What are the necessary precautions and potential adverse effects when administering Furosemide (Lasix) infusion, especially in patients with impaired renal function?

Furosemide Infusion: Critical Precautions and Adverse Effects

Absolute Contraindications Before Administration

Furosemide must never be administered in patients with anuria, marked hypovolemia, severe hyponatremia (sodium <120-125 mEq/L), or systolic blood pressure <90-100 mmHg without circulatory support. 1, 2

• Anuria represents an absolute contraindication—furosemide cannot work without functioning nephrons and will only cause further deterioration 1, 3
• Severe hypovolemia will be worsened by diuresis, precipitating hypotension and organ hypoperfusion 1, 2
• Hypotension (SBP <90-100 mmHg) requires circulatory support (inotropes, vasopressors, or intra-aortic balloon pump) before or concurrent with furosemide—never give furosemide expecting it to improve hemodynamics 1, 2

Critical Precautions in Renal Impairment

In patients with impaired renal function, furosemide remains effective but requires higher doses to achieve therapeutic tubular concentrations—do not reduce the dose based on elevated creatinine alone. 1

• Loop diuretics remain the preferred class when creatinine clearance is <40 mL/min, unlike thiazides which lose effectiveness 1
• Higher doses (not lower) are required in renal impairment due to reduced tubular secretion and fewer functional nephrons 1, 2
• Furosemide should not be used to prevent or treat acute kidney injury itself—only to manage volume overload that complicates AKI 1
• High-dose furosemide (>60-80 mg) increases nephrotoxicity risk, with creatinine increases >0.3 mg/dL associated with nearly 3-fold higher in-hospital mortality 1

Administration Rate and Ototoxicity Prevention

Furosemide infusions must be administered over 5-30 minutes to prevent irreversible ototoxicity, with maximum infusion rates not exceeding 4 mg/min. 1, 2

• Rapid IV push administration, especially at high doses, causes permanent hearing loss 1, 2
• Doses ≥250 mg must be given by infusion over 4 hours 2
• Ototoxicity risk is dramatically increased when furosemide is combined with aminoglycosides, cisplatin, or ethacrynic acid—avoid these combinations except in life-threatening situations 3

Mandatory Monitoring Requirements

Check electrolytes (sodium, potassium, magnesium), creatinine, and BUN frequently during the first few months, then periodically thereafter. 3

• During initial titration: Check electrolytes and renal function every 3-7 days 1, 2
• During active diuresis: Monitor daily weights (target 0.5-1.0 kg/day loss), urine output, blood pressure 1, 2
• In acute settings: Place bladder catheter to assess hourly urine output and treatment response 2
• Hypokalemia is the most common electrolyte disturbance—temporarily suspend furosemide if potassium <3.0 mEq/L 1, 3

Dangerous Drug Interactions

Furosemide combined with ACE inhibitors or ARBs can cause severe hypotension and acute renal failure—an interruption or dose reduction may be necessary. 3

• Lithium toxicity: Diuretics reduce lithium clearance—lithium generally should not be given with furosemide 3
• NSAIDs (including indomethacin) reduce natriuretic and antihypertensive effects by inhibiting prostaglandin synthesis 3
• Nephrotoxic drugs (cisplatin, aminoglycosides, cephalosporins, cyclosporine) have enhanced toxicity when combined with furosemide 3
• Salicylates: High-dose aspirin with furosemide causes salicylate toxicity at lower doses due to competitive renal excretion 3

Metabolic and Electrolyte Adverse Effects

Hypokalemia, hyponatremia, hypomagnesemia, hypocalcemia, and metabolic alkalosis are expected complications requiring aggressive monitoring and replacement. 1, 3

• Hypokalemia: Most common—combine with spironolactone or potassium supplements 1, 3
• Hyponatremia: Stop furosemide if sodium drops <120-125 mEq/L 1, 2
• Hypocalcemia: Rare cases of tetany reported—monitor calcium levels periodically 3
• Hypomagnesemia: Often overlooked but clinically significant—check magnesium levels regularly 3
• Asymptomatic hyperuricemia is common; gout may rarely be precipitated 3

Special Population Precautions

In patients with cirrhosis and ascites, oral administration is strongly preferred over IV to avoid acute GFR reduction, with maximum dose 160 mg/day combined with spironolactone. 1, 2

• Exceeding 160 mg/day in cirrhosis indicates diuretic resistance requiring large-volume paracentesis, not further dose escalation 1, 2
• In premature infants: Furosemide may precipitate nephrocalcinosis/nephrolithiasis—monitor renal function and perform renal ultrasonography 3
• In elderly patients: Start at low end of dosing range due to decreased renal function—this drug is substantially excreted by the kidney 3
• In pregnancy: Use only if potential benefit justifies fetal risk—causes unexplained maternal deaths and abortions in animal studies 3

Volume Depletion Warning Signs

Monitor for hypovolemia: orthostatic hypotension, tachycardia, decreased skin turgor, BUN/creatinine ratio >30, and symptomatic hypotension. 1, 2

• Excessive diuresis causes intravascular volume depletion, paradoxically worsening renal perfusion 1
• Maximum safe weight loss is 0.5 kg/day without peripheral edema, 1.0 kg/day with edema 1, 2
• Dehydration should be avoided, particularly in patients with renal insufficiency—reversible BUN elevations indicate this complication 3

Diuretic Resistance Management

When standard doses fail, add a second diuretic class (thiazide or aldosterone antagonist) rather than escalating furosemide beyond 160-240 mg/day. 1, 2

• Sequential nephron blockade (combination therapy) is more effective than monotherapy escalation 1, 2
• Consider hydrochlorothiazide 25 mg or spironolactone 25-50 mg for synergistic effect 1, 2
• Continuous infusion may be superior to bolus dosing in refractory cases 2, 4

Critical Clinical Pitfalls to Avoid

Never discontinue furosemide prematurely due to modest creatinine increases if volume overload persists—worsening renal function during successful decongestion has better outcomes than failure to decongest with stable creatinine. 1

• Premature discontinuation due to azotemia is a dangerous error leading to persistent congestion 1
• Continue diuretics when clinical signs of congestion persist (JVD, peripheral edema ≥2+, pulmonary crackles, CVP >8 mmHg) 1
• Do not use furosemide in sepsis unless hypervolemia, hyperkalemia, or renal acidosis are present—it may worsen outcomes 1

Rare but Serious Adverse Effects

• Ototoxicity: Permanent hearing loss with rapid administration or high doses 1, 2, 3
• Bullous dermatosis: Photosensitivity reactions after sun exposure 3, 5
• Systemic lupus erythematosus: Possible exacerbation or activation 3
• Blood dyscrasias: Rare but requires regular monitoring 3
• Acute urinary retention: In patients with prostatic hyperplasia or urethral narrowing due to increased urine production 3