What is the recommended dosage and administration protocol for intravenous (IV) magnesium?

IV Magnesium Dosing and Administration

For most acute indications, administer 1-2 g IV magnesium sulfate over 15 minutes, with specific dosing protocols varying by clinical condition. 1, 2

Dosing by Clinical Indication

Torsades de Pointes / Polymorphic VT with QT Prolongation

• Administer 1-2 g IV over 15 minutes 1, 3
• This is first-line therapy regardless of serum magnesium level 3
• Have calcium chloride immediately available to reverse potential magnesium toxicity 1

Severe Preeclampsia / Eclampsia

• Loading dose: 4-6 g IV over 20-30 minutes 3, 2
• Maintenance: 1-2 g/hour continuous infusion 3, 2
• Alternative regimen: 4-5 g IV in 250 mL fluid infused simultaneously with 10 g IM (5 g in each buttock), then 4-5 g IM every 4 hours 2
• Continue for 24 hours postpartum as the standard recommendation 3
• Alternative approach: May discontinue after 8 g predelivery in select populations, though this requires consideration of local eclampsia incidence 3
• Research demonstrates 1 g/hour maintenance is as effective as 2 g/hour with fewer side effects 4
• Target therapeutic level: 1.8-3.0 mmol/L (approximately 4.3-7.2 mg/dL) 5

Severe Refractory Asthma

• Administer 2 g IV over 20 minutes 1, 3
• Must dilute to 20% or less concentration 2
• Evidence shows this reduces hospital admissions by approximately 7 per 100 patients treated 6
• Administer after oxygen, nebulized beta-agonists, and IV corticosteroids 6

Acute Hypomagnesemia

• Mild deficiency: 1 g (8.12 mEq) IM every 6 hours for 4 doses 2
• Severe deficiency: 5 g (40 mEq) in 1 liter fluid IV over 3 hours 2
• Alternative for severe cases: up to 250 mg/kg IM over 4 hours if necessary 2

Pediatric Dosing

• Hypomagnesemia/Torsades with pulses: 25-50 mg/kg (maximum 2 g) over 10-20 minutes 1
• Pulseless torsades: 25-50 mg/kg (maximum 2 g) by bolus 1
• Status asthmaticus: 25-50 mg/kg (maximum 2 g) over 15-30 minutes 1

Administration Rate and Safety

Maximum Infusion Rate

• Generally do not exceed 150 mg/minute (1.5 mL of 10% solution) 2
• Exception: severe eclampsia with active seizures may require faster administration 2
• Rapid infusion causes hypotension and bradycardia 1

Concentration Requirements

• Dilute to 20% or less concentration for IV infusion 2
• Common diluents: 5% dextrose or 0.9% sodium chloride 2
• For IM injection in children, dilute 50% solution to 20% or less 1

Maximum Daily Dosing

• Do not exceed 30-40 g total in 24 hours 2
• In severe renal insufficiency: maximum 20 g per 48 hours 2
• Do not continue beyond 5-7 days in pregnancy due to risk of fetal abnormalities 2

Monitoring Requirements

Clinical Monitoring

• Check deep tendon reflexes (patellar) before each dose 2, 5
• Loss of patellar reflex occurs at 3.5-5 mmol/L and signals impending toxicity 5
• Monitor respiratory rate continuously 2
• Respiratory paralysis occurs at 5-6.5 mmol/L 5
• Monitor urine output 2

Laboratory Monitoring

• Obtain serum magnesium levels with frequent or prolonged dosing 1
• Particularly critical in patients with impaired renal function 1
• Cardiac conduction alterations occur above 7.5 mmol/L 5
• Cardiac arrest expected when concentrations exceed 12.5 mmol/L 5

Critical Safety Considerations

Contraindications and Precautions

• Exercise extreme caution in renal insufficiency 2
• Monitor for common side effects: flushing, hypotension, bradycardia, CNS toxicity, respiratory depression 1, 6
• Have calcium chloride (20 mg/kg or 0.2 mL/kg of 10% solution) immediately available as antidote 1

Drug-Specific Warnings

• Do not mix with vasoactive amines or calcium 1
• Magnesium is a cofactor controlling sodium and potassium transport, affecting multiple cellular processes 1