Furosemide is a strong diuretic used to remove excess fluid from the body, for example in heart failure or kidney disease. It can lower potassium and blood pressure too much, so regular blood tests are important.
Also known as: Lasix
Furosemide-induced hypokalaemia increases Digoxin toxicity.
Furosemide is a loop diuretic that depletes potassium and magnesium, the electrolytes that most influence digitalis toxicity. Hypokalaemia increases digoxin binding to Na+/K+-ATPase and potentiates arrhythmias, even at therapeutic levels. This is a classic combination in heart failure patients, who use both drugs together. Monitor serum potassium (keep ≥ 4.0 mEq/L) and magnesium, correct deficits, monitor the ECG and consider digoxin level monitoring in unstable patients.
Loop diuretic + digoxin: diuretic-induced hypokalaemia and hypomagnesaemia increase digitalis toxicity. Monitor electrolytes and ECG.
Renal potassium loss sensitises the myocardium to Digoxin.
Electrolytes and digoxin levels; ECG if symptoms occur.
Nausea, anorexia, bradycardia, arrhythmias, confusion.
Monitor K+ and replace early; adjust the Digoxin dose if renal function changes.
DailyMed/FDA (NIH/NLM) — approved Digoxin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5886e233-b2da-4acb-be05-9bf40fb8e7f4 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cdcd001-ab4b-4210-a455-2e17a7bc4972
Calcitriol + loop diuretic: opposing effects on serum calcium.
Calcitriol (active vitamin D) increases intestinal calcium absorption and tends to raise serum calcium, while furosemide increases urinary calcium excretion and tends to lower it. The effects are opposing and, in practice, the combination is sometimes used (for example, in hypercalcaemia with hypercalciuria), but requires monitoring: furosemide can mask calcitriol-induced hypercalcaemia or, in dehydrated patients, precipitate hypocalcaemia. Monitor serum calcium, magnesium and renal function, and adjust doses according to therapeutic goals.
Calcitriol + loop diuretic: opposing effects on serum calcium. Monitor calcium and renal function.
Furosemide increases renal calcium excretion, partially counteracting calcitriol.
Serum calcium on long-term therapy.
Cramps, paraesthesia (hypocalcaemia).
Monitor serum calcium on prolonged combination, especially in renal impairment.
DailyMed (FDA) — approved Calcitriol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8465337c-86ca-ea9d-e053-2991aa0ab167 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Furosemide + magnesium: furosemide increases renal magnesium loss.
Loop diuretics (furosemide) increase renal excretion of magnesium (and potassium), potentially causing hypomagnesaemia in patients on prolonged or high-dose treatment. Hypomagnesaemia is clinically relevant in itself (weakness, tetany, arrhythmias) and because it potentiates digitalis toxicity and hypokalaemia. In patients receiving magnesium sulfate (infusion or oral replacement) with furosemide, monitor serum magnesium and potassium, correct deficits and periodically reassess the need for the diuretic and the replacement.
Furosemide + magnesium: furosemide increases renal magnesium loss — risk of hypomagnesaemia.
Loop diuretics increase urinary magnesium excretion; supplementation corrects the deficit but requires monitoring.
Serum magnesium and renal function.
Weakness, cramps, arrhythmias.
Monitor serum magnesium during supplementation in patients on diuretics.
DailyMed (FDA) — approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 ; approved Magnesium sulfate label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a5a9f565-639c-4b22-b9e5-718bac7cfcf3 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Corticosteroid + loop diuretic: additive hypokalaemia risk.
Furosemide causes renal potassium loss (hypokalaemia, hypochloraemic alkalosis), and systemic corticosteroids such as dexamethasone increase potassium excretion and can cause hypokalaemic alkalosis, especially at high doses. Together, the risk of hypokalaemia is additive, with potential for arrhythmias, particularly in patients with cardiac disease, the elderly or those on other potassium-lowering drugs. The furosemide and corticosteroid labels recommend monitoring serum electrolytes and considering potassium supplementation during the combination.
Dexamethasone + furosemide: additive risk of hypokalaemia and hypokalaemic alkalosis. Monitor potassium and ECG.
Both increase renal potassium loss.
Serum potassium and hypokalaemia symptoms.
Weakness, cramps, arrhythmias.
Monitor serum potassium; consider supplementation if needed.
