Furosemide

Furosemide is a loop diuretic approved for the following conditions across its available products and formulations:

• Edema (fluid buildup) from congestive heart failure — tablets, oral solution, and injection (IV/IM) in adults and children; Furoscix (subcutaneous) in adults and pediatric patients ≥43 kg with chronic heart failure; Lasix Onyu (subcutaneous) in adults with chronic heart failure
• Edema from cirrhosis of the liver — tablets, oral solution, and injection (IV/IM) in adults and children
• Edema from kidney disease, including nephrotic syndrome — tablets, oral solution, and injection (IV/IM) in adults and children; Furoscix (subcutaneous) in adults and pediatric patients ≥43 kg with chronic kidney disease
• High blood pressure in adults — oral furosemide (tablets and oral solution) alone or combined with other antihypertensive agents
• Acute pulmonary edema (sudden fluid in the lungs) — furosemide injection (IV), as adjunctive (add-on) therapy

Furosemide blocks the kidneys from reabsorbing sodium and chloride — especially in a key part of the kidney called the loop of Henle, but also in other tubule sections. When these salts stay in the urine instead of being pulled back into the bloodstream, water follows them out. The result is a strong, relatively fast increase in urine output that drains excess fluid from the body and helps lower blood pressure.

This mechanism is distinct from older diuretics: it works independently of the enzymes carbonic anhydrase and aldosterone, which gives furosemide its particularly strong diuretic effect compared to many other water pills.

Furosemide is taken orally (tablets or liquid) or given by injection, depending on the situation. Oral doses are typically taken once or twice daily. Injectable furosemide (IV or IM) is used in hospital settings for emergencies or when oral treatment isn't possible — the goal is always to switch back to oral therapy as soon as practical.

• Furoscix and Lasix Onyu are subcutaneous (under-skin) injections intended for short-term use — not chronic ongoing therapy
• Oral doses are adjusted individually to find the lowest dose that controls symptoms; your doctor may adjust the schedule based on your response
• Always follow your prescriber's directions; do not skip doses or change your schedule without consulting them

Furosemide commonly causes effects related to its action of removing fluid and salts from the body:

• Increased urination (this is expected and normal)
• Low potassium (hypokalemia) — muscle cramps, weakness
• Dizziness or lightheadedness, especially when standing up quickly
• Nausea, vomiting, stomach cramps, or diarrhea
• Headache
• Increased sensitivity to sunlight
• Injection or infusion site reactions (redness, bruising, pain) with injectable forms
• Elevated blood sugar or uric acid levels

Seek medical attention immediately for serious reactions like ringing in the ears or hearing loss, severe skin reactions (blistering or peeling), signs of a severe allergic reaction, or fainting — these can be signs of rare but dangerous complications.

Electrolyte and fluid loss is the most important risk. Because furosemide is a potent diuretic, too much fluid loss can cause dehydration, dangerously low blood pressure, low sodium, low potassium, and other electrolyte problems — especially in older adults and those on high doses. Your doctor will check your blood work regularly. Symptoms to watch for include extreme thirst, muscle cramps, weakness, confusion, and irregular heartbeat.

• Hearing damage (ototoxicity): Ringing in the ears or hearing loss can occur, particularly with high doses, rapid IV injection, severe kidney disease, or when combined with certain antibiotics or other ear-toxic drugs. Report any hearing changes immediately.
• Worsening kidney function: Furosemide can cause or worsen kidney problems. If urine output drops significantly during treatment, contact your doctor right away.
• Liver disease: In patients with cirrhosis, treatment should begin in a hospital; sudden fluid shifts can trigger hepatic coma.
• Urinary retention: Men with an enlarged prostate or others with bladder outflow problems may develop difficulty urinating — monitor closely at the start of treatment.

Furosemide has several important drug interactions that can cause serious harm:

• Aminoglycoside antibiotics (e.g., gentamicin, tobramycin): sharply increases risk of permanent hearing damage — avoid unless there is no alternative
• Lithium: furosemide reduces how quickly the kidneys clear lithium, raising lithium to toxic levels — avoid combining
• Ethacrynic acid: the combination raises the risk of hearing damage — avoid
• Cisplatin and other nephrotoxic drugs: increased risk of both hearing and kidney damage
• ACE inhibitors and ARBs (common heart/blood pressure medications): can cause severe low blood pressure and kidney failure — close monitoring required
• Other blood pressure medications: furosemide amplifies their blood pressure-lowering effect; doses may need adjustment
• Salicylates (high-dose aspirin): risk of salicylate toxicity due to shared kidney elimination pathways
• Indomethacin: may blunt furosemide's diuretic and blood pressure effects
• Cyclosporine: increased risk of gout due to elevated uric acid levels
• Methotrexate: furosemide may increase methotrexate toxicity by reducing its kidney clearance

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Anuria (no urine output): furosemide is contraindicated — do not use
• Allergy to furosemide or any component of the formulation: contraindicated
• Allergy to medical adhesives: the Furoscix On-body Infusor is contraindicated
• Liver cirrhosis: requires close monitoring and hospital initiation of therapy; electrolyte supplements may be needed
• Kidney disease: monitor for worsening kidney function and dehydration
• Older adults: at higher risk of dehydration, electrolyte imbalance, and dizziness/falls; kidney clearance of furosemide is reduced with age
• Urinary problems (enlarged prostate, bladder outflow obstruction): risk of acute urinary retention — careful monitoring needed
• Pregnancy: published data have not shown a clear risk of birth defects in humans, but use only if the benefit outweighs the risk; pregnant women with heart failure or cirrhosis need close monitoring
• Breastfeeding: furosemide is present in breast milk; high doses may reduce milk production — discuss the risks and benefits with your doctor
• Children: tablets, oral solution, and IV/IM injection are approved for pediatric use; the Furoscix On-body Infusor is approved for pediatric patients weighing at least 43 kg; the Furoscix ReadyFlow has not been established for pediatric use

Taking too much furosemide is essentially an extreme version of what it normally does: it can cause severe dehydration, a sharp drop in blood volume and blood pressure, and dangerous electrolyte losses — especially low potassium and low chloride. Treatment focuses on replacing lost fluids and electrolytes and closely monitoring blood pressure, electrolytes, and kidney function. Hemodialysis does not effectively remove furosemide from the body.

When furosemide is given intravenously, the diuretic effect (increased urine production) begins within about 5 minutes — slightly slower after intramuscular injection. The peak effect occurs within the first 30 minutes. The overall diuretic effect lasts approximately 2 hours after IV or IM administration.

Furosemide binds heavily to albumin (a blood protein) — between 91% and 99% of the drug in the bloodstream is protein-bound. Its half-life (the time for the body to clear half the drug) is approximately 2 hours. The body breaks furosemide down mainly into furosemide glucuronide, and most of it is removed through the kidneys in urine. More furosemide is excreted in urine after an IV injection than after an oral tablet or solution. In older adults, kidney clearance is reduced, meaning the drug may stay in the body longer.

Store at 68° to 77°F (20° to 25°C); excursions permitted to 59° to 86°F (15° to 30°C) .