Loop diuretics
ATC code: C03CA01 (Furosemide)
Brand names
Lasix
Blocks the Na+/K+/2Cl- cotransporter in the thick ascending limb of the loop of Henle. This is the most potent diuretic effect among available agents. Increases excretion of sodium, chloride, potassium, magnesium, calcium, and water. Onset 5 minutes after intravenous administration, peak 30 minutes, duration 2 hours. Oral onset 30-60 minutes, duration 6-8 hours. Oral bioavailability is unpredictable (10-90%).
First line
For acute cardiogenic pulmonary edema, intravenous furosemide 20-40 mg (higher if already on chronic therapy) is part of emergency treatment alongside seated positioning, oxygen, nitrates, and non-invasive ventilation. Recommended by ESC HF 2021 and ACC/AHA/HFSA 2022.
First line
Furosemide and its analogues (torsemide, bumetanide) are the mainstay of symptomatic edema management in HF. ESC HF 2021, ACC/AHA/HFSA 2022, and NICE NG106 recommend loop diuretics as drugs of choice in patients with congestion symptoms. They do not improve survival but rapidly relieve dyspnea and edema. Doses are individualised by weight, symptoms, and renal function. Torsemide has more predictable bioavailability and is preferred to furosemide in many countries.
Starting dose in HF is 20-40 mg orally once daily, titrated as needed. For acute decompensated HF, intravenous boluses or infusion are used. Dose is adjusted by weight and diuresis.
First line
In nephrotic syndrome, high-dose furosemide is used, often intravenously and combined with a thiazide diuretic to overcome diuretic resistance. Supported by KDIGO 2021 and UpToDate.
Not recommended
For ordinary hypertension, furosemide is rarely prescribed and not recommended as a first choice. ESC/ESH 2024, ACC/AHA 2017, and NICE NG136 prefer thiazide-like diuretics (indapamide, chlorthalidone) because of a smoother antihypertensive effect and less potassium loss. Furosemide is used in hypertensive patients with marked HF or impaired renal function (eGFR < 30).
Not recommended
Furosemide is sometimes taken 'after a drinking episode' to reduce puffiness. In reality a hangover involves dehydration, not fluid overload – a diuretic worsens the state. Evidence-based measures are water, salt, and simple food. Combining furosemide with alcohol raises hypotension, electrolyte disturbance, and syncope risk.
Not recommended
Furosemide is sometimes used for 'rapid weight loss' – the effect is fluid loss, not fat loss. This is clinically dangerous: dehydration, electrolyte disturbance (hypokalaemia, hyponatraemia), acute kidney injury, and hypotension. International obesity guidelines (NICE NG189, AHA/ACC/TOS) do not include diuretics. Bodybuilders use furosemide for pre-contest 'cutting' – a practice associated with arrhythmia deaths.
Crosses the placenta. Chronic use outside vital indications causes electrolyte disturbances in mother and fetus. Used only for vital indications, such as acute pulmonary edema in pregnancy.
Passes into breast milk and may suppress lactation. Generally compatible with breastfeeding for short courses; long-term use requires individual decision-making.
Furosemide is evaluated for the following indications with varying evidence strength: Acute pulmonary edema (evidence tier A), Edema in nephrotic syndrome (evidence tier A), Edema in heart failure (evidence tier A). See the full indication matrix with dosing and citations above on this page.
Common side effects of Furosemide (≥ 1 in 100): Hypokalaemia, hypomagnesaemia, hyponatraemia, Dehydration with rapid diuresis, Orthostatic hypotension, Hyperuricaemia and gout exacerbation, Modest increases in glucose and lipids. See the Safety section for uncommon and serious reactions.
Crosses the placenta. Chronic use outside vital indications causes electrolyte disturbances in mother and fetus. Used only for vital indications, such as acute pulmonary edema in pregnancy.
Passes into breast milk and may suppress lactation. Generally compatible with breastfeeding for short courses; long-term use requires individual decision-making.
Furosemide is contraindicated in: Hypersensitivity to furosemide or sulfonamides; Anuria and acute renal failure unresponsive to furosemide; Severe hypokalaemia, hyponatraemia, hypovolaemia, dehydration; Hepatic precoma and coma; Pregnancy – used only for vital indications. Full list in the Safety section.