Lithium's Effect on Magnesium Levels
Lithium therapy increases serum magnesium levels while potentially decreasing tissue magnesium concentrations in various organs. 1, 2
Effects of Lithium on Magnesium Homeostasis
- Lithium treatment increases plasma magnesium levels throughout the 24-hour period in patients with manic-melancholic disorder 1
- In rats, oral lithium administration increased serum magnesium concentration throughout experimental periods 2
- Despite increased serum levels, lithium can decrease magnesium concentration in tissues including liver, kidney, brain, and femoral muscle after three weeks of administration in animal models 2
- Lithium treatment results in increased urinary magnesium excretion during daytime hours 1
- Long-term lithium treatment initially produces a positive magnesium balance, but this effect diminishes with continued treatment 3
Clinical Implications and Monitoring
- Magnesium plays an important role in cardiac electrophysiology according to the American College of Cardiology, making monitoring particularly important in patients with cardiac conditions 4
- The American Heart Association suggests that magnesium has been associated with benefit in treating torsades de pointes and ventricular arrhythmias 4
- In heart failure patients, hypomagnesemia is associated with more frequent ventricular arrhythmias, and magnesium supplementation can significantly reduce premature ventricular contractions 4
- Normal serum magnesium levels are defined as ≥0.70 mmol/l by the European Society for Clinical Nutrition, with hypomagnesemia classified as:
- Mild: between 0.76 and 0.64 mmol/l
- Moderate: between 0.63 and 0.40 mmol/l
- Severe: <0.40 mmol/l 4
Special Considerations
- Patients with kidney disease require special attention since both lithium and altered magnesium levels can impact renal function 4
- The European Society for Medical Oncology emphasizes the importance of monitoring magnesium levels in cancer patients and other clinical populations 4
- Selenium co-administration may help mitigate some of lithium's effects on electrolyte balance, though this has primarily been demonstrated in animal models 5
- Lithium-induced changes in urinary magnesium excretion may be secondary to diminished renal water reabsorption rather than mediated through changes in plasma aldosterone 6
Monitoring Recommendations
- Regular monitoring of serum magnesium levels is advisable in patients on lithium therapy, especially those with cardiac conditions or renal impairment 4
- Be aware that normal serum magnesium levels may mask tissue magnesium depletion, as suggested by animal studies showing decreased tissue magnesium despite increased serum levels 2
- Consider the potential impact of lithium on calcium and phosphate metabolism as well, as lithium affects these electrolytes concurrently 3