What is the recommended treatment for a patient with severe magnesium deficiency or at risk of life-threatening complications, including the dosage and administration of a magnesium flush?

Magnesium Flush for Severe Hypomagnesemia

Immediate Life-Threatening Presentations

For life-threatening complications including torsades de pointes, ventricular arrhythmias, seizures, or cardiac arrest, administer 1-2 g magnesium sulfate IV bolus over 5 minutes regardless of baseline magnesium level, followed by continuous infusion. 1, 2

Critical Indications for IV Magnesium "Flush"

• Cardiac emergencies: Torsades de pointes with prolonged QT interval requires 1-2 g magnesium sulfate IV bolus over 5 minutes, even if serum magnesium is normal 3, 1
• Severe symptomatic hypomagnesemia: Defined as <0.50 mmol/L (<1.2 mg/dL) with symptoms, requires 1-2 g IV bolus over 5-15 minutes followed by continuous infusion 1
• Cardiac arrest with known hyperkalemia: IV magnesium is recommended as part of standard ACLS care 3
• Neuromuscular crisis: Tetany, seizures, or altered consciousness require immediate hospitalization and IV magnesium 1, 4

Dosing Algorithm for Severe Deficiency

Initial Bolus Therapy

• Emergency bolus: 1-2 g (8-16 mEq) magnesium sulfate IV over 5 minutes for life-threatening presentations 1, 2
• Severe hypomagnesemia: Up to 250 mg/kg (approximately 2 mEq/kg) IM within 4 hours if necessary, or 5 g (40 mEq) added to 1 liter IV fluid for slow infusion over 3 hours 2
• Maximum infusion rate: Generally should not exceed 150 mg/minute (1.5 mL of 10% solution), except in severe eclampsia with seizures 2

Continuous Infusion Protocol

• Maintenance infusion: 2-4 mmol/hour (approximately 1-2 g/hour) to maintain plasma magnesium between 1.5-3 mmol/L 5
• Alternative regimen: 5 g (40 mEq) in 1 liter of D5W or normal saline infused over 3 hours 2
• Total daily dose: Should not exceed 30-40 g per 24 hours in patients with normal renal function 2

Critical Monitoring Requirements

Signs of Magnesium Toxicity

• Loss of patellar reflexes (first sign, occurs at 4-7 mEq/L) 1
• Respiratory depression (occurs at higher levels) 1
• Hypotension and bradycardia (can occur with rapid infusion) 1, 2
• Complete cardiovascular collapse at 6-10 mmol/L 1

Antidote Preparation

• Have calcium chloride 10% (5-10 mL) or calcium gluconate 10% (15-30 mL) immediately available to reverse magnesium toxicity if needed 1
• Administer calcium IV over 2-5 minutes if signs of toxicity develop 1

Renal Function Considerations

In severe renal insufficiency (GFR <30 mL/min), maximum dose is 20 grams per 48 hours with frequent serum magnesium monitoring. 1, 2

• Patients on dialysis require magnesium-enriched dialysis solutions to prevent ongoing losses 1
• Reduce doses and monitor closely in any degree of renal impairment 2

Essential Pre-Treatment Steps

Correct Volume Status First

• Address water and sodium depletion with IV saline before magnesium replacement to eliminate secondary hyperaldosteronism, which increases renal magnesium wasting 1, 4
• This is particularly critical in patients with high-output stomas, diarrhea, or gastrointestinal losses 1

Electrolyte Replacement Sequence

• Always replace magnesium BEFORE attempting to correct hypocalcemia or hypokalemia 1, 4
• Hypocalcemia and hypokalemia will be refractory to treatment until magnesium is normalized 1
• Calcium normalization typically occurs within 24-72 hours after magnesium repletion begins 1

Administration Precautions

Dilution Requirements

• Solutions for IV infusion must be diluted to 20% concentration or less prior to administration 2
• Common diluents are 5% dextrose or 0.9% sodium chloride 2
• Use central venous catheter when possible to avoid tissue injury from extravasation 1

Drug Incompatibilities

• Do not mix magnesium sulfate with calcium or vasoactive amines in the same solution 1
• Separate calcium and iron supplements from magnesium by at least 2 hours to avoid absorption interference 1

Special Clinical Scenarios

Pre-eclampsia/Eclampsia

• Total initial dose: 10-14 g magnesium sulfate 2
• IV component: 4-5 g in 250 mL fluid infused, or 4 g diluted to 10-20% given over 3-4 minutes 2
• IM component: Up to 10 g (5 g in each buttock) simultaneously 2
• Maintenance: 4-5 g IM into alternate buttocks every 4 hours, or 1-2 g/hour continuous IV infusion 2
• Target level: 6 mg/100 mL (approximately 2.5 mmol/L) for seizure control 2
• Critical warning: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities 2

Pediatric Dosing

• Severe hypomagnesemia with pulses: 25-50 mg/kg (maximum 2 g) IV/IO over 10-20 minutes 1
• Pulseless torsades: Same dose as bolus 1
• Dilute to 20% or less concentration for IM injection in children 2

Common Pitfalls to Avoid

• Do not delay ECG in patients with cardiac risk factors, QT-prolonging medications, heart failure, or digoxin therapy 1, 4
• Do not give bolus potassium for cardiac arrest suspected to be secondary to hypokalemia (Class III recommendation) 1
• Do not use oral magnesium alone in patients with short bowel syndrome or severe malabsorption—start with parenteral therapy 4
• Do not ignore concurrent electrolyte abnormalities—60-65% of critically ill patients have multiple electrolyte derangements 1, 6