What is the recommended treatment regimen for pregnant women at risk of pre-eclampsia or eclampsia using Magnesium Sulfate (MgSO4)?

Pritchard Regimen for Magnesium Sulfate in Pre-eclampsia/Eclampsia

The Pritchard regimen consists of a combined loading dose of 4 grams IV over 20-30 minutes plus 10 grams IM (5 grams in each buttock), followed by maintenance doses of 5 grams IM every 4 hours in alternate buttocks for 24 hours postpartum. 1, 2

Loading Dose Protocol

The Pritchard protocol is specifically designed for settings with limited IV access or as an alternative to continuous IV infusion 1:

• Initial loading: 4 grams IV (as 20% solution) over 10-15 minutes PLUS simultaneously 10 grams IM (5 grams deep IM in each buttock using undiluted 50% solution) 2, 3
• This combined approach provides immediate therapeutic levels from the IV component while the IM doses create a depot effect 4

Maintenance Dosing

After the loading dose 1, 2:

• 5 grams IM every 4 hours in alternate buttocks
• Continue for 24 hours postpartum in most cases 1, 5
• The IM route achieves therapeutic plasma levels within 60 minutes, whereas IV provides almost immediate levels 2

When to Use Pritchard vs. Standard IV Regimen

Pritchard regimen advantages:

• Resource-limited settings where continuous IV infusion pumps are unavailable 1
• Can be administered by trained midwives or nursing staff without requiring continuous IV monitoring 6
• Particularly suitable for low and middle-income countries 5

Standard IV regimen (alternative):

• 4-6 grams IV loading over 20-30 minutes, then 1-2 grams/hour continuous infusion 1
• Preferred when IV access and infusion pumps are readily available 1
• 2 grams/hour maintenance is more effective than 1 gram/hour, especially in patients with BMI ≥25 kg/m² 1

Critical Safety Monitoring

Before each IM dose, verify all three criteria 2:

• Patellar reflex present (knee jerk) - reflexes disappear at 10 mEq/L, indicating impending toxicity 2
• Respiratory rate ≥12-16 breaths/minute - respiratory paralysis occurs at 5-6.5 mmol/L 2, 4
• Urine output ≥30 mL/hour - magnesium is renally excreted and oliguria increases toxicity risk 6

If any of these are absent, hold the dose and do not give additional magnesium until they return 2

Therapeutic and Toxic Levels

Target therapeutic range 4:

• 1.8-3.0 mmol/L (or 3-6 mg/100 mL) for seizure control 2, 4
• Patellar reflexes diminish at 3.5-5 mmol/L 4
• Respiratory paralysis at 5-6.5 mmol/L 4
• Cardiac arrest risk >12.5 mmol/L 4

Serum magnesium monitoring is NOT routinely needed - clinical monitoring (reflexes, respiratory rate, urine output) is sufficient 6. Only check levels in renal impairment or suspected toxicity 6.

Duration of Therapy

• Standard duration: 24 hours postpartum 1, 5
• Some evidence suggests women who received ≥8 grams before delivery may not benefit from continuing the full 24 hours, but the 24-hour protocol remains the safer standard 1, 5
• Never exceed 5-7 days of continuous administration as this causes fetal abnormalities 5, 2
• Maximum total dose: 30-40 grams per 24 hours 2
• In severe renal insufficiency: maximum 20 grams per 48 hours 2

Critical Drug Interactions and Contraindications

Absolute contraindications to combining medications 6, 1:

• Never combine with calcium channel blockers (especially IV or sublingual nifedipine) - causes severe myocardial depression and precipitous hypotension 6, 1, 5
• Reduce doses of CNS depressants (barbiturates, narcotics, anesthetics) due to additive effects 2
• Use extreme caution with cardiac glycosides (digoxin) - can cause heart block 2

Fluid Management

Limit total fluid intake to 60-80 mL/hour to prevent pulmonary edema in preeclamptic patients with capillary leak 1, 5. Avoid both fluid overload and "running dry" as these patients are at risk for acute kidney injury 5.

Common Pitfalls

• Avoid NSAIDs for postpartum pain in preeclamptic patients - worsens hypertension and increases acute kidney injury risk 1
• Have calcium gluconate immediately available as antidote for magnesium toxicity 4
• Remember preeclampsia may worsen or appear de novo postpartum, particularly days 3-6 5
• The undiluted 50% solution can be used for IM injection in adults but must be diluted to ≤20% for IV use or IM use in children 2