What is the best way to correct magnesium deficiency?

Magnesium Correction: Dosing and Administration

First-Line Treatment Based on Severity

For mild hypomagnesemia (>0.5 mmol/L or >1.2 mg/dL), start with oral magnesium oxide 12-24 mmol daily, with the initial 12 mmol dose given at night when intestinal transit is slowest to maximize absorption. 1, 2

For severe or symptomatic hypomagnesemia (<0.5 mmol/L or <1.2 mg/dL), use parenteral magnesium sulfate with an initial dose of 1-2 g IV over 5-15 minutes, followed by continuous infusion if needed. 1

Specific Dosing Formulas by Clinical Scenario

Mild Hypomagnesemia (Oral Route)

• Magnesium oxide 12 mmol at night initially 1, 2
• Increase to 24 mmol daily (divided doses) if inadequate response 1, 2
• Magnesium oxide is preferred because it contains more elemental magnesium than other salts and converts to magnesium chloride in the stomach 2
• Alternative: Organic salts (aspartate, citrate, lactate) have higher bioavailability than oxide or hydroxide 2

Severe Hypomagnesemia (Parenteral Route)

FDA-approved dosing for severe deficiency: 3

• IM route: 1 g (8.12 mEq) every 6 hours for 4 doses, OR up to 250 mg/kg (approximately 2 mEq/kg) within 4 hours if necessary 3
• IV route: 5 g (approximately 40 mEq) added to 1 liter of D5W or normal saline, infused over 3 hours 3
• Maximum rate: Do not exceed 150 mg/minute (1.5 mL of 10% solution) except in life-threatening situations 3

Life-Threatening Presentations

For torsades de pointes or severe arrhythmias with prolonged QT: 1

• Give 1-2 g magnesium sulfate IV bolus over 5 minutes regardless of baseline magnesium level 1, 2
• This is indicated even if measured magnesium levels are normal 2

Critical Pre-Treatment Step

Before administering magnesium, correct water and sodium depletion with IV saline to eliminate secondary hyperaldosteronism, which increases renal magnesium wasting. 1, 2 This is particularly crucial in patients with high-output stomas, diarrhea, or gastrointestinal losses where each liter of jejunostomy fluid contains approximately 100 mmol/L sodium 1

Treatment Algorithm for Associated Electrolyte Abnormalities

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

• Hypomagnesemia causes dysfunction of potassium transport systems and increases renal potassium excretion 1
• Calcium supplementation will be ineffective until magnesium is repleted, with calcium normalization typically occurring within 24-72 hours after magnesium repletion begins 1

Monitoring Targets and Toxicity

Target serum magnesium level: >0.6 mmol/L (minimum) to 1.8-2.2 mEq/L (normal range) 2

Monitor for magnesium toxicity during IV replacement: 1

• Loss of patellar reflexes (first sign)
• Respiratory depression
• Hypotension and bradycardia
• Drowsiness and muscle weakness 2

Have calcium chloride available to reverse magnesium toxicity if needed. 1

Special Populations and Refractory Cases

Renal Insufficiency

• Maximum dose: 20 grams per 48 hours with frequent serum magnesium monitoring 1, 3
• Establish adequate renal function before administering any magnesium supplementation 4

Malabsorption/Short Bowel Syndrome

• Higher oral doses or parenteral supplementation required 1, 2
• Consider subcutaneous magnesium sulfate 4-12 mmol added to saline bags, administered 1-3 times weekly 1
• Spread supplements throughout the day to maximize absorption 2

Refractory Oral Therapy

If oral magnesium fails, add oral 1-alpha hydroxy-cholecalciferol (0.25-9.00 μg daily) in gradually increasing doses to improve magnesium balance, while monitoring serum calcium regularly to avoid hypercalcemia. 1, 2

Critical Pitfalls to Avoid

• Do not mix magnesium sulfate with calcium or vasopressors in the same IV solution 1
• Separate calcium and iron supplements from magnesium by at least 2 hours, as they inhibit each other's absorption 1
• Most magnesium salts are poorly absorbed and may worsen diarrhea or stomal output in patients with gastrointestinal disorders 1, 2
• Rapid infusion can cause hypotension and bradycardia 1
• Do not use continuous maternal magnesium sulfate in pregnancy beyond 5-7 days, as it can cause fetal abnormalities 3
• Use a central venous catheter for administration to avoid tissue injury from extravasation 1