DailyMed (FDA) — approved Dexamethasone label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cbd9005-7df2-47ee-adb3-7244c1c69bc3 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Loop-diuretic hypokalaemia raises the risk of torsades de pointes with sotalol.
Sotalol prolongs the QT interval and the risk of torsades de pointes rises as serum potassium (and magnesium) fall. Furosemide, by depleting these electrolytes, creates the electrophysiological environment for potentially fatal polymorphic ventricular arrhythmias. The combination is not prohibited but demands discipline: correct potassium to at least 4.0 mEq/L before starting sotalol, correct hypomagnesaemia, monitor the QT and electrolytes during treatment and avoid other QT-prolonging drugs.
Loop diuretic + sotalol: diuretic-induced hypokalaemia/hypomagnesaemia increases the risk of torsades de pointes with a QT-prolonging drug. Correct electrolytes first and monitor the ECG.
Potassium/magnesium depletion by furosemide predisposes to ventricular arrhythmias on sotalol.
Potassium, magnesium, ECG (QT).
Syncope or ventricular tachycardia (torsades).
Correct the hypokalaemia before combining and monitor electrolytes.
DailyMed (FDA) — approved Sotalol label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9a36d95c-6e93-4e57-befe-b5274f359244 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Combining Amikacin with Furosemide increases the risk of ototoxicity and nephrotoxicity through an additive effect on the inner ear and the kidney.
Both amikacin (aminoglycoside) and furosemide (loop diuretic) are ototoxic, and the combination potentiates the risk of auditory and vestibular damage, especially in patients with renal impairment, high doses or rapid intravenous administration. The amikacin label recommends avoiding concomitant use with potent diuretics (ethacrynic acid or furosemide), because diuretics can cause ototoxicity on their own and, given intravenously, can increase aminoglycoside toxicity by altering its serum and tissue concentrations; the furosemide label states it may increase the ototoxic potential of aminoglycosides, especially with impaired renal function, and advises against the combination except in life-threatening situations. If unavoidable, monitor renal function, audiometry and signs of vestibulotoxicity (dizziness, nystagmus, tinnitus).
Amikacin + furosemide: additive ototoxicity (auditory and vestibular). Avoid the combination, except in life-threatening situations.
Amikacin (aminoglycoside) and Furosemide (loop diuretic) are both ototoxic and nephrotoxic; co-administration potentiates vestibular/cochlear and renal toxicity, especially with renal impairment or dehydration.
Monitor renal function, urine output, electrolytes and ototoxic signs; serum amikacin levels during prolonged regimens.
Tinnitus, vertigo, hearing loss or worsening renal function require prompt discontinuation and evaluation.
Avoid the combination; if needed, minimize duration, ensure adequate hydration and adjust the amikacin dose to renal function.
DailyMed/FDA (NIH/NLM) — approved Amikacin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f260ff2a-76a0-4672-9516-91c344b67890 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cdcd001-ab4b-4210-a455-2e17a7bc4972 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Combining Streptomycin (an aminoglycoside) with loop diuretics (Furosemide) raises the risk of ototoxicity and nephrotoxicity.
Streptomycin has intrinsic ototoxic potential (predominantly vestibular, with headache, nausea, vomiting and disequilibrium, and high-frequency hearing loss), and furosemide potentiates this potential. The streptomycin label explicitly states that the ototoxic effects of aminoglycosides, including streptomycin, are potentiated by co-administration of furosemide and other diuretics; the furosemide label advises against the combination with aminoglycosides, except in life-threatening situations, especially with impaired renal function. If unavoidable, monitor renal function, audiometry and vestibular signs, and adjust doses.
Streptomycin + furosemide: additive ototoxicity (vestibular and auditory). Avoid the combination, except in life-threatening situations.
Additive toxicity to the inner ear and kidney.
Hearing (tinnitus, hearing loss) and renal function (creatinine).
Tinnitus, hearing loss, dizziness; rising creatinine.
Avoid if possible; if unavoidable, reduce doses and monitor renal function and hearing.
DailyMed/FDA (NIH/NLM) — approved Streptomycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=abd1f64e-4283-4370-aae8-3666316aa36e ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cdcd001-ab4b-4210-a455-2e17a7bc4972
Combining Gentamicin with Furosemide increases the risk of ototoxicity and, to a lesser degree, nephrotoxicity, through an additive effect on the inner ear and the kidneys.
