What are the major interactions between lithium and furosemide (Lasix)?

From the FDA Drug Label

Lithium may prolong the effects of neuromuscular blocking agents. Therefore, neuromuscular blocking agents should be given with caution to patients receiving lithium Caution should be used when lithium and diuretics or angiotensin converting enzyme (ACE) inhibitors are used concomitantly because sodium loss may reduce the renal clearance of lithium and increase serum lithium levels with risk of lithium toxicity. Furosemide tablets combined with angiotensin converting enzyme inhibitors or angiotensin II receptor blockers may lead to severe hypotension and deterioration in renal function, including renal failure. Lithium generally should not be given with diuretics because they reduce lithium’s renal clearance and add a high risk of lithium toxicity

• Major Interactions: The use of lithium and furosemide together may lead to:
  • Reduced renal clearance of lithium
  • Increased risk of lithium toxicity
  • Severe hypotension
  • Deterioration in renal function, including renal failure 1 2

From the Research

The concurrent use of lithium and furosemide can lead to potentially serious interactions that require careful monitoring, as furosemide can significantly increase lithium levels in the blood by reducing lithium clearance through the kidneys, which may result in lithium toxicity. This interaction typically occurs because furosemide decreases sodium reabsorption in the kidneys, and since lithium follows similar reabsorption pathways as sodium, this leads to increased lithium retention. Symptoms of lithium toxicity include tremor, confusion, drowsiness, muscle weakness, vomiting, and in severe cases, seizures or coma. If these medications must be used together, lithium levels should be closely monitored, especially when furosemide is started, stopped, or has its dosage changed, as suggested by studies on lithium toxicity and its management 3, 4.

Key Considerations

• Lithium dosage may need to be reduced by approximately 25-50% when used with furosemide to prevent toxicity.
• Patients should maintain consistent sodium intake and adequate hydration to help stabilize lithium levels.
• Healthcare providers should educate patients about the signs of lithium toxicity and instruct them to seek immediate medical attention if these symptoms develop.
• The risk of lithium toxicity remains a concern when prescribing lithium, but with proper management, it can be safely used in patients who benefit from it 3.

Management Strategies

• Close monitoring of lithium levels is crucial when furosemide is initiated, changed, or discontinued.
• Patients should be aware of the signs of lithium toxicity and know when to seek medical help.
• Management of lithium side effects and toxicity involves a simple set of strategies, including minimizing lithium levels within the therapeutic range and, in some situations, prescribing side effect antidotes 4.
• Regular monitoring of renal function, thyroid function, and parathyroid function is necessary due to the potential adverse effects of lithium on these organs 4.