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Furosemide

Furosemide

Lasix Frusid Diumide-K Frumex Fusid

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Updated: December 06, 2025

Overview

Furosemide is a potent loop diuretic that has been widely used in clinical practice since the 1960s. It is primarily employed to eliminate excess fluid accumulation in various clinical conditions by increasing urine output. As one of the most effective diuretics available, it plays a crucial role in managing fluid overload states and hypertension. The drug works by inhibiting electrolyte reabsorption in the kidneys' loop of Henle, making it particularly valuable in treating edema associated with heart failure, liver cirrhosis, and renal disease. Its rapid onset of action makes it suitable for both chronic management and acute emergency situations.

Drug Class

Loop diuretic (sulfonamide derivative) Therapeutic category: Antihypertensive, Diuretic

Mechanism of Action

Competitively inhibits the Na-K-2Cl symporter in the thick ascending limb of the loop of Henle Blocks chloride binding site on the cotransporter Results in: • Increased excretion of sodium (Na+) • Increased excretion of chloride (Cl-) • Increased excretion of potassium (K+) • Secondary increase in water excretion

Pharmacokinetics

Absorption: Variable oral bioavailability (60-64%), food delays absorption Distribution: Protein binding 91-99%, Vd 0.1-0.2 L/kg Metabolism: Hepatic glucuronidation (minor pathway) Excretion: Primarily renal (60-70% as unchanged drug), biliary (30-40%) Half-life: Normal renal function: 1.5-2 hours End-stage renal disease: 9 hours

Pharmacodynamics

Primary effects: • Rapid reduction in extracellular fluid volume • Decreased blood pressure • Increased urinary output within 20-60 minutes (PO) Secondary effects: • Activation of renin-angiotensin-aldosterone system • Electrolyte disturbances (hypokalemia, hyponatremia) • Metabolic alkalosis

Indications

• Edema associated with congestive heart failure, cirrhosis, and renal disease • Hypertension (usually as adjunct therapy) • Acute pulmonary edema • Hypercalcemia • Forced diuresis in acute drug intoxications

Contraindications

Absolute: • Anuria unresponsive to trial dose • Hypersensitivity to sulfonamides • Hepatic coma Relative: • Electrolyte depletion • Severe renal impairment • Gout • Diabetes mellitus

Dosage & Administration

Edema in adults: 20-80 mg PO/IV initially, may repeat in 6-8 hours Hypertension: 40 mg PO twice daily, adjust based on response Acute pulmonary edema: 40 mg IV, may repeat with 80 mg after 1 hour Pediatric diuresis: 1-2 mg/kg/dose every 6-12 hours Chronic renal failure: May require higher doses up to 600 mg/day

Special Populations

Pediatric: Safety established for infants >1 month, monitor growth Geriatric: Increased sensitivity, start with lower doses Renal impairment: May require higher doses but monitor closely Hepatic impairment: Increased risk of encephalopathy, use cautiously

Adverse Effects

Common (>10%): • Hypokalemia (may cause muscle weakness/cramps) • Dehydration/dizziness • Hyperglycemia • Hyperuricemia Serious (<1%): • Ototoxicity (usually with rapid IV administration) • Stevens-Johnson syndrome • Thrombocytopenia • Pancreatitis

Drug Interactions

• Aminoglycosides: Increased risk of ototoxicity • NSAIDs: Reduced diuretic effect • Digoxin: Hypokalemia increases digoxin toxicity • Lithium: Reduced renal clearance of lithium • Probenecid: Reduces diuretic effect

Warnings & Precautions

• Risk of severe fluid/electrolyte depletion (Black Box Warning) • Ototoxicity potential (especially with rapid IV administration) • May precipitate diabetes mellitus • Photosensitivity reactions possible • Monitor for gout attacks

Pregnancy & Lactation

Pregnancy: Category C - Use only if potential benefit justifies risk May affect fetal electrolyte balance/urine output Lactation: Excreted in breast milk - consider alternative or monitor infant

Monitoring Parameters

• Serum electrolytes (especially K+, Na+, Cl-) • Renal function tests (BUN, creatinine) • Blood pressure and weight • Urine output • Hearing assessments with high-dose/long-term use

Patient Counseling

• Take in morning to avoid nocturia • Report dizziness, muscle cramps, or hearing changes • Maintain adequate potassium intake • Rise slowly from sitting/lying position • Use sunscreen due to photosensitivity risk

Storage & Stability

Store at 20-25°C (68-77°F) Protect from light Keep tablets in original container IV solution stable for 24 hours at room temperature

Clinical Pearls

• IV dose is approximately half the equivalent oral dose • Hypokalemia is most common with long-term use - monitor regularly • Effect enhanced by concurrent thiazide use (sequential nephron blockade) • Assess volume status before administration • Consider potassium-sparing diuretic for chronic therapy

References

• Goodman & Gilman's: The Pharmacological Basis of Therapeutics, 14th ed • UpToDate: Furosemide drug information • RxList: Lasix (furosemide) monograph • AHFS Drug Information 2023