What is the treatment for hypomagnesemia?

Treatment of Hypomagnesemia

For mild hypomagnesemia, initiate oral magnesium oxide 12-24 mmol daily (preferably at night), but only after first correcting any underlying sodium and water depletion to address secondary hyperaldosteronism. 1

Initial Assessment and Correction of Underlying Factors

Before starting magnesium supplementation, you must address the root cause of ongoing losses:

• Correct water and sodium depletion first with intravenous saline if the patient has volume depletion, as secondary hyperaldosteronism dramatically increases renal magnesium wasting and will render supplementation ineffective 2, 1
• Check renal function and avoid magnesium supplementation if creatinine clearance is <20 mL/min due to hypermagnesemia risk 1
• Measure fractional excretion of magnesium: <2% indicates gastrointestinal losses, >2% indicates renal wasting 3
• Exclude other causes in high-output stoma patients: infection, partial obstruction, medication changes 2

Oral Magnesium Therapy for Mild Hypomagnesemia

Magnesium oxide is the preferred oral formulation as it contains more elemental magnesium than other salts and is converted to magnesium chloride in the stomach 1:

• Start with 12 mmol magnesium oxide at night when intestinal transit is slowest to maximize absorption 2, 1
• Increase to 24 mmol daily if needed based on response 2, 1
• Organic magnesium salts (aspartate, citrate, lactate) have higher bioavailability than magnesium oxide and can be considered as alternatives, though they are more expensive 1, 4
• Divide doses throughout the day for continuous repletion in patients with malabsorption 1, 4

Common pitfall: Most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with gastrointestinal disorders 1

Parenteral Magnesium for Severe or Symptomatic Hypomagnesemia

For severe hypomagnesemia (<1.2 mg/dL or <0.5 mmol/L) or symptomatic patients, use parenteral magnesium 5, 3, 6:

Intravenous Administration

• Mild deficiency: 1 g (8.12 mEq) IV every 6 hours for 4 doses 5
• Severe hypomagnesemia: 5 g (approximately 40 mEq) added to 1 liter of 5% dextrose or 0.9% saline infused over 3 hours 5
• Life-threatening situations (torsades de pointes, cardiac arrhythmias): 1-2 g IV bolus over 5-15 minutes regardless of measured serum levels 2, 1, 7
• Maximum rate: 150 mg/minute except in severe eclampsia with seizures 5

Intramuscular Administration

• 2 mL of 50% solution (1 g) IM every 6 hours for 4 doses in adults 5
• For severe cases: up to 250 mg/kg (0.5 mL of 50% solution per kg) IM within 4 hours if necessary 5

Subcutaneous Administration

• 4 mmol magnesium sulfate added to saline for patients requiring supplementation 1-3 times weekly who cannot tolerate oral therapy 1, 8
• This off-label route is effective and safe for chronic management in ambulatory patients with recurrent hypomagnesemia 8

Refractory Cases and Alternative Approaches

If oral magnesium fails to normalize levels despite adequate dosing:

• Consider oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) in gradually increasing doses to improve magnesium balance 2, 1
• Monitor serum calcium regularly (every 1-2 weeks initially) to avoid hypercalcemia when using this approach 2, 1
• Reduce dietary lipids to improve magnesium absorption 1

Special Considerations

Hypokalemia with Hypomagnesemia

• Hypokalemia will be refractory to potassium supplementation until magnesium is corrected because magnesium deficiency causes dysfunction of potassium transport systems and increases renal potassium excretion 2, 1
• Normalize magnesium first, then potassium supplementation will be effective 1

Cardiac Arrhythmias

• For torsades de pointes or QTc >500 ms: Give 1-2 g IV magnesium bolus over 5 minutes regardless of baseline magnesium level 2, 1
• This is indicated even in patients without documented hypomagnesemia 2, 1

Short Bowel Syndrome/High-Output Stoma

• These patients require higher doses (12-24 mmol daily) due to significant ongoing losses 2, 1, 4
• Reduce oral hypotonic fluids to 500 mL/day—this is the most important measure 2
• Give glucose/saline solution with sodium concentration ≥90 mmol/L to sip 2
• Add loperamide 2-8 mg before food to reduce motility 2

Continuous Renal Replacement Therapy

• Use dialysis solutions containing magnesium to prevent hypomagnesemia, which occurs in up to 65% of critically ill patients on CRRT 1, 4
• This is especially important with regional citrate anticoagulation 1, 4

Monitoring

• Target serum magnesium level: >0.6 mmol/L (>1.5 mg/dL) as a reasonable minimum 1, 4
• Normal range: 1.8-2.2 mEq/L (0.74-0.91 mmol/L) 2, 3
• Monitor for signs of magnesium toxicity: hypotension, drowsiness, muscle weakness, bradycardia, respiratory depression 1
• Have calcium chloride available to reverse magnesium toxicity if needed 1