Does furosemide (Lasix) cause constipation?

Furosemide and Constipation: Clinical Evidence and Implications

Furosemide does not cause constipation; in fact, it may increase fecal water content and potentially lead to more frequent bowel movements in some patients. 1

Mechanism of Action and Effects on Bowel Function

Furosemide is a loop diuretic that acts primarily on the Na+-K+-2Cl- cotransporter (NKCC2) in the ascending limb of the loop of Henle, causing increased excretion of sodium, potassium, chloride, and water. Its effects on bowel function include:

• Increased fecal water content: Research has demonstrated that high-dose furosemide (200-800 mg daily) significantly increased fecal water content and frequency of bowel movements in patients with severe chronic renal failure 1

• Gastrointestinal fluid loss: In patients with severely impaired renal function, the gastrointestinal tract can become a major contributory site of fluid loss when on furosemide therapy 1

• Electrolyte effects: Furosemide causes increased urinary losses of multiple electrolytes, including sodium, potassium, magnesium, and zinc, which can affect fluid balance throughout the body 2

Clinical Considerations

When prescribing furosemide, be aware of the following effects that may impact bowel function:

• Volume depletion: Aggressive diuresis can lead to volume depletion, which might theoretically contribute to constipation, but this is not a direct effect of furosemide itself

• Electrolyte imbalances: Furosemide can cause electrolyte abnormalities, particularly hypokalemia, which may affect bowel motility, but this typically does not manifest as constipation 3

• Dosing considerations: Different dosing regimens of furosemide produce varying patterns of diuresis and electrolyte excretion, which could theoretically affect bowel function 4

Management Implications

When managing patients on furosemide:

1. Monitor for dehydration: Excessive fluid loss can potentially contribute to harder stools, though this is not a direct drug effect

2. Assess electrolyte balance: Regular monitoring of electrolytes is important, as imbalances can affect multiple body systems 3

3. Consider alternative causes: If constipation occurs in a patient taking furosemide, investigate other causes such as:

   • Concurrent medications (e.g., opioids)
   • Reduced physical activity
   • Inadequate fluid intake
   • Underlying gastrointestinal disorders

Common Pitfalls and Caveats

• Misattribution: Constipation occurring in patients taking furosemide is likely due to other factors rather than the medication itself

• Polypharmacy: Many patients taking furosemide have multiple comorbidities and take other medications that may cause constipation

• Fluid balance: While furosemide increases urine output, inadequate oral fluid intake to compensate for this could theoretically contribute to harder stools, but this represents dehydration rather than a direct drug effect

In conclusion, furosemide itself does not cause constipation as a direct adverse effect. If constipation occurs in patients taking furosemide, clinicians should look for alternative explanations rather than attributing it to the diuretic therapy.