Gentamicin (aminoglycoside) is ototoxic and nephrotoxic, and furosemide increases the ototoxic potential of aminoglycosides, especially in the presence of renal impairment; the furosemide label recommends avoiding the combination except in life-threatening situations. Furosemide-induced hypovolaemia can also reduce gentamicin renal clearance and increase the risk of nephrotoxicity. If the combination is unavoidable, use the lowest effective doses, monitor renal function, aminoglycoside serum levels (when available), audiometry and vestibular signs, and maintain adequate hydration.
Furosemide + gentamicin: additive ototoxicity and nephrotoxicity. Avoid the combination, except in life-threatening situations.
Both Furosemide (loop diuretic) and Gentamicin (aminoglycoside) are ototoxic and nephrotoxic; together they exert additive toxicity on the cochlea/vestibule and the renal tubule, particularly in patients with renal impairment or volume depletion.
Monitor renal function (creatinine/clearance), urine output, electrolytes and signs of ototoxicity (tinnitus, vertigo, hearing loss). Check aminoglycoside serum levels during prolonged therapy.
Tinnitus, vertigo, hearing loss, oliguria or a rapid rise in creatinine require prompt discontinuation and evaluation.
Avoid the combination whenever possible; if unavoidable, use the shortest course and adjust doses to renal function. Consider an alternative to either drug.
DailyMed/FDA (NIH/NLM) — approved Gentamicin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=441b6232-bb60-40ad-85ec-7c41ba43fd5f ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cdcd001-ab4b-4210-a455-2e17a7bc4972 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Corticosteroid + loop diuretic: additive hypokalaemia risk.
Furosemide causes renal potassium loss and hypochloraemic alkalosis, and corticosteroids such as prednisolone increase potassium excretion (sodium and water retention, potassium loss, hypokalaemic alkalosis — listed as fluid and electrolyte disturbances in the corticosteroid labels). The combination adds up the risk of hypokalaemia, which can precipitate arrhythmias, muscle weakness and worsen heart failure control. Monitor serum electrolytes, especially potassium, and consider potassium supplementation or a potassium-sparing diuretic under guidance.
Furosemide + prednisolone: additive risk of hypokalaemia and hypokalaemic alkalosis. Monitor potassium and consider supplementation.
Both increase renal potassium loss.
Serum potassium and hypokalaemia symptoms.
Weakness, cramps, arrhythmias.
Monitor serum potassium; consider supplementation if needed.
DailyMed (FDA) — approved Prednisolone label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=52e6e21d-94b8-41a0-8d13-371c0e66bcee ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Adding acetazolamide to furosemide may deepen metabolic acidosis and hypokalaemia.
Acetazolamide (carbonic anhydrase inhibitor) promotes renal loss of bicarbonate, sodium, water and potassium, and furosemide also causes potassium loss and hypochloraemic alkalosis; the acetazolamide label contraindicates its use when serum sodium and/or potassium levels are depressed. Together, the risk of hypokalaemia, hyponatraemia and alkalosis is additive, with potential for arrhythmias, weakness and clinical worsening in patients with heart or liver failure. Monitor serum electrolytes (potassium, sodium, bicarbonate) and renal function during the combination.
Acetazolamide + furosemide: additive renal potassium loss with a risk of hypokalaemia and alkalosis. Monitor electrolytes.
Both cause bicarbonate/chloride and potassium loss; risk of marked metabolic acidosis.
Potassium, chloride, pH.
Signs of acidosis (Kussmaul breathing) or arrhythmia.
Monitor gases and electrolytes; use cautiously in the elderly.
DailyMed (FDA) — approved Acetazolamide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=268db224-d5db-457c-86bc-972c9fe07917 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
First-dose ACE-i in a patient on an active diuretic may cause hypotension.
Ramipril (ACE inhibitor) can cause symptomatic hypotension, especially after the first dose, and the risk is higher in patients with volume and/or sodium depletion from prolonged diuretic therapy (such as furosemide); the ramipril label recommends correcting volume/sodium depletion before starting the ACE inhibitor. The combination can also raise serum creatinine (especially in patients with pre-existing renal impairment or renal artery stenosis), possibly requiring dose reduction of the ACE inhibitor and/or the diuretic. Start ramipril at the lowest dose, preferably at bedtime or with the patient supine, monitor blood pressure in the first hours after the first dose, and check creatinine and potassium in the first weeks.
