consultation with a nephrologist.

In liver cirrhosis, furosemide is usually combined with spironolactone, starting with furosemide 40 mg and spironolactone 100 mg daily, with adjustment based on weight, fluid balance, and electrolytes.

Take furosemide in the morning.

If a second dose is prescribed, take it at lunchtime or early afternoon rather than in the evening, to avoid night-time disturbance from increased urination.

Swallow tablets with water. If you miss a morning dose, take it as soon as you remember, provided it is before 4 pm.

After 4 pm, skip the missed dose and resume the next morning. Never double the dose.

Side effects of furosemide

Electrolyte and metabolic effects

The most important and common adverse effects of furosemide are electrolyte disturbances.

Hypokalaemia is a key concern and can cause muscle cramps, weakness, cardiac arrhythmias, and enhance the toxicity of digoxin. Hyponatraemia, hypomagnesaemia, and hypocalcaemia can also occur.

Regular blood monitoring is essential. Hyperuricaemia may precipitate gout. Hyperglycaemia may affect diabetes control.

Volume-related effects

Dehydration and orthostatic hypotension (dizziness on standing) are common, particularly in elderly patients and during hot weather.

Excessive diuresis can cause acute kidney injury, particularly in patients who are already taking ACE inhibitors or NSAIDs.

Patients should be advised to maintain adequate fluid intake and to follow sick-day rules during illness.

Other side effects

Ototoxicity (hearing disturbance, tinnitus) can occur, particularly with high intravenous doses or in patients with renal impairment.

Rare adverse effects include blood dyscrasias, severe skin reactions, pancreatitis, and interstitial nephritis.

Contact your GP or call NHS 111 if you develop unusual bruising, sore throat, skin rash, severe abdominal pain, or hearing changes.

Call 999 if you experience severe breathlessness, chest pain, or collapse. Report any suspected adverse reactions to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Furosemide is contraindicated in anuria, severe dehydration, severe hypokalaemia or hyponatraemia, and in hepatic coma or pre-coma.

It should be used with caution in patients with prostatic enlargement or urinary retention, as rapid diuresis may precipitate acute urinary obstruction.

Patients taking digoxin must maintain normal potassium levels to avoid potentially fatal toxicity.

Drug interactions are clinically important.

Avoid concurrent NSAIDs (which reduce diuretic effect and increase renal risk), exercise caution when starting ACE inhibitors (risk of first-dose hypotension), and monitor lithium levels closely if co-prescribed.

Aminoglycoside antibiotics (gentamicin, amikacin) increase the risk of ototoxicity when combined with furosemide.

Elderly patients are at increased risk of dehydration, falls, electrolyte disturbances, and acute kidney injury during diuretic treatment.

The lowest effective dose should be used, and patients should be reviewed regularly. During acute illness or hot weather, temporary dose reduction may be necessary.

Furosemide should be used in pregnancy only if the benefit outweighs the risk, as it crosses the placenta. It is excreted in breast milk and may suppress lactation. Discuss alternatives with your prescriber if you are pregnant or breastfeeding.

How to get furosemide in the UK

Furosemide is a prescription-only medicine available on the NHS.

Your GP or hospital specialist can prescribe it following a clinical assessment that includes blood pressure measurement, examination for signs of fluid overload, and baseline blood tests.

Furosemide is very inexpensive and widely available as a generic medicine in the UK.

Authorised online prescribers registered with the General Pharmaceutical Council (GPhC) can also prescribe furosemide following an appropriate clinical consultation. The NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Living with diuretic treatment

If you take furosemide for heart failure, you may be asked to weigh yourself daily at the same time each morning.

An increase of 1.5 to 2 kg over 2 to 3 days may indicate fluid accumulation and should be reported to your GP or heart failure nurse.

You may be given a flexible diuretic plan that allows you to adjust your dose within a specified range based on your daily weight and symptoms.

Follow your healthcare team's instructions carefully and attend all scheduled reviews.

Stay adequately hydrated but do not drink excessively. Follow any fluid restriction guidance given by your prescriber, particularly if you have heart failure or liver disease.

Eat a balanced diet that includes potassium-rich foods (bananas, oranges, potatoes, tomatoes, spinach) unless you have been advised to restrict potassium by your kidney specialist.

Limit salt intake to help control fluid retention. Avoid excessive alcohol, which can worsen dehydration and interact with diuretic therapy.

Sources

• Furosemide 40 mg Tablets, Summary of Product Characteristics (EMC)
• Furosemide, British National Formulary (BNF)
• NICE NG106: Chronic heart failure in adults: diagnosis and management
• NICE NG136: Hypertension in adults: diagnosis and management
• Furosemide, NHS
• MHRA Yellow Card Scheme