In a stable adult with SIADH, is furosemide (Lasix) appropriate as treatment?

Furosemide is NOT Appropriate as First-Line Treatment for SIADH

Furosemide should not be used as monotherapy or routine treatment for stable SIADH, as the highest quality randomized controlled trial demonstrated no benefit over fluid restriction alone, with increased risks of acute kidney injury and hypokalemia. 1

Evidence Against Furosemide Use

The 2020 EFFUSE-FLUID trial—the only randomized controlled study specifically testing furosemide in SIADH—provides definitive evidence against its routine use 1:

• No efficacy advantage: Furosemide (20-40 mg/day) combined with fluid restriction showed no significant difference in sodium correction compared to fluid restriction alone at days 4,7,14, or 28 1
• Increased complications: Acute kidney injury and severe hypokalemia (K+ ≤3.0 mmol/L) occurred more frequently in patients receiving furosemide 1
• Equal outcomes: All three treatment arms (fluid restriction alone, fluid restriction + furosemide, and fluid restriction + furosemide + salt) achieved similar mean sodium increases of 5 mmol/L by day 4 1

Guideline-Recommended Treatment Algorithm for Stable SIADH

First-Line Treatment: Fluid Restriction

Fluid restriction to 1 L/day is the established first-line therapy for mild-to-moderate asymptomatic SIADH 2, 3:

• Target correction rate: 4-6 mmol/L per day 3
• Adjust restriction based on urine-to-serum electrolyte ratio (stricter restriction to <500 mL/day if ratio indicates need) 1
• Monitor serum sodium every 4-6 hours initially 3

Second-Line Options When Fluid Restriction Fails

Approximately half of SIADH patients do not respond adequately to fluid restriction 4. When fluid restriction is ineffective or poorly tolerated, the evidence supports these alternatives 2, 5:

1. Demeclocycline: Recommended as second-line therapy by the American College of Physicians, inducing nephrogenic diabetes insipidus 2, 6

2. Oral urea: Considered very effective and safe in recent literature 2, 4

3. Vasopressin receptor antagonists (vaptans): Tolvaptan (starting dose 15 mg once daily) is FDA-approved for clinically significant euvolemic hyponatremia 2, 5

Historical Context of Furosemide Use

Older literature from 1987 mentioned furosemide combined with 3% hypertonic saline for acute symptomatic SIADH requiring immediate intervention 6. However, this approach:

• Was intended only for emergency situations with severe symptoms (seizures, coma) 6
• Has been superseded by current guidelines recommending 3% hypertonic saline alone for severe symptomatic cases 2, 3
• Is distinct from the question of using furosemide in stable SIADH patients

Critical Pitfalls to Avoid

• Do not use furosemide as routine therapy: The 2020 RCT definitively shows no benefit and increased harm 1
• Do not confuse SIADH with cerebral salt wasting (CSW): These require opposite treatments—fluid restriction worsens CSW 2
• Never exceed 8 mmol/L sodium correction in 24 hours: Risk of osmotic demyelination syndrome 2, 3
• Monitor for overcorrection: Check sodium every 2 hours initially in severe cases, every 4-6 hours after stabilization 3

When Diuretics Might Be Considered

The only scenario where loop diuretics have limited supporting evidence is in acute severe symptomatic hyponatremia requiring emergency correction, combined with hypertonic saline 6, 7. However, even in this context, modern algorithms emphasize hypertonic saline as the primary intervention 2, 3.

For your stable adult patient with SIADH: Start with fluid restriction to 1 L/day, and if ineffective after several days, consider demeclocycline, urea, or tolvaptan—not furosemide. 2, 1, 4