Furosemide + ramipril: risk of symptomatic first-dose hypotension (diuretic-induced volume depletion) and renal deterioration. Monitor blood pressure, creatinine and potassium.
Volume depletion by the diuretic amplifies first-dose ACE-i hypotension.
Blood pressure, presyncope symptoms.
Symptomatic hypotension or syncope on first dose.
Adjust the diuretic before starting the ACE-i and check blood pressure.
DailyMed (FDA) — approved Ramipril label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3806abdc-6aec-4252-bd79-e2c115b849aa ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6d9caaab-d874-4cf1-b9fe-408452a18998 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Combining Tobramycin with Furosemide increases the risk of ototoxicity and nephrotoxicity through an additive effect on the inner ear and the kidney.
Tobramycin (aminoglycoside) is ototoxic and nephrotoxic, and the tobramycin label states that aminoglycosides should not be given concurrently with potent diuretics such as ethacrynic acid and furosemide, because some diuretics cause ototoxicity on their own and intravenous diuretics can increase aminoglycoside toxicity by altering its serum and tissue concentrations. The furosemide label adds that it may increase the ototoxic potential of aminoglycosides, especially with impaired renal function, and advises against the combination except in life-threatening situations. If unavoidable, monitor renal function, aminoglycoside levels, audiometry and vestibular signs.
Furosemide + tobramycin: additive ototoxicity and nephrotoxicity. Avoid the combination, except in life-threatening situations.
Tobramycin (aminoglycoside) and Furosemide (loop diuretic) share cochlear/vestibular and renal toxicity; combined use sums these effects, with greater risk when renal function is impaired.
Monitor renal function, diuresis, electrolytes and ototoxicity signs; tobramycin serum levels when indicated.
Tinnitus, vertigo, hearing loss or worsening renal function require prompt discontinuation and reassessment.
Avoid the combination; if unavoidable, shorten the course, optimize hydration and adjust doses to renal function.
DailyMed/FDA (NIH/NLM) — approved Tobramycin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c4751a4f-c9c1-60c5-e053-2995a90aeba9 ; approved Furosemide label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7cdcd001-ab4b-4210-a455-2e17a7bc4972 — with additional reference: Prontuário Terapêutico do INFARMED, INFARMED (11th ed., 2012)
Liquorice causes potassium depletion and sodium retention, adding to the furosemide effect and increasing the risk of hypokalaemia.
Avoid excessive liquorice intake during treatment.
EMC-UK (MHRA) — approved Furosemide SmPC: https://www.medicines.org.uk/emc/product/2380/smpc
Furosemide is contraindicated in anuria because the diuretic effect depends on renal function.
Do not use in patients with anuria.
EMC-UK (MHRA) — approved Furosemide SmPC: https://www.medicines.org.uk/emc/product/2380/smpc
Furosemide crosses the placenta; data in pregnancy are limited and use should only occur if the benefit outweighs the risk.
Avoid as routine diuretic therapy in pregnancy; restrict to clear indications.
Furosemide is excreted into breast milk and may suppress lactation; consider suppressing lactation at high doses.
Diuretics are not indicated in normal pregnancy; review chronic therapy in women of childbearing age.
EMC-UK (MHRA) — approved Furosemide SmPC: https://www.medicines.org.uk/emc/product/2380/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Highly effective loop diuretic. Diuresis begins about 5 minutes after intravenous administration, with peak effect within the first half hour; the duration of the diuretic effect is approximately 2 hours.
Inhibits mainly the reabsorption of sodium and chloride in the loop of Henle (and also in the proximal and distal tubules), independently of carbonic anhydrase and aldosterone. This unique site of action accounts for its high efficacy.
Furosemide is extensively bound to plasma proteins, mainly albumin (91 to 99% at concentrations of 1 to 400 mcg/ml). Enteral bioavailability relative to the intravenous route is about 79%.
The main (or only) biotransformation pathway in man is the formation of furosemide glucuronide. A significant proportion of the dose is eliminated unchanged in the urine.
The terminal half-life is approximately 2 hours. In the elderly, albumin binding may be reduced, with lower renal clearance and a decreased initial diuretic effect.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
