What is Furosemide?
A loop diuretic for edema (fluid retention) and hypertension, available as oral tablets and as an injectable for IV use. It blocks reabsorption of sodium, chloride, and water in the kidney, so urine output climbs and fluid overload comes down. That relieves swelling, shortness of breath, and elevated pressure.
Generic name: furosemide. Brand name: Lasix.
Drug Classification
Therapeutic class: diuretic. Pharmacologic class: loop diuretic, named for its site of action in the loop of Henle.
Indications and Therapeutic Effects
Edema from heart failure, where a failing pump backs fluid into the lungs and tissues. Hypertension as add-on therapy (not first-line; furosemide lowers volume but is usually paired with other agents). Renal impairment (acute renal failure, chronic kidney disease), to drive diuresis. Liver cirrhosis with ascites, to reduce abdominal fluid. Pulmonary edema, to clear fluid off the lungs and ease breathing.
Mechanism of Action
Furosemide blocks the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, the protein that reabsorbs sodium, chloride, and potassium. Block it and those ions leave in the urine, taking water with them. The same mechanism wastes potassium, magnesium, and calcium, which often means supplementation.
Precautions and Contraindications
Use caution with a sulfonamide allergy, impaired kidney function (may need dose adjustment), and pre-existing electrolyte imbalance (potassium, sodium, magnesium), especially in heart or liver disease. Furosemide shifts blood glucose, so diabetic regimens may need adjusting. Weigh risk versus benefit in pregnancy and breastfeeding. Flag liver disease, gout, and lupus before starting.
Contraindicated outright with sulfonamide allergy, anuria (no urine to work on, so the drug does nothing), severe electrolyte imbalance such as severely low potassium or sodium (it deepens the deficit), severe hypovolemia (it pulls volume down further), and hepatic coma.
Drug Interactions
NSAIDs (ibuprofen, naproxen) blunt the diuretic and antihypertensive effect. Furosemide speeds lithium elimination, lowering its level. Other diuretics potentiate fluid and electrolyte loss and dehydration. Corticosteroids add to potassium wasting, raising hypokalemia risk. Furosemide-driven hypokalemia raises the risk of digoxin toxicity, so watch digoxin levels.
Among natural products, licorice lowers potassium (additive hypokalemia) and St. John's Wort induces enzymes that may cut furosemide's effect. With food: grapefruit juice can raise furosemide levels (avoid it), and high-salt meals work directly against the drug, so the low-salt diet stays in place.
Adverse Effects
Common: increased urination (expected), electrolyte imbalances (hypokalemia, hyponatremia, hypomagnesemia, showing as cramps, weakness, irregular heartbeat, fatigue), dizziness and lightheadedness on standing, low blood pressure, and headache.
Serious: allergic reactions (rash, itching, swelling, severe dizziness, trouble breathing). Ototoxicity, the reaction that defines IV furosemide, primarily from high doses or rapid IV push and more likely with renal impairment or concurrent aminoglycosides, causing hearing loss or tinnitus, so report any hearing change immediately (Furosemide, StatPearls). Hypersensitivity reactions (fever, rash, joint pain, malaise). Pancreatitis (severe abdominal pain, nausea, vomiting). Erythema multiforme (target or "bull's eye" lesions). Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), with rapidly spreading rash, blistering or peeling skin, and mucous membrane involvement. Rarely, aplastic anemia and agranulocytosis.
Administration Considerations
Available Forms
- Tablets: 20 mg, 40 mg, 80 mg, 500 mg.
- Oral solution: 8 mg/mL (pineapple, peach flavor), 10 mg/mL (orange flavor).
- Solution for injection: 10 mg/mL.
Dosage for Neonates
Edema
- PO (Neonates): 1-4 mg/kg/dose 1-2 times/day.
- IM, IV (Neonates): 1-2 mg/kg/dose q 12-24 hr.
Dosage for Children
See also: Pediatric Dosage Calculations
Edema
- PO (Children >1 mo): 2 mg/kg as a single dose; may increase by 1-2 mg/kg q 6-8 hr (maximum dose = 6 mg/kg).
- IM, IV (Children): 1-2 mg/kg/dose q 6-12 hr; continuous infusion, 0.05 mg/kg/hr, titrate to clinical effect.
Dosage for Adults
Edema
- PO (Adults): 20-80 mg/day as a single dose initially, may repeat in 6-8 hr; may increase by 20-40 mg q 6-8 hr until desired response. Maintenance once or twice daily (doses up to 2.5 g/day have been used in HF or renal disease). Hypercalcemia, 120 mg/day in 1-3 doses.
