How is hypomagnesemia (low magnesium levels) treated?

Treatment of Hypomagnesemia

Intravenous magnesium sulfate is the treatment of choice for symptomatic or severe hypomagnesemia (serum Mg <0.5 mmol/L or <1.2 mg/dL), while oral magnesium supplementation is appropriate for mild, asymptomatic deficiency. 1, 2, 3

Critical First Step: Correct Underlying Fluid and Electrolyte Imbalances

Before initiating magnesium replacement, you must first correct water and sodium depletion to prevent renal magnesium wasting from secondary hyperaldosteronism. 1 This is particularly crucial in patients with high gastrointestinal losses (jejunostomy, short bowel syndrome) where hyperaldosteronism increases renal retention of sodium at the expense of magnesium and potassium. 4

• Identify and discontinue offending medications including cisplatin, cetuximab, aminoglycosides, diuretics, and proton pump inhibitors. 1
• Establish adequate renal function before administering any magnesium supplementation, as magnesium is excreted solely by the kidneys. 2, 3

Route Selection Based on Clinical Severity

Intravenous Magnesium (Symptomatic or Severe Cases)

Use IV magnesium sulfate when:

• Serum magnesium <0.5 mmol/L (<1.2 mg/dL) 1, 3
• Symptomatic hypomagnesemia (tetany, seizures, arrhythmias) regardless of level 1, 5
• Life-threatening arrhythmias (torsades de pointes) 1

Dosing for mild-to-moderate symptomatic deficiency:

• 1 g (8.12 mEq) magnesium sulfate IM every 6 hours for 4 doses (total 32.5 mEq/24 hours) 2
• Alternatively, 5 g (40 mEq) added to 1 liter of 5% dextrose or 0.9% saline for slow IV infusion over 3 hours 2

Dosing for severe hypomagnesemia:

• Up to 250 mg/kg (approximately 2 mEq/kg) IM within 4 hours if necessary 2
• IV infusion rate should generally not exceed 150 mg/minute (1.5 mL of 10% solution) 2

For life-threatening torsades de pointes:

• 1-2 g IV bolus push over 30-60 seconds 1, 2

Oral Magnesium (Asymptomatic Mild Deficiency)

Use oral magnesium when:

• Serum magnesium 0.5-0.7 mmol/L (1.2-1.7 mg/dL) and asymptomatic 1, 5
• Deficient dietary intake or malabsorption requiring prolonged therapy 5

Dosing:

• Magnesium oxide 12-24 mmol daily (typically 4 mmol capsules given at night when intestinal transit is slowest) 1
• Magnesium-containing antacids in normal dosage may be effective, though clinical proof is limited 5

Important caveat: Reduce oral magnesium dose in renal insufficiency or constipation; avoid oral antacids in hypophosphatemia. 5

Address Concurrent Electrolyte Abnormalities

Hypomagnesemia frequently coexists with hypocalcemia and hypokalemia, which will not correct until magnesium is repleted. 1, 6 This occurs because:

• Hypomagnesemia impairs parathyroid hormone release, causing calcium deficiency 4
• Hyperaldosteronism from sodium depletion increases renal potassium loss 4
• You must correct magnesium first before attempting to correct refractory hypokalemia or hypocalcemia. 6

Monitoring and Therapeutic Targets

• Effective anticonvulsant serum magnesium levels range from 2.5-7.5 mEq/L (3-9 mg/dL) 2
• Normal plasma magnesium levels are 1.5-2.5 mEq/L (1.8-3.0 mg/dL) 2
• Deep tendon reflexes decrease as plasma magnesium rises above 4 mEq/L and disappear around 10 mEq/L 2
• In severe renal insufficiency, maximum dosage is 20 grams/48 hours with frequent serum monitoring required. 2

Special Populations

Short bowel/jejunostomy patients:

• Encourage glucose-saline replacement solutions with sodium concentration ≥90 mmol/L 4
• Restrict hypotonic drinks (tea, coffee, juices) that cause sodium loss 4
• Measure 24-hour urine magnesium loss, as significant deficiency may develop despite normal serum levels 4
• Oral magnesium supplementation (often with 1-alpha calciferol) may fail, requiring IV supplementation 4

Cancer patients on chemotherapy:

• Regular monitoring is essential as cisplatin and cetuximab commonly cause significant hypomagnesemia 1

Critically ill patients on continuous kidney replacement therapy:

• Use dialysis solutions containing magnesium rather than IV supplementation, as hypomagnesemia occurs in 60-65% of these patients 1

Common Pitfalls to Avoid

• Never administer magnesium supplementation without first establishing adequate renal function, as magnesium excretion is entirely renal and toxicity can be fatal (serum levels >12 mEq/L). 2, 3
• Do not attempt to correct hypokalemia before correcting hypomagnesemia and sodium/water depletion, as hyperaldosteronism will perpetuate potassium wasting. 4
• Avoid continuous maternal magnesium sulfate administration beyond 5-7 days in pregnancy, as it can cause fetal abnormalities. 2
• Do not rely solely on serum magnesium levels in patients with gastrointestinal losses, as intracellular depletion can exist with normal serum levels. 4, 6