Pritchards regime
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Pritchard regime magnesium sulfate eclampsia protocol
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Pritchard's Regime (Magnesium Sulfate for Eclampsia)
Pritchard's regime is the classic intramuscular (IM) magnesium sulfate protocol for the prevention and treatment of eclamptic seizures in pre-eclampsia/eclampsia. It was developed by Dr. Jack A. Pritchard at Parkland Memorial Hospital, Dallas, and published in 1984 (Pritchard JA, Cunningham FG, Pritchard SA. Am J Obstet Gynecol 1984;148:951-963).
Indication
- Active eclampsia (seizures in the context of pre-eclampsia)
- Severe pre-eclampsia with imminent eclampsia (seizure prophylaxis)
Drug and Route
Magnesium sulfate (MgSO4) - given by a combination of IV and IM routes.
Dosing Schedule
Loading Dose (given simultaneously)
| Route | Dose | Detail |
|---|---|---|
| IV | 4 g | 20 mL of 20% solution over 3-5 minutes |
| IM (left buttock) | 5 g | 10 mL of 50% solution, undiluted |
| IM (right buttock) | 5 g | 10 mL of 50% solution, undiluted |
| Total loading | 14 g |
The simultaneous IV+IM loading gives a rapid therapeutic serum magnesium level.
Maintenance Dose
- 5 g IM (50% solution) in alternating buttocks every 4 hours
- Continue for 24 hours after delivery or 24 hours after the last seizure, whichever comes later
- Total dose over 24 hours of maintenance: ~30 g (plus 14 g loading = ~44 g total over 24 hours)
Monitoring During Therapy (MUST check before each maintenance dose)
| Parameter | Action |
|---|---|
| Patellar/knee reflex | Must be present - if absent, STOP MgSO4 |
| Respiratory rate | Must be ≥16/min - if reduced, STOP MgSO4 |
| Urine output | Must be ≥25 mL/hour (≥100 mL over 4 hours) |
| Serum Mg level (if available) | Therapeutic range: 4-8 mEq/L (4.8-9.6 mg/dL); loss of reflexes at ~10 mg/dL; respiratory arrest at ~12 mg/dL |
Antidote for Toxicity
Calcium gluconate 1 g IV (10 mL of 10% solution) given slowly over 5-10 minutes reverses hypermagnesemia. Keep it at the bedside.
Contraindications / Cautions
- Renal failure / severe oliguria (Mg is renally cleared - dose reduction required)
- Myasthenia gravis
- Respiratory depression
- Concurrent use of calcium channel blockers (potentiates effect)
- Cardiac conduction defects
Pritchard vs. Zuspan Regime (Comparison)
| Feature | Pritchard (IM) | Zuspan (IV) |
|---|---|---|
| Loading | 4 g IV + 10 g IM | 4-6 g IV only |
| Maintenance | 5 g IM every 4 h | 1-2 g/hour IV infusion |
| Total 24-hr dose | ~39 g | ~28-32 g |
| Setting | Resource-limited, no IV pump needed | Requires IV infusion pump |
| Administration | More painful at IM site | More controllable |
| Preferred in | LMICs, transfers, community | ICU/hospital with pumps |
Why IM in Pritchard?
The IM route is highly practical in low- and middle-income country settings where IV infusion pumps are unavailable. It can also be used as a loading-only dose (4 g IV + 10 g IM) for transfer of patients to higher facilities, then continued at the receiving center.
Key Points
- Pritchard's regime has a >95% seizure control rate in multiple trials
- It is the WHO-recommended regimen for resource-limited settings
- Oliguria is not a contraindication to administering the loading dose (only to maintenance)
- If seizures recur during therapy, an additional 2 g IV bolus can be given
- Delivery is the definitive treatment - MgSO4 controls seizures but does not treat the underlying cause
Sources: Rosen's Emergency Medicine (9780323757898); Creasy & Resnik's Maternal-Fetal Medicine (9780323828499); WHO/GH Supply Chain MgSO4 procurement guidance; Tygerberg Hospital MgSO4 Protocol
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