What is the recommended MgSO4 (Magnesium Sulfate) regimen for managing preeclampsia?

Magnesium Sulfate Regimen for Preeclampsia

The recommended MgSO4 regimen for preeclampsia is a loading dose of 4-5g IV over 15-20 minutes, followed by a maintenance dose of 1-2g/hour by continuous IV infusion for 24 hours postpartum. 1, 2

Dosing Protocol

Loading Dose Options

• Standard IV Loading Dose: 4-5g IV in 250mL of 5% Dextrose or 0.9% Sodium Chloride over 15-20 minutes 1, 2
• Alternative Loading Dose (when IV not feasible): 4g IV followed by 5g IM in each buttock (total 14g loading) 1, 2

Maintenance Dose

• Standard Maintenance: 1-2g/hour by continuous IV infusion 1
• For Overweight Patients: Higher maintenance doses (2g/hour) for patients with BMI ≥25 kg/m² to achieve therapeutic levels 1, 3
• Duration: Continue for 24 hours postpartum to prevent eclampsia 1

Monitoring Requirements

Clinical Monitoring

• Deep tendon reflexes (first warning sign of toxicity is loss of patellar reflex)
• Respiratory rate (should be ≥12/min)
• Urine output (should be ≥30mL/hour)
• Level of consciousness
• Blood pressure every 4-6 hours 1

Laboratory Monitoring

• Serum magnesium levels (target: 4.8-8.4 mg/dL or >0.6 mmol/L) 1, 3
• Renal function (creatinine)
• Liver function tests
• Platelets and hemoglobin 1

Special Considerations

Indications for MgSO4 in Preeclampsia

MgSO4 should be given to women with:

• Preeclampsia with severe hypertension
• Preeclampsia with neurological signs/symptoms
• HELLP syndrome with co-existing severe hypertension
• As neuroprotection for preterm preeclampsia if delivery is required before 32 weeks' gestation 1

Fluid Management

• Restrict total fluid intake to 60-80 mL/hour during labor
• Aim for euvolemia by replacing insensible losses (30 mL/hour) plus urinary losses (0.5-1 mL/kg/hour)
• Avoid fluid overload which can lead to pulmonary edema in preeclamptic women 1

Safety Precautions

• Maximum daily dose should not exceed 30-40g in 24 hours 2
• In severe renal insufficiency, maximum dosage is 20g/48 hours with frequent serum magnesium monitoring 2
• Avoid continuous use beyond 5-7 days due to risk of fetal abnormalities 1, 2

Signs of Magnesium Toxicity

• Loss of patellar reflex: occurs at plasma concentrations between 3.5-5 mmol/L 4
• Respiratory depression: occurs at 5-6.5 mmol/L 4
• Cardiac conduction abnormalities: occur at >7.5 mmol/L 4
• Cardiac arrest: can occur when concentrations exceed 12.5 mmol/L 4

Route of Administration Considerations

The IV route is preferred when resources allow, as it results in:

• Fewer side effects
• Fewer injection site problems
• More consistent therapeutic levels 5

Common Pitfalls to Avoid

1. Inadequate Dosing in Overweight Patients: Standard 1g/hour maintenance may be insufficient in patients with BMI ≥25 kg/m² - consider 2g/hour 3
2. Premature Discontinuation: Stopping MgSO4 too early increases eclampsia risk, as seizures can still occur after delivery 1
3. Fluid Mismanagement: Both dehydration and fluid overload can be dangerous in preeclamptic patients 1
4. Insufficient Monitoring: Clinical monitoring of reflexes, respiration, and urine output is essential even if serum levels aren't measured 6
5. Prolonged Administration: Continuous use beyond 5-7 days can cause fetal abnormalities 1, 2

Recent evidence suggests that the Springfusor® pump for IV administration may be more acceptable to patients than the traditional IM regimen, with lower pain scores and fewer side effects 5, though this is not yet incorporated into guidelines.