What is the diuretic of choice in treating hyponatremia?

Diuretic of Choice in Hyponatremia

Loop diuretics (furosemide, bumetanide, or torsemide) are the preferred diuretic class when diuresis is needed in patients with hyponatremia, as they promote free water excretion and are significantly less likely to cause or worsen hyponatremia compared to thiazide diuretics. 1

Critical First Step: Determine Volume Status

The management approach depends entirely on whether the patient has hypovolemic, euvolemic, or hypervolemic hyponatremia:

Hypovolemic Hyponatremia

• Stop all diuretics immediately and expand plasma volume with normal saline 2, 1
• This condition results from overzealous diuretic therapy causing prolonged negative sodium balance with marked extracellular fluid loss 2
• Continuing diuretics in this setting can be fatal 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Loop diuretics are the preferred agents for managing fluid retention while minimizing worsening of hyponatremia 1
• Loop diuretics inhibit sodium reabsorption at the loop of Henle, which impairs urinary concentration and allows the kidney to excrete dilute urine 1
• Thiazide diuretics should be avoided or reserved only for patients who do not respond to moderate- or high-dose loop diuretics, as they significantly worsen hyponatremia 1, 3

Euvolemic Hyponatremia (SIADH)

• Loop diuretics (20-40 mg furosemide/24 hours) combined with fluid restriction and 3% hypertonic saline for symptomatic cases 4, 5
• Vasopressin antagonists (tolvaptan) may be considered if refractory to conventional therapy 1, 6

Specific Loop Diuretic Selection

All three loop diuretics are acceptable choices, with selection based on pharmacokinetic properties 1:

• Torsemide: Longest duration of action (12-16 hours) with increased oral bioavailability 1
• Bumetanide: Increased oral bioavailability compared to furosemide (4-6 hours duration) 1
• Furosemide: Shortest duration (6-8 hours) but most widely available 1

Special Consideration: Cirrhosis with Ascites

In cirrhotic patients requiring diuresis despite hyponatremia 2:

• Start with spironolactone 100 mg daily (increasing to 400 mg/day as needed) as first-line therapy 2
• Add furosemide 40 mg daily (increasing to 160 mg/day) if suboptimal response 2
• Temporarily discontinue all diuretics if serum sodium drops below 125 mmol/L 2, 1

Critical Monitoring Parameters

• Monitor serum sodium 1-2 weeks after initiating or changing diuretic doses 1
• Avoid increasing serum sodium by >12 mEq/L per 24 hours to prevent osmotic demyelination syndrome 6, 5
• Consider discontinuing or reducing diuretic doses if serum sodium drops below 130 mmol/L 1
• In cirrhotic patients, stop diuretics if serum sodium decreases below 120 mmol/L despite water restriction 1

Common Pitfalls to Avoid

• Never continue thiazide diuretics in hyponatremic patients, as most cases of severe diuretic-induced hyponatremia are caused by thiazides rather than loop diuretics 3
• Do not use hypertonic saline in hypervolemic hyponatremia, as it worsens fluid overload 1
• Avoid fluid restriction during the first 24 hours of tolvaptan therapy if using vasopressin antagonists 6
• In susceptible patients (severe malnutrition, alcoholism, advanced liver disease), slower rates of sodium correction may be advisable 6

Adjunctive Therapies When Loop Diuretics Are Insufficient

• Tolvaptan (vasopressin V2-receptor antagonist) may be considered for hypervolemic or euvolemic hyponatremia refractory to fluid restriction and loop diuretics 1, 6
• Tolvaptan must be initiated in hospital with close sodium monitoring, starting at 15 mg daily and titrating to maximum 60 mg daily 6
• Limit tolvaptan use to 30 days maximum to minimize hepatotoxicity risk 6