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Loop diuretic Pregnancy: Frusol must not be given during pregnancy unless there are compelling medical reasons. Breast-feeding: furosemide may inhibit lactation and may pass into breast milk — women must not breastfeed if they are treated with furosemide (breast-feeding is listed as a contraindication in §4.3).

Furosemide (Frusemide)

Brand names: Lasix, Frusol

Used in: Liver Disease & Cirrhosis Acute Kidney Injury

Furosemide (frusemide) is a loop diuretic used for oedema in heart failure, renal and hepatic disease and for fluid overload; in older people the risks of dehydration, electrolyte disturbance and falls are heightened.

Adult dose

Dose: Prompt diuresis — oedema (cardiac, pulmonary, hepatic and renal), peripheral oedema due to mechanical obstruction or venous insufficiency, and hypertension: the usual initial daily dose is 40 mg ORALLY. This may be adjusted until an effective dose is achieved. SCOPE OF THIS FIGURE: it is the ORAL dose, taken from a UK oral-solution SPC (Frusol Oral Solution, 'For oral use') — see sourceUsed for the exact product. The intravenous route also shown on this page is NOT covered by this source and NO IV dose is published here — obtain IV dosing from a UK furosemide injection SPC.
Route: Oral. The SPC states 'For oral use. Suitable for administration via nasogastric (NG) or percutaneous endoscopic gastrostomy (PEG) tubes.' Intravenous and intramuscular dosing are not covered by this source.
Frequency: The SPC expresses the dose as a DAILY dose and directs that 'The medication should be administered in the morning to avoid nocturnal diuresis.' In the elderly, furosemide is generally eliminated more slowly and the dosage should be titrated until the required response is achieved.
INDICATION CONFIRMED BY §4.1 (newly captured): 'Furosemide is indicated in all conditions requiring prompt diuresis, including cardiac, pulmonary, hepatic and renal oedema, peripheral oedema due to mechanical obstruction or venous insufficiency and hypertension. It is also indicated for the maintenance therapy of mild oedema of any origin.' A later matcher fix swapped the product to a UK ORAL SPC, so the oral route is now properly UK-sourced — but the swap lost the injection licence, so the page's IV route is now the unsourced half. Only the oral subset is published, and the scope is stated inside the dose text above. NO ADULT CEILING IS PUBLISHED: §4.2 gives no maximum adult dose — only an initial dose that is titrated. ⚠️ The '40 mg/day' maximum that appears in §4.2 is the PAEDIATRIC maximum total dose and must NOT be read as an adult ceiling; it has deliberately not been placed in a maxDose field, because it coincides with the adult STARTING dose and would falsely cap adult titration. ELDERLY (this page's population): §4.4 flags 'elderly patients (lower initial dose as particularly susceptible to side-effects - see section 4.2)', but §4.2 itself gives no lower elderly number, so no elderly starting figure is published here — titrate as above. §4.4 also warns that symptomatic hypotension leading to dizziness, fainting or loss of consciousness can occur particularly in the elderly, that furosemide is not recommended in elderly patients with dementia taking risperidone (increased mortality), and that a lower dose should be considered where there is difficulty with micturition including prostatic hypertrophy. CORRECT BEFORE STARTING: hypotension, hypovolaemia, and severe electrolyte disturbances (particularly hypokalaemia, hyponatraemia and acid-base disturbances). EXCIPIENT: this oral solution contains 79.5 mg of alcohol (ethanol) in each ml. Some sections of the product information we used were incomplete — check the full SPC.

Paediatric dose

Dose: 1 to 3 mg/kg body weight DAILY (this is a DAILY TOTAL, not a per-dose figure), up to a maximum total dose of 40 mg/day
Route: Oral — this SPC is an oral solution and states 'For oral use'
Frequency: Expressed by the SPC as a daily total; the medication should be administered in the morning to avoid nocturnal diuresis
Max: 40 mg/day — the SPC's stated maximum total daily dose for the paediatric population
§4.2 Paediatric population, verbatim and in full: '1 to 3mg/Kg body weight daily up to a maximum total dose of 40mg/day.' ⚠️ THIS IS A DAILY TOTAL. It must never be entered or read as a per-dose amount — doing so would give a several-fold overdose. `dosePerKg` is deliberately left null for two reasons: the label gives a RANGE (1–3) that cannot be collapsed into one number, and leaving it null keeps the weight-based dose calculator from mounting a per-dose multiplication on a daily figure. This page is the geriatrics/elderly furosemide entry; the paediatric figure is reproduced only because it is the label's own, and any paediatric use should be verified against a children's formulary. §4.4 also warns that in premature infants there is a risk of nephrocalcinosis / nephrolithiasis, so renal function must be monitored and renal ultrasonography performed.

Dose adjustments

Renal

Contraindicated in impaired renal function with a creatinine clearance below 30 ml/min per 1.73 m² body surface area, and in anuria or renal failure with anuria not responding to furosemide. §4.2 gives no numeric renal dose reduction. Frequent checks of serum potassium are necessary where creatinine clearance is below 60 ml/min per 1.73 m². Marked diuresis can cause reversible impairment of kidney function in patients with renal dysfunction — adequate fluid intake is necessary. Serum creatinine and urea levels tend to rise during treatment.

