Can Lasix (furosemide) cause hyponatremia?

Furosemide and Hyponatremia

Furosemide (Lasix) can cause hyponatremia, but it occurs less frequently compared to thiazide diuretics and is more likely with high doses or when combined with other medications. 1, 2

Mechanism and Risk Factors

Furosemide affects sodium levels through several mechanisms:

• Inhibits sodium reabsorption in the loop of Henle
• May cause electrolyte imbalances, including hyponatremia, especially in:
  • Patients receiving high doses (250-500 mg) 3
  • Elderly patients 1
  • Patients with heart failure 3
  • Patients with cirrhosis 4
  • Patients using alcohol 3
  • Diabetic patients 3

Evidence on Furosemide and Hyponatremia

FDA Drug Label Information

The FDA label for furosemide explicitly warns that electrolyte depletion, including hyponatremia, may occur during therapy, especially with:

• Higher doses
• Restricted salt intake
• Concomitant use of other medications 1

Clinical Studies

Recent research provides important insights:

1. Protective effect in ongoing use: A 2021 population-based case-control study found that ongoing use of furosemide was actually inversely correlated with hospitalization due to hyponatremia (aOR 0.52), suggesting a potential protective effect compared to other diuretics 2

2. Risk with new initiation: The same study showed newly initiated furosemide therapy (≤90 days) had a slightly increased risk (aOR 1.23) 2

3. Dose-dependent risk: Higher furosemide doses (250-500 mg) were independently associated with hyponatremia in heart failure patients 3

4. Combination therapy risks: Concomitant use of furosemide with spironolactone significantly increased hyponatremia risk 3

Comparison with Other Diuretics

Furosemide has a different risk profile compared to other diuretics:

• Thiazides: Cause hyponatremia in 94% of severe diuretic-induced hyponatremia cases, typically within 14 days of initiation 5
• Potassium-sparing diuretics: Spironolactone (aOR 1.96) and amiloride (aOR 1.69) have higher associations with hyponatremia than furosemide 2

Management of Diuretic-Induced Hyponatremia

If hyponatremia develops during furosemide therapy:

1. Discontinue diuretics: Guidelines recommend discontinuing diuretics and expanding plasma volume with normal saline for hypovolemic hyponatremia 4

2. Fluid restriction: Should be reserved for clinically hypervolemic patients with severe hyponatremia (serum sodium <125 mmol/L) 4

3. Hypertonic saline: Administration of 3% sodium chloride should be reserved for severely symptomatic patients with acute hyponatremia, with slow correction of serum sodium 4

4. Monitoring: Serum electrolytes should be determined frequently during the first few months of furosemide therapy and periodically thereafter 1

Clinical Pearls

• When hyponatremia develops after long-term furosemide use, consider other causes, as ongoing furosemide use is associated with lower risk of hospitalization for hyponatremia 2
• Patients with heart failure receiving both furosemide and spironolactone are at particularly high risk for hyponatremia 3
• Consider using the lowest effective dose of furosemide once the clinical condition (e.g., ascites, edema) has resolved to minimize hyponatremia risk 6
• Elderly patients, those with alcohol consumption, and diabetics require closer monitoring when on furosemide 3