Lasix - Drug Monograph

Introduction

Lasix (furosemide) is a potent loop diuretic widely used in clinical practice for its rapid and effective elimination of excess fluid from the body. First introduced in the 1960s, it remains a cornerstone therapy for managing fluid overload conditions. As a high-ceiling diuretic, furosemide produces greater diuresis than thiazide diuretics and is particularly valuable in acute care settings where prompt fluid removal is necessary.

Mechanism of Action

Furosemide acts primarily on the thick ascending limb of the loop of Henle in the nephron by competitively inhibiting the Na+/K+/2Cl- cotransporter. This inhibition reduces sodium and chloride reabsorption, creating an osmotic gradient that prevents water reabsorption. The drug also demonstrates venodilatory effects at higher doses, reducing preload in patients with congestive heart failure. Unlike thiazide diuretics, furosemide maintains efficacy even in patients with reduced renal function.

Indications

• Treatment of edema associated with congestive heart failure, cirrhosis, and renal disease
• Management of hypertension, typically as adjunctive therapy
• Treatment of acute pulmonary edema
• Forced diuresis in cases of drug overdose or toxin exposure
• Treatment of hypercalcemia (off-label)

Dosage and Administration

• Edema: 20-80 mg initially, may increase by 20-40 mg every 6-8 hours
• Hypertension: 40 mg twice daily initially, adjust based on response

• Edema: 20-40 mg IV/IM, may repeat in 1-2 hours
• Acute pulmonary edema: 40 mg IV over 1-2 minutes, may increase to 80 mg

• Renal impairment: Higher doses may be required
• Hepatic impairment: Use cautiously due to electrolyte imbalance risk
• Elderly: Start with lower doses due to increased sensitivity
• Pediatrics: 1-2 mg/kg/dose every 6-12 hours

Pharmacokinetics

Contraindications

• Anuria unresponsive to furosemide trial
• Hypersensitivity to furosemide or sulfonamide derivatives
• Hepatic coma or severe electrolyte depletion
• Concomitant use with ethacrynic acid

Warnings and Precautions

• Volume depletion: Monitor for signs of dehydration and hypotension
• Electrolyte imbalances: Risk of hypokalemia, hyponatremia, hypochloremia, hypocalcemia
• Ototoxicity: Especially with rapid IV administration, high doses, or concomitant ototoxic drugs
• Renal impairment: May require dose adjustment; monitor renal function
• Photosensitivity: Increased sensitivity to sunlight
• Systemic lupus erythematosus: May be exacerbated

Drug Interactions

• Aminoglycosides: Increased risk of ototoxicity and nephrotoxicity
• Digoxin: Hypokalemia may increase digoxin toxicity
• Lithium: Reduced renal clearance leading to lithium toxicity
• NSAIDs: Reduced diuretic and antihypertensive effects
• Probenecid: Reduces diuretic effect
• Antihypertensives: Enhanced hypotensive effect
• Corticosteroids: Enhanced potassium wasting

Adverse Effects

• Polyuria, nocturia
• Dizziness, headache
• Hyperglycemia
• Hypokalemia
• Orthostatic hypotension

• Severe dehydration
• Thrombocytopenia
• Aplastic anemia
• Stevens-Johnson syndrome
• Acute interstitial nephritis
• Pancreatitis
• Hearing loss (usually reversible)

Monitoring Parameters

• Daily weights and fluid intake/output
• Serum electrolytes (especially potassium, sodium, chloride)
• Renal function (BUN, creatinine)
• Blood pressure (standing and supine)
• Blood glucose levels
• Hearing function with high-dose or prolonged therapy
• Signs of volume depletion
• Uric acid levels (may cause hyperuricemia)

Patient Education

• Take in morning to avoid nighttime urination
• Report signs of electrolyte imbalance: muscle cramps, weakness, dizziness
• Monitor weight daily at same time with same scale
• Rise slowly from sitting/lying position to prevent dizziness
• Maintain consistent potassium intake as recommended
• Use sunscreen and protective clothing due to photosensitivity risk
• Do not skip doses without medical advice
• Report any hearing changes or ringing in ears immediately
• Regular blood tests are necessary during treatment

References

1. Goodman & Gilman's: The Pharmacological Basis of Therapeutics, 14th Edition 2. Lexicomp Online, Furosemide Monograph 3. FDA Prescribing Information for Lasix 4. KDIGO Clinical Practice Guideline for Glomerular Diseases (2021) 5. ACC/AHA/HFSA Guideline for the Management of Heart Failure (2022) 6. Chawla LS, et al. The use of diuretics in acute kidney injury. Curr Opin Crit Care. 2020 7. Ellison DH. Clinical Pharmacology in Diuretic Use. Clin J Am Soc Nephrol. 2019 8. Brater DC. Pharmacology of diuretics. Am J Med Sci. 2000