What is the recommended intravenous (IV) regimen for correcting magnesium deficiency?

Intravenous Magnesium Correction

For mild magnesium deficiency, administer 1 g (8.12 mEq) magnesium sulfate IV or IM every 6 hours for four doses; for severe hypomagnesemia, give up to 250 mg/kg (approximately 2 mEq/kg) IM over 4 hours, or alternatively 5 g (40 mEq) added to 1 liter of IV fluid infused over 3 hours. 1

Dosing Regimens by Severity

Mild Magnesium Deficiency

• Standard dose: 1 g magnesium sulfate (equivalent to 8.12 mEq) injected IM every 6 hours for 4 doses (total 32.5 mEq per 24 hours) 1
• This provides adequate repletion without exceeding renal excretory capacity 1

Severe Hypomagnesemia

Two acceptable approaches:

• Intramuscular route: Up to 250 mg/kg body weight (approximately 2 mEq/kg) given IM within a 4-hour period if necessary 1
• Intravenous infusion: 5 g (approximately 40 mEq) added to 1 liter of 5% dextrose or 0.9% sodium chloride, infused slowly over 3 hours 1

Maintenance Dosing

• To maintain serum magnesium >2.0 mg/dL: Expect to administer 2 g IV magnesium sulfate at least twice daily, as the average total serum magnesium drops below 2.0 mg/dL within 12-24 hours after a single dose 2
• In total parenteral nutrition: Maintenance requirements range from 8-24 mEq (1-3 g) daily for adults 1

Administration Guidelines

Rate of Administration

• General IV injection: Should not exceed 150 mg/minute (1.5 mL of 10% concentration) 1
• For acute severe deficiency or cardiac emergencies: May give 1-2 g IV over 5-15 minutes 1, 3
• Standard infusion protocol: Initial bolus of 8-16 mmol over 5 minutes, followed by continuous infusion of 2-4 mmol/hour to maintain plasma magnesium between 1.5-3 mmol/L 3

Concentration Requirements

• IV infusions must be diluted to ≤20% concentration prior to administration 1
• IM injections: Undiluted 50% solution is appropriate for adults, but should be diluted to ≤20% for children 1
• Common diluents include 5% dextrose or 0.9% sodium chloride 1

Special Clinical Scenarios

Cardiac Arrhythmias (Torsades de Pointes)

• For recurrent torsades de pointes with acquired QT prolongation: Administer IV magnesium sulfate regardless of baseline magnesium level 4
• Target: Replete magnesium to ≥2.0 mmol/L (or ≥2.0 mg/dL) as an anti-torsadogenic measure 4, 5
• Dosing: 1-2 g IV bolus, with increasing heart rate via pacing or isoproterenol if magnesium alone is insufficient 4

Acute Myocardial Infarction

• After the first 24 hours: Magnesium sulfate should be given as needed to replete magnesium deficits for 24 hours 4
• This recommendation applies to patients hospitalized with acute MI regardless of reperfusion therapy 4

High-Output Stoma or Short Bowel Syndrome

• Critical first step: Correct sodium and water depletion with IV saline to address secondary hyperaldosteronism before magnesium supplementation 5
• Hyperaldosteronism increases renal magnesium wasting, making supplementation ineffective until volume status is corrected 5
• After rehydration: Administer 12-24 mmol magnesium daily, preferably at night when intestinal transit is slowest 5
• For refractory cases: Consider subcutaneous magnesium sulfate (4 mmol added to saline bags) for home-based intermittent administration 5, 6

Continuous Renal Replacement Therapy (CRRT)

• Prevention strategy: Use dialysis solutions containing magnesium to prevent hypomagnesemia, which occurs in 60-65% of critically ill patients on CRRT 4, 5
• This is particularly important when regional citrate anticoagulation is used, as citrate chelates ionized magnesium 4

Critical Safety Considerations

Renal Function Assessment

• Absolute contraindication: Creatinine clearance <20 mL/min due to inability to excrete excess magnesium and risk of life-threatening hypermagnesemia 5
• In severe renal insufficiency: Maximum dosage is 20 g per 48 hours with frequent serum magnesium monitoring 1
• Always check renal function before initiating magnesium supplementation 5

Monitoring Requirements

• During infusion: Monitor for signs of magnesium toxicity including hypotension, bradycardia, respiratory depression, and loss of deep tendon reflexes 5
• Target therapeutic level: 6 mg/100 mL (2.5 mmol/L) is considered optimal for seizure control 1
• Have calcium chloride immediately available to reverse magnesium toxicity if needed 5

Duration Limitations

• In pregnancy: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities 1
• This applies to management of pre-eclampsia/eclampsia where magnesium is used for seizure prophylaxis 1

Common Pitfalls to Avoid

Failure to Address Underlying Causes

• Do not supplement magnesium without first correcting volume depletion in patients with diarrhea, high-output stomas, or secondary hyperaldosteronism 5
• Ongoing aldosterone secretion will cause continued renal magnesium wasting that exceeds supplementation 5

Concurrent Hypokalemia

• Magnesium deficiency causes refractory hypokalemia through dysfunction of multiple potassium transport systems 5
• Hypokalemia will not respond to potassium supplementation until magnesium is normalized 5
• Always check and correct magnesium when treating resistant hypokalemia 5

Inadequate Dosing Frequency

• Single daily dosing is insufficient to maintain therapeutic levels in most patients 2
• The average total serum magnesium drops below 2.0 mg/dL within 12 hours of a 2 g dose 2
• Plan for twice-daily or continuous infusion when sustained levels are required 2

Serum Levels Don't Reflect Total Body Stores

• Serum magnesium represents <1% of total body magnesium and does not accurately reflect tissue stores 5
• A normal serum level does not exclude significant total body deficiency 5
• Consider magnesium loading test (30 mmol IV over 8 hours with 24-hour urine collection) to diagnose true deficiency when clinical suspicion is high 7