What is the recommended approach for correcting magnesium deficiency (hypomagnesemia)?

Magnesium Correction

Route Selection Based on Severity

For severe or symptomatic hypomagnesemia (serum Mg <1.2 mg/dL or <0.5 mmol/L), use intravenous magnesium sulfate; for mild asymptomatic deficiency (1.2-1.7 mg/dL), oral supplementation is appropriate. 1, 2, 3

Life-Threatening Presentations

• For torsades de pointes or polymorphic ventricular tachycardia, give 1-2 g magnesium sulfate IV push over 5 minutes immediately, regardless of baseline magnesium level 2, 3, 4
• For cardiac arrest with suspected hypomagnesemia, administer 1-2 g IV push immediately 3
• For severe symptomatic hypomagnesemia with tetany or seizures, give 1-2 g IV bolus over 5-15 minutes, followed by continuous infusion 2

Severe Hypomagnesemia (Non-Life-Threatening)

• Administer 4-5 g (approximately 32-40 mEq) magnesium sulfate added to 1 liter of 5% dextrose or 0.9% saline, infused over 3 hours 4
• Alternatively, give 1 g (8.12 mEq) IM every 6 hours for 4 doses 4
• For very severe cases, up to 250 mg/kg (approximately 2 mEq/kg) may be given IM over 4 hours if necessary 4

Mild to Moderate Hypomagnesemia

• Start with oral magnesium oxide 12-24 mmol daily (approximately 480-960 mg elemental magnesium), given preferably at night when intestinal transit is slowest 1, 2, 3
• Use 4 mmol (160 mg) gelatin capsules, typically 3-6 capsules daily 1
• For general supplementation, start at the RDA: 320 mg/day for women, 420 mg/day for men 1

Critical First Step: Correct Volume Depletion

Before initiating magnesium replacement, correct water and sodium depletion with IV saline to eliminate secondary hyperaldosteronism, which causes renal magnesium wasting. 1, 2, 3

• Hyperaldosteronism from volume depletion increases renal retention of sodium at the expense of magnesium and potassium 1
• This is particularly crucial in patients with high-output stomas, diarrhea, or gastrointestinal losses 1, 2
• Failure to correct volume status first will result in continued magnesium losses despite supplementation 1

Address Concurrent Electrolyte Abnormalities

Always replace magnesium before attempting to correct hypocalcemia or hypokalemia, as these will be refractory to treatment until magnesium is normalized. 1, 2, 5

• Hypomagnesemia causes dysfunction of potassium transport systems and increases renal potassium excretion 1
• Magnesium deficiency impairs parathyroid hormone release, causing calcium deficiency 3
• Calcium normalization typically occurs within 24-72 hours after magnesium repletion begins 1

Renal Function Assessment

Check renal function before any magnesium supplementation and avoid magnesium entirely if creatinine clearance is <20 mL/min due to life-threatening hypermagnesemia risk. 1, 6

• Use extreme caution with creatinine clearance 20-30 mL/min; avoid unless life-threatening emergency 1
• Use reduced doses with close monitoring when creatinine clearance is 30-60 mL/min 1
• In severe renal insufficiency, maximum dose is 20 grams/48 hours with frequent serum monitoring 4

Monitoring Protocol

Initial Assessment (Day 0)

• Check serum magnesium, potassium, calcium, and renal function 1
• Assess for volume depletion and correct with IV saline if present 1
• Measure 24-hour urine magnesium and calculate fractional excretion if etiology unclear 6

Early Follow-Up (2-3 Weeks)

• Recheck magnesium level 2-3 weeks after starting supplementation 1
• Assess for side effects: diarrhea, abdominal distension, nausea 1
• Monitor concurrent electrolytes (potassium, calcium) 2

Maintenance Monitoring

• Check magnesium levels every 3 months once on stable dosing 1
• More frequent monitoring (every 2 weeks) if high GI losses, renal disease, or on medications affecting magnesium 1
• For cardiac emergencies, recheck within 24-48 hours after IV administration 1

Special Populations and Considerations

Short Bowel Syndrome/High GI Losses

• Require higher doses: 12-24 mmol daily (480-960 mg elemental magnesium) 1
• Administer at night when intestinal transit is slowest 1, 2
• If oral supplements fail, consider oral 1-alpha hydroxy-cholecalciferol 0.25-9.00 μg daily, monitoring calcium to avoid hypercalcemia 1, 2
• May require IV or subcutaneous magnesium sulfate (4-12 mmol added to saline bags) 1-3 times weekly 2

Continuous Renal Replacement Therapy

• Hypomagnesemia occurs in 60-65% of critically ill patients on CRRT 1, 3
• Use dialysis solutions containing magnesium to prevent ongoing losses 1, 2, 3
• Regional citrate anticoagulation increases magnesium losses through citrate-magnesium complexes 1

Post-Transplant Patients on Calcineurin Inhibitors

• Increased dietary intake alone is typically insufficient 2
• Magnesium supplements are usually necessary 2
• Monitor calcium, phosphorus, and magnesium per transplant protocols 2

Formulation Selection

Organic magnesium salts (aspartate, citrate, lactate) have better bioavailability than magnesium oxide or hydroxide for chronic oral supplementation. 1

• Liquid or dissolvable forms are better tolerated than pills 1
• Magnesium oxide causes more osmotic diarrhea due to poor absorption but may be preferred for constipation 1
• Most magnesium salts are poorly absorbed and may worsen diarrhea in patients with GI disorders 1, 2

Common Pitfalls to Avoid

• Never supplement magnesium without first checking renal function 1, 6
• Do not attempt to correct hypokalemia or hypocalcemia before normalizing magnesium 1, 2
• Do not forget to correct volume depletion first in patients with GI losses 1, 2, 3
• Avoid administering calcium and magnesium supplements together; separate by at least 2 hours 2
• Do not mix magnesium sulfate with calcium or vasoactive amines in the same IV solution 2
• Do not exceed IV infusion rate of 150 mg/minute except in severe eclampsia with seizures 4
• Avoid continuous maternal administration beyond 5-7 days in pregnancy due to fetal abnormalities 4

Signs of Magnesium Toxicity

Monitor for the following during IV replacement 2:

• Loss of patellar reflexes
• Respiratory depression
• Hypotension and bradycardia
• Have calcium chloride available to reverse toxicity if needed 2