What is the recommended treatment regimen for a pregnant woman with severe preeclampsia, specifically the Sibai regimen?

Sibai Regimen for Severe Preeclampsia

The Sibai regimen consists of magnesium sulfate administered as a 4-5g IV loading dose over 5 minutes, followed by a 1-2g/hour continuous IV infusion, combined with simultaneous IM injections of 5g (10 mL of 50% solution) into each buttock, with subsequent 4-5g IM doses every 4 hours as needed based on patellar reflexes and respiratory function. 1, 2

Loading Dose Protocol

The initial approach involves dual-route administration:

• IV component: 4-5g magnesium sulfate diluted in 250 mL of 5% dextrose or 0.9% sodium chloride, infused over 3-4 minutes 1
• IM component: Simultaneously administer 5g (10 mL of undiluted 50% solution) deep IM into each buttock for a total of 10g 1
• Total initial dose: 14-15g magnesium sulfate 1

Maintenance Dosing Options

After the loading dose, two maintenance approaches are acceptable:

Option 1: Intermittent IM Dosing (Traditional Sibai)

• Administer 4-5g (8-10 mL of 50% solution) IM into alternate buttocks every 4 hours 1
• Continue until paroxysms cease 1
• This approach requires checking patellar reflexes before each dose 1

Option 2: Continuous IV Infusion (Modern Alternative)

• Maintain 1-2g/hour continuous IV infusion 3, 1
• This method allows for easier titration and monitoring 3

Critical Safety Monitoring

Before administering each dose, verify three essential parameters:

• Patellar reflexes present: Absence indicates magnesium levels >10 mEq/L with risk of respiratory paralysis 1
• Respiratory rate ≥12-16 breaths/minute: Respiratory depression occurs at toxic levels 3, 1
• Urine output ≥100 mL/4 hours (or ≥30 mL/hour): Oliguria increases toxicity risk as magnesium is renally excreted 3, 1

Therapeutic Target and Duration

• Target serum magnesium level: 3-6 mg/100 mL (2.5-5 mEq/L) for seizure control 1
• Duration: Continue for 24 hours postpartum in most cases 3
• Maximum total daily dose: 30-40g in 24 hours 1
• Never exceed 5-7 days: Continuous administration beyond this causes fetal skeletal abnormalities 1

Concurrent Blood Pressure Management

Magnesium sulfate does NOT control blood pressure—it only prevents seizures 3. For severe hypertension (≥160/110 mmHg):

• First-line agent: IV labetalol 20mg bolus, then 40mg after 10 minutes, then 80mg every 10 minutes to maximum 220mg 4
• Alternative: Oral nifedipine (immediate-release) 5
• Target BP: Systolic 110-140 mmHg and diastolic 85 mmHg 6, 4

Critical Contraindications and Warnings

Never combine magnesium sulfate with calcium channel blockers (especially IV or sublingual nifedipine)—this causes severe myocardial depression and precipitous hypotension. 3, 4 If nifedipine is needed for blood pressure control, use oral immediate-release formulation with extreme caution and close monitoring 6.

Antidote for Toxicity

Keep 10 mL of 10% calcium gluconate (1g) IV immediately available at bedside 3. Administer over 3 minutes if signs of magnesium toxicity develop (absent reflexes, respiratory rate <12, respiratory depression) 3.

Special Circumstances

Renal Impairment

• Maximum dose: 20g/48 hours 1
• Obtain frequent serum magnesium levels 1
• Reduce maintenance dose or extend dosing intervals 1

Postpartum Administration

• Continue for minimum 24 hours postpartum as eclamptic seizures may develop for the first time in early postpartum period 5
• Monitor BP and clinical condition at least every 4 hours while awake for at least 3 days postpartum 5

Common Pitfalls to Avoid

• Do not rely on serum magnesium levels for routine monitoring—clinical assessment (reflexes, respiratory rate, urine output) is sufficient and more practical 3
• Do not use diuretics—they further reduce plasma volume which is already contracted in preeclampsia 6
• Do not delay treatment waiting for laboratory confirmation—initiate magnesium sulfate immediately for severe preeclampsia with neurological symptoms 6
• Do not use plasma volume expansion routinely—this increases pulmonary edema risk 6

Evidence Base

The Sibai regimen is supported by multiple randomized controlled trials involving over 4,000 women demonstrating magnesium sulfate reduces eclampsia risk by 61% (relative risk 0.39,95% CI 0.28-0.55) with a number needed to treat of 71-100 3, 7, 8. This protocol has been uniformly recommended by ISSHP (2018), European Society of Cardiology, and ACOG as first-line therapy for severe preeclampsia and eclampsia 3, 2, 9.