In the Pritchard regimen for treating or preventing eclampsia in pregnant women, does the 24‑hour maintenance infusion of magnesium sulfate start from the loading dose or from the initiation of the maintenance infusion?

Timing of 24-Hour Magnesium Sulfate Maintenance in Pritchard Regimen

In the Pritchard regimen, the 24-hour maintenance period begins immediately after the loading dose is administered, not after the first maintenance dose. 1

Understanding the Pritchard Regimen Timeline

The Pritchard protocol consists of a combined loading dose followed by scheduled maintenance doses over 24 hours:

Loading Dose Components

• 4 grams intravenous magnesium sulfate is given first 1
• 10 grams intramuscular (5 grams in each buttock) is administered simultaneously 1, 2
• These together constitute a 14-gram loading dose 1, 2

Maintenance Dosing Schedule

• 5 grams intramuscular every 4 hours in alternating buttocks 1, 2
• This maintenance regimen continues for 24 hours total 1, 2
• The 24-hour clock starts from the time the loading dose is completed, not from when the first maintenance dose is given 1

Clinical Rationale for Timing

The maintenance infusion duration is calculated from the loading dose because therapeutic magnesium levels are established immediately after the loading dose is administered. 1 The loading dose rapidly achieves the target serum concentration, and the maintenance doses sustain that level throughout the 24-hour prophylactic period.

Postpartum Continuation

• Continue magnesium sulfate for at least 24 hours postpartum because eclamptic seizures may develop for the first time in the early postpartum period 3, 2
• The 24-hour postpartum duration is measured from delivery, representing an additional safety window beyond the antepartum/intrapartum treatment 3

Common Pitfall to Avoid

Do not restart the 24-hour clock with each maintenance dose. 1 If you were to count 24 hours from the first maintenance dose (given 4 hours after loading), you would inadvertently extend therapy to 28 hours total, which exceeds the evidence-based protocol and increases unnecessary magnesium exposure. The Pritchard regimen was validated in the MAGPIE trial with the 24-hour period beginning at the loading dose. 1, 2

Alternative IV Regimen for Comparison

When continuous intravenous infusion is available (preferred over Pritchard when IV access and pumps are readily available):

• Loading dose: 4–6 grams IV over 20–30 minutes 4, 3
• Maintenance: 1–2 grams per hour by continuous infusion for 24 hours 4, 3
• The 24-hour maintenance period similarly begins immediately after the loading dose is completed 4

Resource-Limited Settings Modification

In emergency situations where immediate transfer is needed:

• Give 10 grams IM total (5 grams in each buttock) as an emergency loading dose before transfer 1, 2
• This partial loading dose is better than no magnesium sulfate while arranging transport 1
• The receiving facility can then complete the full Pritchard protocol, counting the 24 hours from when the initial loading dose was given 1