- IM, IV (Adults): 20-40 mg, may repeat in 1-2 hr and increase by 20 mg every 1-2 hr until response; maintenance q 6-12 hr. Continuous infusion, bolus 0.1 mg/kg followed by 0.1 mg/kg/hr, double q 2 hr to a maximum of 0.4 mg/kg/hr.
Hypertension
- PO (Adults): 40 twice daily initially (when added to a regimen, decrease the dose of other antihypertensives by 50%); adjust further dosing based on response.
Pharmacokinetics
Absorption: well absorbed orally, roughly 60-70% reaching circulation; onset within one hour, peak at 1-2 hours. Distribution: large volume of distribution; crosses the placenta and enters breast milk. Protein binding: about 91-99%, mainly to albumin. Metabolism: minimal hepatic (less than 10%), most of the drug excreted unchanged. Elimination: renal, via glomerular filtration and tubular secretion. Half-life: short, 30-60 minutes with normal renal function, prolonged with renal impairment. Adjust against creatinine clearance or eGFR, and review the med list for agents affecting renal function or electrolytes before starting.
Nursing Considerations for Furosemide
Nursing Assessment
Take a full history first: allergies, kidney and liver function, cardiac status, electrolyte problems, and current meds. These drive contraindications and interactions. Monitor blood pressure, heart rate, and respiratory rate, since the whole point of the drug is to drop volume and that moves the vitals. Track fluid balance closely (intake and output, daily weights, signs of overload or dehydration); daily weight is the most reliable read on whether the drug is working. Watch electrolytes, particularly potassium, sodium, and magnesium, since deficits show up as arrhythmias or muscle weakness. Check renal function (serum creatinine, eGFR), because worsening function raises adverse-effect risk. Watch for allergic reactions, hearing changes or tinnitus, and severe skin reactions (blistering, peeling).
Nursing Interventions
Give furosemide as prescribed (right dose, route, timing). Document intake and output and daily weights, and assess for overload or dehydration to gauge response. Monitor blood pressure for the hypotension the drug can cause. Reinforce a low-sodium diet, since high sodium drives the fluid retention you are fighting. Note and report any adverse reaction (allergy, ototoxicity, severe skin reactions) early. Coordinate with the physician, pharmacist, and dietitian, since these patients usually carry complex heart, kidney, or liver disease.
Patient Education and Teaching
Explain that furosemide clears excess fluid and eases edema and shortness of breath. Give clear dose, frequency, and timing instructions, and stress keeping the schedule. Name the common side effects (increased urination, electrolyte imbalance, dizziness, headache) so they report concerns early. Reinforce the low-sodium diet and the value of monitoring intake and output against dehydration. Set expectations for ongoing monitoring (blood pressure checks, electrolyte and renal labs, followup appointments). Have them disclose every medication, including over-the-counter products, supplements, and herbals. Cover safety: rise slowly to limit dizziness, avoid excessive sun exposure, and recognize rash or trouble breathing. Tell them to seek immediate care for severe allergic reactions, hearing changes, or skin reactions.
Evaluation and Desired Outcomes
Effective diuresis with reduced edema and easier breathing. Balanced fluid status, neither overloaded nor dehydrated, with stable weights. Blood pressure at the provider's target. Improved symptoms (less dyspnea, swelling, and fatigue) with better exercise tolerance. Stable electrolytes, particularly potassium, sodium, and magnesium. Consistent adherence to the regimen.
Frequently Asked Questions
Why does furosemide require close potassium monitoring? It blocks the Na-K-2Cl cotransporter in the loop of Henle, so potassium leaves in the urine along with sodium and water. Hypokalemia is the most common severe side effect and can trigger dangerous arrhythmias, which is why serum potassium and supplementation stay on your radar (Furosemide, StatPearls).
What is the most reliable sign the drug is working? The daily weight. Intake and output help, but a consistent morning weight on the same scale is the cleanest read on whether you are pulling off fluid or risking dehydration.
Why is IV furosemide given slowly? Rapid IV push and high doses raise the risk of ototoxicity, meaning hearing loss or tinnitus. The risk climbs further in renal impairment or when the patient is also on aminoglycosides, so push it slowly and report any hearing change.
Can a patient with a sulfa allergy take furosemide? Use caution. Furosemide is a sulfonamide derivative, so a documented sulfonamide allergy is a flagged precaution and a true allergy is a contraindication. Confirm the allergy history before giving it.
Why give the dose in the morning? Furosemide drives several hours of brisk urination after a dose. Morning dosing keeps the patient from being up overnight and supports adherence.
How is furosemide different from a thiazide diuretic? Furosemide is a high-ceiling loop diuretic that still works at low kidney function and pulls off large volumes fast. Thiazides are weaker and lose effect as renal function declines, so loop agents are preferred when rapid or higher-volume diuresis is needed.