What are the clinical uses and dosing guidelines for Magnesium Sulfate (MgSO4)?

Clinical Uses and Dosing Guidelines for Magnesium Sulfate (MgSO4)

Magnesium sulfate is primarily indicated for the prevention and treatment of seizures in severe preeclampsia and eclampsia, with specific dosing regimens established for these conditions, as well as for treatment of hypomagnesemia and other select clinical scenarios. 1

Primary Clinical Indications

1. Preeclampsia and Eclampsia

• Severe preeclampsia: For seizure prophylaxis during labor and for 24 hours postpartum 1
• Eclampsia: For treatment of seizures and prevention of recurrent seizures 1, 2

2. Magnesium Deficiency

• Mild to severe hypomagnesemia 3
• Refractory hypokalemia 1

3. Other Uses

• Fetal neuroprotection in preterm birth 4
• Counteracting barium poisoning 3
• Management of seizures associated with epilepsy, glomerulonephritis, or hypothyroidism 3
• Paroxysmal atrial tachycardia (when simpler measures have failed) 3
• Reduction of cerebral edema 3

Dosing Guidelines

For Severe Preeclampsia/Eclampsia:

Loading Dose:

• 4-5 g IV in 250 mL of 5% Dextrose or 0.9% Sodium Chloride over 15-20 minutes 1, 3

Maintenance Dose Options:

1. IV Regimen: 1-2 g/hour by constant IV infusion for 24 hours postpartum 1, 3

   • Higher maintenance doses (2 g/hour) for overweight patients (BMI ≥25 kg/m²) 1
   • Reduced dose (0.5-0.75 g/hour) for patients with impaired renal function 1

2. IM Regimen: 5 g IM every 4 hours in alternating buttocks 1, 3

   • After initial IV loading dose of 4-5 g, 10 g IM (5 g in each buttock) followed by 5 g IM every 4 hours 3

For Magnesium Deficiency:

Mild Deficiency:

• 1 g (8.12 mEq) IM every 6 hours for 4 doses 3

Severe Hypomagnesemia:

• Up to 250 mg/kg IM within a 4-hour period, or
• 5 g (40 mEq) added to 1 L of IV fluid for slow infusion over 3 hours 1, 3

Therapeutic Levels and Monitoring

Target Serum Levels:

• 1.8-3.0 mmol/L for eclampsia treatment 1, 2
• Minimum 0.6 mmol/L (1.5 mg/dL) to prevent hypomagnesemia 1

Clinical Monitoring:

• Deep tendon reflexes: Loss occurs at 3.5-5 mmol/L 1, 2
• Respiratory rate: Respiratory depression at 5-6.5 mmol/L 2
• Urine output: Should be at least 30 mL/hour 1, 2
• Level of consciousness 1

Signs of Toxicity:

• ECG changes (prolonged PR, QRS, QT) at 2.5-5 mmol/L 1
• Loss of tendon reflexes, sedation, muscle weakness at 4-5 mmol/L 1
• Respiratory depression at 5-6.5 mmol/L 2
• Cardiac conduction abnormalities at >7.5 mmol/L 2
• Cardiac arrest at >12.5 mmol/L 2

Important Considerations and Precautions

Duration of Treatment:

• Should not normally exceed 24 hours 5
• Continuous use in pregnancy beyond 5-7 days can cause fetal abnormalities 3

Fluid Management:

• Total fluid intake should be restricted to 60-80 mL/hour during labor 1
• Aim for euvolemia by replacing insensible losses (30 mL/hour) plus anticipated urinary losses (0.5-1 mL/kg/hour) 1

Antidote for Toxicity:

• Calcium chloride (10%) 5-10 mL or calcium gluconate (10%) 15-30 mL should be immediately available 1

Drug Interactions:

• Avoid concomitant use with calcium channel blockers due to risk of severe hypotension 1
• May reduce antibiotic activity of streptomycin, tetracycline, and tobramycin 3
• Drugs that may exacerbate hypomagnesemia: proton-pump inhibitors, macrolides, fluoroquinolones, gentamicin, and antiviral drugs 1

Special Populations:

• Maximum dosage in severe renal insufficiency: 20 g/48 hours with frequent serum magnesium monitoring 3
• Lower maintenance dose (1 g/hour) may be as effective as higher dose (2 g/hour) with fewer side effects 6

Clinical Pearls

• Serum monitoring is not always necessary if clinical monitoring (respiration, reflexes, urine output) is adequate 5
• IM administration is suitable in low-resource settings but may cause more injection site problems 5
• The low-dose IM regimen (Dhaka regimen) has been shown to be equally efficacious with fewer side effects compared to IV regimens 7
• Administration can be done by properly trained medical, midwife, or nursing staff 5