Can I give Lasix (furosemide) to a patient with impaired renal function?

Administering Lasix in Patients with Elevated BUN and Creatinine

Furosemide should be used with caution in patients with BUN 78 and creatinine 2.26, with careful monitoring of renal function and electrolytes, but it is not absolutely contraindicated if clinically indicated for fluid overload. 1

Understanding Furosemide in Renal Impairment

Furosemide (Lasix) is a loop diuretic that acts at the loop of Henle to inhibit sodium and chloride reabsorption. In patients with impaired renal function, several important considerations apply:

• Loop diuretics maintain their efficacy unless renal function is severely impaired 2
• The pharmacokinetics of furosemide are altered in renal impairment:
  • Elimination half-life is prolonged 3
  • Drug may remain detectable in serum for up to 4 hours after administration in patients with creatinine >200 μmol/L 3
  • Higher doses may be required for the same effect as renal function declines 2

Risk Assessment for Your Patient

With a BUN of 78 and creatinine of 2.26, your patient has moderate-to-severe renal impairment. Key risks include:

1. Worsening renal function: Furosemide can lead to further deterioration in renal function, especially in the absence of peripheral edema 2
2. Electrolyte imbalances: Hypokalemia, hyponatremia, and hypochloremic alkalosis are common 1
3. Ototoxicity: Risk is increased in patients with hypoproteinemia and renal impairment 1
4. Dehydration: Can occur with excessive diuresis, potentially causing circulatory collapse 1

Decision Algorithm

1. Assess clinical necessity:

   • Is there evidence of fluid overload (peripheral edema, pulmonary congestion)?
   • Are there alternative approaches to manage the patient's condition?

2. If furosemide is deemed necessary:

   • Start with lower doses (e.g., 40mg) 3
   • Monitor response carefully
   • Adjust based on clinical response rather than automatically increasing to high doses

3. Monitoring requirements:

   • Check serum electrolytes, BUN, and creatinine frequently during the first few months of therapy 1
   • Monitor for signs of fluid/electrolyte imbalance: thirst, weakness, lethargy, muscle cramps, hypotension, tachycardia 1
   • Weight daily to assess fluid status

Practical Recommendations

• If administering furosemide, ensure adequate monitoring of renal function and electrolytes
• Consider intravenous administration if rapid diuresis is needed, as oral bioavailability may be reduced in heart failure due to gut wall edema 2
• The maximum daily dose of furosemide is 600 mg, but lower doses are advisable in renal impairment 2
• Weight loss should not exceed 0.5 kg/day in patients without peripheral edema or 1 kg/day in those with edema 2

Important Cautions

• Avoid combining with other nephrotoxic drugs when possible
• Be aware that furosemide can increase the risk of cephalosporin-induced nephrotoxicity even with minor renal impairment 1
• Reversible elevations in BUN may occur and are associated with dehydration, which should be avoided in patients with renal insufficiency 1
• Consider combination with low-dose dopamine (1 μg/kg/min) if serum creatinine is <400 μmol/L, as this may help preserve renal function 4

If the patient's condition permits, careful administration with close monitoring is reasonable, but be prepared to discontinue if renal function worsens significantly or electrolyte abnormalities become severe.