Hepatic

Contraindicated in comatose or pre-comatose states associated with hepatic cirrhosis or encephalopathy. In moderate liver congestion dosage adjustment may be needed. Impaired hepatic function — hepatic failure and alcoholic cirrhosis particularly predispose to hypokalaemia and hypomagnesaemia, so monitoring is required. §4.2 gives no numeric hepatic dose reduction.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients listed in section 6.1, or to sulphonamides / sulphonamide derivatives
  • Hypovolaemia and dehydration (with or without accompanying hypotension)
  • Severe hypokalaemia; severe hyponatraemia
  • Comatose or pre-comatose states associated with hepatic cirrhosis or encephalopathy
  • Anuria, or renal failure with anuria not responding to furosemide; renal failure as a result of poisoning by nephrotoxic or hepatotoxic agents
  • Impaired renal function with a creatinine clearance below 30 ml/min per 1.73 m² body surface area
  • Addison's disease
  • Digitalis intoxication
  • Concomitant potassium supplements or potassium-sparing diuretics
  • Breast-feeding women

Side effects

  • Very common: dehydration, hyponatraemia, hypochloraemic metabolic alkalosis, hypocalcaemia, hypomagnesaemia
  • Very common: hypotension — if pronounced may cause impairment of concentration and reactions, light-headedness, sensations of pressure in the head, headache, drowsiness, weakness, disorders of vision, dry mouth and orthostatic intolerance
  • Common: hypovolaemia, hypochloraemia
  • Uncommon: impaired glucose tolerance, hyperuricaemia, gout, reduced serum HDL-cholesterol, raised serum LDL-cholesterol and triglycerides, hyperglycaemia
  • Uncommon: dry mouth, thirst, nausea, bowel motility disturbances, vomiting, diarrhoea, constipation
  • Uncommon: deafness (sometimes irreversible); rare: tinnitus and reversible or irreversible loss of hearing, particularly in patients with renal failure or hypoproteinaemia
  • Uncommon: visual disturbance, blurred vision, yellow vision
  • Uncommon: orthostatic intolerance, cardiac arrhythmias; increased risk or persistence of patent ductus arteriosus in premature infants
  • Uncommon: aplastic anaemia; rare: bone marrow depression (necessitates withdrawal of treatment), eosinophilia, leucopenia; very rare: haemolytic anaemia, agranulocytosis, thrombocytopenia
  • Rare: paraesthesia, confusion, headache; not known: dizziness, fainting and loss of consciousness caused by symptomatic hypotension
  • Rare: acute pancreatitis in long-term diuretic treatment; rare: intrahepatic cholestasis (jaundice), abnormal hepatic function; frequency not known: hepatic encephalopathy
  • Rare: vasculitis, thrombosis, shock
  • Very rare: tetany. Frequency not known: increased potassium excretion and aggravation of pre-existing metabolic alkalosis in decompensated cirrhosis
  • This side-effect list may be incomplete — check the full SPC.

Monitoring

  • Correct hypotension, hypovolaemia and severe electrolyte disturbances (particularly hypokalaemia, hyponatraemia and acid-base disturbances) BEFORE furosemide is started
  • Serum sodium — particularly in the elderly or in patients liable to electrolyte deficiency
  • Serum potassium — regular monitoring, with a potassium supplement if necessary, is recommended in all cases and is essential at higher doses and in impaired renal function; especially important with concomitant digoxin, as potassium deficiency can trigger or exacerbate digitalis intoxication. A potassium-rich diet is recommended during long-term use
  • Frequent serum potassium checks where creatinine clearance is below 60 ml/min per 1.73 m², or where furosemide is combined with drugs that may raise potassium
  • Renal function — frequent BUN in the first few months of treatment and periodically thereafter; measure BUN regularly on long-term or high-dose treatment. Ensure adequate fluid intake in renal dysfunction
  • Blood glucose — regular monitoring is desirable, as latent diabetes may become overt and insulin requirements in established diabetes may increase; stop furosemide before a glucose tolerance test
  • Other electrolytes — during long-term therapy, especially at high doses, measure magnesium, calcium, chloride, bicarbonate and uric acid regularly
  • Serum cholesterol and triglycerides may rise but usually return to normal within 6 months of starting furosemide
  • Regular clinical monitoring for blood dyscrasias (stop furosemide immediately if these occur), liver damage and idiosyncratic reactions
  • Elderly: watch for symptomatic hypotension causing dizziness, fainting or loss of consciousness, particularly with other hypotensive medicines
  • Avoid concurrent NSAIDs where possible (the diuretic effect may be attenuated); with ACE inhibitors or angiotensin II receptor antagonists severe hypotension may occur — reduce or stop furosemide for 3 days before starting or increasing those drugs
  • Do not use in elderly patients with dementia taking risperidone — increased mortality has been reported
  • Consider a lower dose and monitor closely in difficulty with micturition including prostatic hypertrophy (risk of urinary retention), and in partial occlusion of the urinary tract
  • Premature infants — monitor renal function and perform renal ultrasonography, because of the risk of nephrocalcinosis / nephrolithiasis
  • This list may be incomplete — check the full SPC.

Clinical monograph

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.

Reference: NICE NG106 Heart Failure; ESC HF Guidelines 2021; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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