How is Lasix (furosemide) used for diuresis?

Furosemide (Lasix) Use for Diuresis

Furosemide is a potent loop diuretic that acts on the ascending limb of the loop of Henle to inhibit active chloride reabsorption, making it highly effective for diuresis in various clinical conditions including heart failure, cirrhosis, and renal disease.

Mechanism of Action and Pharmacology

• Furosemide works at the luminal surface of the ascending limb of the loop of Henle by inhibiting the active reabsorption of chloride 1
• It has a rapid onset of action: within minutes when administered intravenously and within 1 hour when given orally 2
• Duration of action is relatively short (3-6 hours), making it suitable for rapid diuresis 2
• The drug is delivered to its site of action by active secretion via the nonspecific organic acid pump 1

Clinical Indications for Furosemide

Furosemide is indicated for:

• Edema associated with congestive heart failure
• Cirrhosis of the liver
• Renal disease, including nephrotic syndrome
• Acute pulmonary edema (particularly when rapid onset of diuresis is desired)
• Cases where greater diuretic potential is needed 3

Dosing Guidelines

Heart Failure

• Initial dose: 20-40 mg IV bolus at admission 4
• For volume overload, dose may be increased according to renal function and history of chronic diuretic use 4
• Continuous infusion may be considered after initial bolus 4
• Total dose should remain <100 mg in first 6 hours and <240 mg during first 24 hours 4
• For maintenance therapy, some patients may be controlled on as little as 20 mg daily 5

Cirrhosis with Ascites

• Initial dose: 40 mg daily, preferably used after or with spironolactone (100 mg) 2
• Maintain a 100:40 mg ratio of spironolactone:furosemide to help maintain normokalemia 2
• In children with cirrhotic ascites: 0.5 mg/kg/dose twice daily, increased as needed 4

Pediatric Dosing

• For acute diuresis: 0.5-2.0 mg/kg 2
• For cirrhotic ascites in children: 0.5-1 mg/kg/dose twice daily 4
• Maximum dose: 6 mg/kg/day for routine use, up to 10 mg/kg/day for short periods (<1 week) 2

Monitoring and Management

Parameters to Monitor

• Urine output (bladder catheter placement often desirable for close monitoring) 4
• Daily weight (maximum weight loss of 0.5 kg/day in patients without edema) 4
• Serum electrolytes (particularly potassium, sodium, magnesium) 3
• Renal function (BUN, creatinine) 3
• Blood pressure and heart rate 2

Potential Adverse Effects

• Electrolyte imbalances: hypokalemia, hyponatremia, hypochloremic alkalosis, hypomagnesemia 3
• Volume depletion and dehydration, especially in elderly patients 3
• Ototoxicity, particularly with high doses or when combined with other ototoxic drugs 3
• Hyperuricemia and potential precipitation of gout 3
• Glucose intolerance 3

Combination Therapy

• Aldosterone antagonists: Spironolactone is the mainstay of diuretic treatment in cirrhosis, with furosemide added as combination therapy 4
• Thiazides: May be useful in cases of diuretic resistance 4
• For volume-overloaded patients with heart failure, combination of hydrochlorothiazide (25 mg) and aldosterone antagonists (spironolactone 25-50 mg) with loop diuretics can be more effective 4

Special Considerations

Refractory Cases

• High-dose furosemide (≥500 mg/day) can be considered in severe cardiac failure refractory to conventional therapy 6
• Continuous infusion may be more effective than bolus dosing in some refractory cases 4

Precautions

• Discontinue if serum sodium falls below 125 mmol/L 2
• Avoid in marked hypovolemia or severe hyponatremia 2
• Use cautiously in patients with hypoproteinemia as drug effect may be weakened 3
• Avoid concomitant use with NSAIDs as they may reduce natriuretic effects 2

Optimizing Therapy

• Combine with sodium-restricted diet to enhance diuretic effect 7
• Consider twice-daily dosing rather than once-daily due to short half-life for more effective diuresis 7
• In cirrhosis, always use after or with spironolactone to maintain electrolyte balance 4
• For acute heart failure, consider combination with vasodilators for patients with SBP >110 mmHg 4

By following these guidelines for furosemide administration, clinicians can effectively manage fluid overload while minimizing adverse effects and optimizing patient outcomes.