How to manage hyponatremia (low sodium levels) caused by diuretics?

Management of Diuretic-Induced Hyponatremia

Immediately discontinue the offending diuretic when serum sodium drops below 120-125 mmol/L, as this is the most critical first step in managing diuretic-induced hyponatremia. 1

Understanding the Problem

Diuretic-induced hyponatremia is predominantly caused by thiazide diuretics (94% of severe cases), not loop diuretics like furosemide 2. Thiazides cause hyponatremia through multiple mechanisms: they impair urinary diluting ability, stimulate vasopressin release, reduce glomerular filtration, and enhance proximal water reabsorption 3. The hyponatremia can develop extremely rapidly—within 14 days in most thiazide cases, and sometimes within just 1 day 2. Women are four times more likely to develop this complication than men 2.

Immediate Assessment

Check serum sodium, potassium, creatinine, and assess volume status clinically (looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor for hypovolemia; or edema, ascites, JVD for hypervolemia) 1, 4. Obtain urine sodium and osmolality to confirm the diagnosis 4. Most diuretic-induced hyponatremia is hypovolemic with urinary sodium typically <30 mmol/L once the diuretic effect wears off 4.

Treatment Algorithm Based on Severity

Severe Symptomatic Hyponatremia (Na <120 mmol/L with seizures, altered mental status, coma)

• Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 4, 2
• Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome 1, 4
• Monitor serum sodium every 2 hours during active correction 4
• Critical caveat: Rapid correction is particularly dangerous in diuretic-induced hyponatremia because once the diuretic is stopped and volume is repleted, the kidneys rapidly regain their ability to dilute urine, leading to inadvertent overcorrection 3

Moderate Hyponatremia (Na 120-125 mmol/L)

• Stop diuretics temporarily 1
• Administer isotonic (0.9%) saline for volume repletion if the patient is hypovolemic 4
• Implement fluid restriction to 1000-1500 mL/day if the patient is euvolemic or hypervolemic 1, 4
• Monitor serum sodium daily initially 4
• Correction rate should be 4-8 mmol/L per day, not exceeding 8 mmol/L in 24 hours 4

Mild Hyponatremia (Na 126-135 mmol/L)

• Continue diuretic therapy with close monitoring of serum electrolytes if sodium is >126 mmol/L and creatinine is normal 1, 4
• No water restriction is needed at this level 4
• Check electrolytes frequently, especially during the first month of treatment 1

Critical Management Considerations

Hypokalemia is frequently present and must be corrected, as it both contributes to the hyponatremia and increases susceptibility to osmotic demyelination syndrome 3, 2. Replacement of potassium deficits will contribute to the rise in serum sodium 3.

The maximum weight loss during diuretic therapy should be 0.5 kg/day in patients without edema and 1 kg/day in those with edema to prevent diuretic-induced complications including hyponatremia 1.

Special Populations at High Risk

Avoid thiazides entirely in:

• Frail elderly patients with chronically high water intake 3
• Patients with psychogenic polydipsia 3
• Heavy beer drinkers who depend on maximally dilute urine excretion 3
• Patients with cirrhosis who have baseline sodium <130 mmol/L 4

Prevention Strategy

Frequent measurements of serum creatinine, sodium, and potassium are essential during the first weeks of diuretic treatment, as a significant proportion of patients develop complications during this period 1. For patients with first-episode ascites, start with spironolactone monotherapy (100 mg/day) rather than combination therapy to reduce hyponatremia risk 1.

Common Pitfalls to Avoid

• Never continue thiazides when sodium drops below 120-125 mmol/L 1
• Beware of inadvertent rapid overcorrection: mortality and demyelinating syndrome are significantly associated with rapid correction exceeding 20 mEq/L in the first 24 hours 2
• Do not ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5%) and mortality (60-fold increase) 4
• Recognize that hyponatremia can develop within 1 day of thiazide initiation in susceptible patients 2