How should intravenous magnesium sulfate be diluted in normal saline (0.9% sodium chloride) for adult and pediatric patients, including recommended concentration, infusion rate, and monitoring?

Magnesium Sulfate Dilution in Normal Saline

Concentration and Dilution Requirements

For intravenous infusion, magnesium sulfate must be diluted to a concentration of 20% or less prior to administration. 1

• The most common diluents are 5% Dextrose Injection or 0.9% Sodium Chloride (normal saline). 1
• The undiluted 50% magnesium sulfate solution should never be given intravenously at full strength—it requires dilution for safe IV administration. 1

Standard Adult Dilution Protocols

For Severe Hypomagnesemia

• Add 5 g of magnesium sulfate (approximately 40 mEq) to 1 liter of normal saline for slow IV infusion over a 3-hour period. 1
• Alternatively, for rapid correction, up to 250 mg/kg (0.5 mL of 50% solution) may be given IM within 4 hours if necessary. 1

For Pre-eclampsia/Eclampsia

• Initial IV loading dose: Dilute 4-5 g of magnesium sulfate in 250 mL of normal saline and infuse over 15-30 minutes. 1
• Alternative rapid loading: Dilute the 50% solution to a 10% or 20% concentration; inject 40 mL of 10% solution (or 20 mL of 20% solution) IV over 3-4 minutes. 1
• Maintenance infusion: After loading, administer 1-2 g/hour by constant IV infusion. 1
• Target serum magnesium level of 6 mg/100 mL is optimal for seizure control. 1

For Cardiac Arrhythmias (Torsades de Pointes)

• Pediatric dose: 25-50 mg/kg IV over 10-20 minutes (faster in torsades de pointes), maximum dose 2 g. 2
• Adult dose: 2 g diluted in 50 mL of normal saline, infused at 50 mg/min, continued for 2 hours after arrhythmia resolution. 3

For Acute Severe Asthma

• Standard dose: 2 g magnesium sulfate diluted in 50 mL of 0.9% normal saline, infused over 15-20 minutes as adjunctive therapy. 4, 5
• Pediatric dose: 40 mg/kg (maximum 2 g) diluted in equivalent volume of normal saline, infused over 15-20 minutes. 5

For Renal Colic

• 15 mg/kg of magnesium sulfate 50% diluted in 100 mL normal saline, infused over 15 minutes. 6

Infusion Rate Guidelines

The rate of IV injection should generally not exceed 150 mg/minute (1.5 mL of a 10% concentration), except in severe eclampsia with seizures where faster administration may be necessary. 1

• For cardiac arrhythmias, a slower rate of 50 mg/min is recommended to minimize adverse effects. 3
• For emergency situations (torsades de pointes), faster infusion over 1-2 minutes is acceptable. 2
• For routine supplementation, infuse over 3 hours to prevent exceeding renal excretory capacity. 1

Pediatric-Specific Considerations

• IM administration in children: Dilute the 50% solution to 20% or less concentration before deep IM injection. 1
• TPN maintenance: Infants require 2-10 mEq (0.25-1.25 g) daily. 1
• For severe acute asthma in children, 40 mg/kg (maximum 2 g) shows significant improvement in peak expiratory flow rate and clinical asthma scores at 30 minutes compared to placebo. 5

Critical Monitoring Parameters

• Patellar reflex: Must remain present before each subsequent dose; absence indicates magnesium toxicity. 1
• Respiratory function: Ensure adequate respiratory rate (>12-16/min in adults) before continuing therapy. 1
• Serum magnesium levels: Target 6 mg/100 mL for seizure control; obtain frequent levels in renal insufficiency. 1
• Renal function: In severe renal insufficiency, maximum dosage is 20 g/48 hours with mandatory frequent serum monitoring. 1
• Urine output: Should maintain >30 mL/hour before continuing therapy. 1

Maximum Dosing Limits

• Total daily dose: Should not exceed 30-40 g in 24 hours. 1
• Pregnancy duration: Continuous maternal administration beyond 5-7 days can cause fetal abnormalities and must be avoided. 1
• Renal insufficiency: Maximum 20 g/48 hours. 1

Common Pitfalls to Avoid

• Never administer undiluted 50% solution intravenously—this causes severe tissue irritation and potential cardiac complications. 1
• Do not mix with phosphate-containing solutions in the same IV line, as precipitation may occur (though recent data suggests physical compatibility exists under specific conditions). 1, 7
• Avoid rapid infusion (>150 mg/min) except in life-threatening situations, as this causes flushing, hypotension, and cardiac depression. 1
• Do not continue beyond 5-7 days in pregnancy due to risk of fetal skeletal abnormalities. 1
• Check patellar reflexes before each dose—absent reflexes indicate impending respiratory depression. 1

Drug Incompatibilities

Magnesium sulfate may precipitate when mixed with solutions containing calcium, phosphates, or alkaline solutions; use separate IV lines when co-administering these agents. 1