Can Lasix (furosemide) cause hypokalemia and hyponatremia?

Furosemide's Effects on Electrolytes: Hypokalemia and Hyponatremia

Yes, Lasix (furosemide) can cause both hypokalemia and hyponatremia, with hypokalemia being more common and hyponatremia typically occurring with excessive or inappropriate use. 1

Mechanism of Electrolyte Disturbances

Hypokalemia

• Furosemide causes hypokalemia by inhibiting sodium and chloride reabsorption in the ascending limb of Henle's loop, leading to increased potassium excretion in the distal tubule 2
• Risk increases with higher doses (particularly >80 mg/day) 2
• Hypokalemia is a frequent accompaniment of vigorous diuretic use 3
• Hypokalemia can be particularly dangerous as it may precipitate:
  • Ventricular arrhythmias (especially in heart failure patients) 3
  • Rhabdomyolysis in severe cases 4

Hyponatremia

• Furosemide can cause hyponatremia through two primary mechanisms:
  1. Hypovolemic hyponatremia: Results from overzealous diuretic therapy causing prolonged negative sodium balance with marked loss of extracellular fluid 3
  2. Dilutional hyponatremia: Can occur in patients with impaired free water clearance (common in cirrhosis) 3

Risk Factors for Electrolyte Disturbances

• Higher doses of furosemide 2
• Concomitant use of corticosteroids, ACTH, or prolonged use of laxatives 1
• Restricted salt intake combined with high-dose diuretics 1
• Cirrhosis (particularly for hyponatremia) 3
• Female gender (diuretic-induced hyponatremia is four times more common in women) 5

Monitoring and Prevention

For Hypokalemia:

1. Monitor serum electrolytes (particularly potassium) frequently during the first few months of therapy and periodically thereafter 1
2. Consider combination therapy with aldosterone antagonists (spironolactone) in a ratio of 100:40 (spironolactone:furosemide) to maintain adequate potassium levels 2
3. Potassium chloride supplementation (20-60 mEq/day) may be required to maintain serum potassium in the 4.5-5.0 mEq/L range 3
4. Alternatively, potassium-sparing agents (amiloride, triamterene, spironolactone) can be used 3

For Hyponatremia:

1. Monitor serum sodium levels regularly 1
2. Temporarily discontinue diuretics if hyponatremia below 125 mmol/L develops 3
3. Fluid restriction (1,000-2,000 mL/day) may be valuable in patients with dilutional hyponatremia 3
4. For hypovolemic hyponatremia, management requires expansion of plasma volume with normal saline and cessation of diuretics 3

Important Clinical Distinctions

• Loop diuretics like furosemide are less likely to cause severe hyponatremia compared to thiazide diuretics 5
• In a review of 129 cases of severe diuretic-induced hyponatremia (sodium <115 mEq/L), thiazides were responsible for 94% of cases, while furosemide was rarely implicated 5
• Hyponatremia typically developed within 14 days in most patients receiving thiazides but was not observed in patients treated with furosemide alone 5
• Furosemide appears safer in patients with previous thiazide-induced hyponatremia 6

Warning Signs of Electrolyte Imbalance

Monitor for these symptoms of fluid or electrolyte imbalance 1:

• Dryness of mouth, thirst
• Weakness, lethargy, drowsiness
• Muscle pains, cramps, or fatigue
• Hypotension, oliguria
• Tachycardia, arrhythmias
• Gastrointestinal disturbances (nausea, vomiting)

When to Discontinue Furosemide

Temporarily discontinue furosemide in the following situations 3, 1:

• Severe hyponatremia (serum sodium <125 mmol/L)
• Severe hypokalemia (potassium ≤3.0 mmol/L)
• Acute kidney injury
• Hepatic encephalopathy
• Lack of response in weight with a low-salt diet

In summary, while furosemide can cause both hypokalemia and hyponatremia, hypokalemia is more common and typically requires more vigilant monitoring. Hyponatremia with furosemide is less common than with thiazide diuretics but can occur, particularly with high doses or in patients with cirrhosis or heart failure.