Loop Diuretic Pregnancy: Use with caution — furosemide crosses placenta. Risk of electrolyte imbalance in fetus. Avoid in first trimester; use only if clearly indicated in second/third trimester.

Furosemide (Ascites / Cirrhosis)

Brand names: Lasix, Frusemide

Adult dose

Dose: Ascites in cirrhosis: 40mg once daily (combined with spironolactone 100mg OD in 100:40 ratio). Increase both drugs maintaining ratio if insufficient response. Oedema: 20–80mg OD or BD. Acute pulmonary oedema (IV): 40–80mg IV over 1–2 minutes; repeat after 1 hour if needed.

Route: Oral or IV

Frequency: Once daily (morning — avoid afternoon/evening to prevent nocturia)

Max: 160mg/day (cirrhotic ascites combined therapy); 2g/day (renal failure)

Always take in the morning. IV infusion: administer at a maximum rate of 4mg/minute (ototoxicity risk at higher rates). Oral bioavailability ~50% — double oral dose when converting from IV to oral. Combined with spironolactone in 100:40 ratio for cirrhotic ascites — do not use furosemide alone (risk of severe hyponatraemia).

Paediatric dose

Dose: 0.5 mg/kg

Route: Oral or IV

Frequency: Two to three times daily

Max: 2mg/kg per dose (max 80mg per dose)

BNF for Children: Oral: 0.5–2mg/kg BD–TDS (max 80mg per dose). IV: 0.5–1mg/kg (max 40mg) over 5 minutes — repeat every 6–8 hours if needed. Neonates: 0.5–1mg/kg every 12–24 hours. Source: BNF for Children 2024.

Dose adjustments

Renal

Higher doses required in renal impairment (loop diuretics retain efficacy but dose must be increased). Avoid with aminoglycosides (additive nephrotoxicity and ototoxicity).

Hepatic

Use with caution — electrolyte disturbances may precipitate hepatic encephalopathy. Target maximum 0.5kg/day weight loss in cirrhosis without peripheral oedema.

Paediatric weight-based calculator

Patient weight (kg)

Clinical pearls

Cirrhosis ratio rule: furosemide and spironolactone are always used in a 40:100mg ratio (furo:spiro). This maintains electrolyte neutrality. Furosemide alone causes severe hyponatraemia in cirrhosis.
IV rate limit: furosemide IV must not exceed 4mg/minute — faster rates cause sensorineural hearing loss (permanent ototoxicity).
Oral to IV conversion: furosemide oral bioavailability is ~50%. If converting from oral to IV, halve the dose (e.g., oral 80mg → IV 40mg).
Antidote for overdose: IV fluid resuscitation with normal saline; correct electrolytes. No specific antidote.

Contraindications

Anuria
Severe hypokalaemia or hyponatraemia
Dehydration
Addison's disease
Comatose states associated with liver cirrhosis (relative — use with extreme caution)

Side effects

Hypokalaemia (most common — add potassium supplementation or combine with spironolactone)
Hyponatraemia (especially in cirrhosis — restrict furosemide if Na⁺ <125mmol/L)
Hypomagnesaemia
Dehydration and pre-renal azotaemia
Ototoxicity (at high IV doses or with rapid infusion — especially with concomitant aminoglycosides)
Hyperglycaemia (mild)
Gout (hyperuricaemia)

Interactions

Aminoglycosides (gentamicin, amikacin): additive ototoxicity and nephrotoxicity — avoid combination where possible
ACE inhibitors / ARBs: additive hypotension and acute kidney injury risk — monitor renal function
NSAIDs: reduce diuretic efficacy and worsen renal function in cirrhosis
Lithium: furosemide increases lithium levels — monitor lithium levels
Digoxin: hypokalaemia from furosemide increases digoxin toxicity risk — monitor K⁺ and digoxin levels

Monitoring

Serum electrolytes (Na⁺, K⁺, Mg²⁺) — minimum twice weekly in cirrhotic ascites
Renal function (U&E, creatinine)
Weight (daily in inpatients)
Blood pressure
Hearing (if high-dose IV prolonged use)

Reference: BNFc; BNF 90; EASL Cirrhosis Guidelines 2018; Baveno VII Consensus 2022; BNF for Children 2024. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

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