What is the recommended intravenous (IV) magnesium dosage for treating hypomagnesemia?

IV Magnesium Dosage for Hypomagnesemia

For mild hypomagnesemia, administer 1 g magnesium sulfate (equivalent to 8.12 mEq) IV or IM every 6 hours for four doses, while for severe hypomagnesemia (<1.2 mg/dL or <0.5 mmol/L), give up to 250 mg/kg IM over 4 hours or 5 g (40 mEq) added to 1 liter of IV fluid infused over 3 hours. 1

Dosing Algorithm by Severity

Mild Hypomagnesemia (0.5-0.7 mmol/L or 1.2-1.7 mg/dL)

• First-line treatment: Administer 1 g magnesium sulfate (8.12 mEq) IM or IV every 6 hours for 4 doses (total 32.5 mEq per 24 hours). 1
• The IV injection rate should generally not exceed 150 mg/minute (1.5 mL of 10% concentration). 1
• Solutions for IV infusion must be diluted to 20% concentration or less prior to administration. 1

Severe Hypomagnesemia (<0.5 mmol/L or <1.2 mg/dL)

• For symptomatic or severe deficiency: Give up to 250 mg/kg (approximately 2 mEq/kg) IM within 4 hours if necessary. 1
• Alternative IV approach: Add 5 g magnesium sulfate (approximately 40 mEq) to 1 liter of 5% dextrose or 0.9% saline for slow IV infusion over 3 hours. 1
• For life-threatening arrhythmias or torsades de pointes: Administer 1-2 g IV bolus over 5 minutes, followed by continuous infusion if needed. 2, 3

Pediatric Dosing

• For hypomagnesemia/torsades with pulses: 25-50 mg/kg (maximum 2 g) IV/IO over 10-20 minutes. 2
• For pulseless torsades: 25-50 mg/kg (maximum 2 g) IV/IO given as bolus. 2
• Dilute to 20% concentration or less prior to IM injection in children. 1

Critical Safety Considerations

• Renal function is paramount: Establish adequate renal function before administering any magnesium supplementation, as exceeding renal excretory capacity can cause toxicity. 1, 4
• In severe renal insufficiency: Maximum dose is 20 g per 48 hours with frequent serum magnesium monitoring. 3, 1
• Monitor for toxicity: Watch for loss of patellar reflexes, respiratory depression, hypotension, and bradycardia during IV replacement. 3
• Have calcium chloride available to reverse magnesium toxicity if needed. 2

Administration Technique

• IV infusion: Dilute to 20% concentration or less; use 5% dextrose or 0.9% saline as diluent. 1
• IM injection: Deep IM injection of undiluted 50% solution is appropriate for adults; therapeutic levels achieved in 60 minutes. 1
• Do not mix magnesium sulfate with vasoactive amines or calcium in the same solution. 3
• Use central venous catheter when possible to avoid tissue injury from extravasation. 3

Special Clinical Scenarios

Cardiac Arrhythmias

• For torsades de pointes with prolonged QT: 1-2 g IV bolus over 5 minutes regardless of measured serum magnesium level. 5, 3
• For paroxysmal atrial tachycardia: 3-4 g (30-40 mL of 10% solution) IV over 30 seconds with extreme caution, only if simpler measures have failed. 1

Short Bowel Syndrome/High Output Stoma

• Initially use IV magnesium sulfate, then transition to oral magnesium oxide and/or 1-alpha cholecalciferol. 5
• Each liter of jejunostomy fluid contains approximately 100 mmol/L sodium; correct sodium and water depletion first to eliminate secondary hyperaldosteronism, which increases renal magnesium wasting. 2, 3

Pregnancy (Pre-eclampsia/Eclampsia)

• Total initial dose: 10-14 g magnesium sulfate. 1
• Give 4-5 g IV in 250 mL fluid, simultaneously with up to 10 g IM (5 g in each buttock). 1
• Subsequently, 4-5 g IM into alternate buttocks every 4 hours as needed, or 1-2 g/hour by continuous IV infusion. 1
• Critical warning: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities. 1

Common Pitfalls to Avoid

• Do not treat hypokalemia or hypocalcemia before correcting hypomagnesemia: Magnesium deficiency causes dysfunction of potassium transport systems and makes hypocalcemia/hypokalemia resistant to treatment. 3, 6
• Avoid rapid infusion: Can cause hypotension and bradycardia. 2
• Do not exceed 30-40 g total daily dose in most clinical situations. 1
• Parenteral magnesium should be reserved for symptomatic patients or those with severe deficiency (<1.2 mg/dL); asymptomatic mild cases can be treated orally. 4, 7