Magnesium Sulfate IV Infusion Dilution
Magnesium sulfate solutions for IV infusion must be diluted to a concentration of 20% or less prior to administration. 1
Standard Dilution Requirements
The FDA-approved labeling is explicit about concentration limits:
- All IV infusions require dilution to ≤20% concentration before administration 1
- The undiluted 50% solution is NOT appropriate for IV infusion and must be diluted 1
- Common diluents include 5% Dextrose Injection or 0.9% Sodium Chloride Injection 1
Clinical Application by Indication
Preeclampsia/Eclampsia
- Loading dose: 4-5g diluted in 250 mL of D5W or normal saline, infused IV 1
- Alternatively, dilute the 50% solution to 10% or 20% concentration (40 mL of 10% solution or 20 mL of 20% solution) and inject over 3-4 minutes 1
- Maintenance: 1-2g/hour by continuous IV infusion 2
Severe Asthma
Torsades de Pointes
- 1-2g IV over 15 minutes for polymorphic VT with QT prolongation 2
- First-line therapy regardless of baseline serum magnesium level 4, 3
Hypomagnesemia
- 5g (approximately 40 mEq) added to one liter of D5W or normal saline for slow IV infusion over 3 hours 1
- For acute severe cases: 1-2g IV over 15 minutes, followed by maintenance infusion of 1g/hour for 24 hours if needed 2
Critical Safety Parameters
Rate of Administration
- General maximum rate: 150 mg/minute (1.5 mL of 10% concentration or equivalent) 1
- Exception: severe eclampsia with active seizures may require faster administration 1
- Slower, cautious rates are essential to avoid hypermagnesemia 1
Maximum Dosing Limits
- Total daily dose should not exceed 30-40g in 24 hours 1
- In severe renal insufficiency: maximum 20g/48 hours with frequent serum level monitoring 1
- Continuous use in pregnancy beyond 5-7 days can cause fetal abnormalities 1
Monitoring Requirements
Clinical Monitoring
- Patellar reflex (knee jerk) must be present before each dose—absence indicates toxicity 1
- Respiratory rate ≥16 breaths/minute required before dosing 1
- Urine output ≥100 mL during 4 hours preceding each dose 1
Serum Magnesium Targets
- Therapeutic range for seizure control: 3-6 mg/100 mL (2.5-5 mEq/L) 1
- Deep tendon reflexes diminish when levels exceed 4 mEq/L 1
- Reflexes may be absent at 10 mEq/L, where respiratory paralysis becomes a hazard 1
Common Pitfalls to Avoid
- Never administer the 50% solution undiluted IV—this is only appropriate for IM injection in adults 1
- Have calcium immediately available to counteract magnesium toxicity 2, 1
- Exercise extreme caution in digitalized patients, as serious cardiac conduction changes and heart block may occur if calcium is needed to treat magnesium toxicity 1
- Reduce dosage in geriatric patients due to impaired renal function 1
- Common side effects include flushing, hypotension, and bradycardia with rapid administration 2, 4