Can Lasix (furosemide) cause hyponatremia?

Can Lasix (Furosemide) Cause Hyponatremia?

Yes, furosemide (Lasix) can cause hyponatremia, particularly when used at high doses or in combination with other diuretics, though it is much less likely to cause hyponatremia than thiazide diuretics. 1, 2

Mechanism of Furosemide-Induced Hyponatremia

Furosemide affects sodium levels through several mechanisms:

• As a loop diuretic, furosemide primarily inhibits sodium reabsorption in the thick ascending limb of the loop of Henle
• High doses can lead to excessive diuresis, causing dehydration and electrolyte depletion 2
• The FDA label specifically lists hyponatremia as a potential adverse effect of furosemide therapy 2
• European Society of Cardiology guidelines note that high doses of diuretics may lead to hypovolemia and hyponatremia 1

Risk Factors for Furosemide-Induced Hyponatremia

Several factors increase the risk of developing hyponatremia with furosemide:

• High doses (250-500 mg) 3
• Combination with other diuretics, especially spironolactone at doses of 50-100 mg 3
• Advanced age 3
• Diabetes mellitus 3
• Alcohol consumption 3
• Restricted salt intake 2
• Cirrhosis 2
• Heart failure 1

Comparison with Thiazide Diuretics

Furosemide has a significantly lower risk of causing hyponatremia compared to thiazide diuretics:

• In a comprehensive review of 129 cases of severe diuretic-induced hyponatremia (sodium <115 mEq/L), thiazides were responsible for 94% of cases 4
• Hyponatremia typically developed within 14 days in patients receiving thiazides, but was not observed in patients treated with furosemide alone 4
• A study demonstrated that furosemide could be safely administered to an elderly woman who had previously experienced thiazide-induced hyponatremia 5

Clinical Monitoring and Management

To minimize the risk of hyponatremia with furosemide:

1. Monitor serum electrolytes (particularly sodium and potassium) frequently during the first few months of therapy and periodically thereafter 2
2. Watch for signs of fluid or electrolyte imbalance: thirst, weakness, lethargy, drowsiness, restlessness, muscle cramps, hypotension, oliguria, tachycardia, and gastrointestinal disturbances 2
3. Consider discontinuing furosemide if severe hyponatremia (serum sodium <125 mmol/L) develops 1
4. Use the lowest effective dose once ascites has resolved 1
5. Consider oral administration rather than intravenous to reduce risk of acute renal perfusion changes 6

Special Considerations

• In heart failure patients, fluid restriction to 1,000-2,000 ml/day may be valuable in patients with dilutional hyponatremia 1
• In cirrhosis patients, hyponatremia should be corrected before starting diuretic therapy 1
• Patients with hypotension (SBP <90 mmHg), severe hyponatremia, or acidosis are unlikely to respond to diuretic treatment 1

Conclusion

While furosemide can cause hyponatremia, particularly at high doses or in combination with other diuretics, it poses a significantly lower risk compared to thiazide diuretics. Careful monitoring of electrolytes and appropriate dose adjustment can minimize this risk in susceptible patients.