Administration of 1 gram Magnesium Sulfate
For a 1 gram dose of magnesium sulfate, administer intravenously over 15 minutes for acute hypomagnesemia or as part of a maintenance infusion at 1 gram/hour for conditions like preeclampsia, or give intramuscularly every 6 hours for mild magnesium deficiency. 1, 2
Route and Frequency by Clinical Indication
Torsades de Pointes (Polymorphic VT with QT Prolongation)
- Administer 1-2 grams IV over 15 minutes as first-line therapy, diluted in 10 mL D5W 1, 3, 4
- This is effective regardless of baseline serum magnesium levels 4
- Do NOT use magnesium sulfate for any other cardiac arrest rhythm (VF, pVT, asystole, PEA) as it provides no benefit 3
Acute Hypomagnesemia
- For mild deficiency: 1 gram IM every 6 hours for four doses (total 4 grams over 24 hours) 2
- For acute IV replacement: 1-2 grams IV over 15 minutes, followed by maintenance infusion of 1 gram/hour for 24 hours if needed 1
- For severe hypomagnesemia: up to 5 grams can be added to 1 liter of D5W or normal saline for slow IV infusion over 3 hours 2
Preeclampsia/Eclampsia Maintenance
- After a loading dose of 4-6 grams IV, continue maintenance infusion at 1-2 grams/hour 1
- The 1 gram/hour maintenance dose is as effective as 2 grams/hour with fewer side effects in standard-weight patients 5
- For overweight patients (BMI ≥25 kg/m²), use 2 grams/hour maintenance as 1 gram/hour frequently results in subtherapeutic levels 6, 7
- Continue for 24 hours postpartum as the standard recommendation 1
Other Seizure Disorders
- For seizures associated with epilepsy, glomerulonephritis, or hypothyroidism: 1 gram administered IM or IV 2
Critical Administration Guidelines
IV Administration Safety
- Never exceed 150 mg/minute (1.5 mL of 10% solution) for IV push, except in severe eclampsia with active seizures 2
- Dilute to 20% concentration or less before IV infusion 8, 2
- Common side effects include flushing, hypotension, and bradycardia 1
IM Administration
- The undiluted 50% solution is appropriate for adults IM 2
- Dilute to 20% or less concentration for children 2
- IM administration achieves therapeutic plasma levels in 60 minutes, whereas IV provides immediate levels 2
Monitoring Requirements
Toxicity Prevention
- Loss of patellar reflex occurs at 3.5-5 mmol/L (first warning sign) 9
- Respiratory paralysis occurs at 5-6.5 mmol/L 9
- Cardiac arrest risk when concentrations exceed 12.5 mmol/L 9
- Monitor deep tendon reflexes, respiratory rate (must be >12/min), and urine output (must be >25-30 mL/hour) 9
Therapeutic Levels
- Target serum magnesium: 1.8-3.0 mmol/L (4.8-8.4 mg/dL) for seizure prophylaxis 9, 6
- For preeclampsia, 6 mg/100 mL is considered optimal for seizure control 2
Important Caveats
- Have calcium gluconate immediately available to counteract magnesium toxicity 1
- Do not exceed 30-40 grams total daily dose 2
- In severe renal insufficiency, maximum dose is 20 grams/48 hours with frequent serum level monitoring 2
- Do not continue magnesium sulfate in pregnancy beyond 5-7 days as it can cause fetal abnormalities 2
- Body mass index significantly affects serum magnesium levels—higher BMI correlates with lower levels at standard dosing 6, 10