Lifesavers · No. 25
Magnesium sulfate for eclampsia
Magnesium sulfate given to women with pre-eclampsia cut their risk of eclampsia by 58% in the largest trial ever conducted on the drug, and probably lowered the risk of maternal death as well.
Cases of eclampsia: 40 of 4,999 women given magnesium sulfate (0.8%) versus 96 of 4,993 given placebo (1.9%), 95% CI for the risk reduction 40 to 71. Maternal mortality was also lower with magnesium sulfate (relative risk 0.55, 95% CI 0.26 to 1.14), though that difference alone was not statistically significant on its own.
How it saves lives
Pre-eclampsia is a dangerous rise in blood pressure during pregnancy that can progress to eclampsia, in which the mother has seizures that endanger her and her baby. Magnesium sulfate is an old, cheap anticonvulsant that raises the seizure threshold and eases blood vessel spasm in the brain. Given by injection or infusion during labor or shortly after birth, it stops many of those seizures from ever happening.
The story
For most of the 20th century, doctors argued over which anticonvulsant, if any, actually prevented eclamptic seizures, with only small, inconclusive trials to point to. The Magpie Trial settled the question at a scale no one had managed before: 10,141 women with pre-eclampsia across 33 countries, randomly given magnesium sulfate or a placebo. Women who got the drug were 58% less likely to have an eclamptic seizure, and the trial's own investigators concluded it probably reduced the risk of the mother dying too. Magnesium sulfate is now on the World Health Organization's Model List of Essential Medicines for exactly this reason.
From the record
Women allocated magnesium sulphate had a 58% lower risk of eclampsia (95% CI 40-71) than those allocated placebo (40, 0.8%, vs 96, 1.9%; 11 fewer women with eclampsia per 1000 women).
Asked often
How much does magnesium sulfate reduce the risk of eclampsia?
The Magpie Trial, a randomized trial of 10,141 women with pre-eclampsia in 33 countries, found that magnesium sulfate cut the risk of eclampsia by 58% (95% CI 40 to 71) compared with placebo: 40 of 4,999 women given the drug had eclampsia versus 96 of 4,993 given placebo.
Who established that magnesium sulfate works for eclampsia?
No single inventor. Magnesium sulfate had been used for eclampsia since the early 1900s, but its benefit was only proven at scale by the Magpie Trial Collaborative Group, published in The Lancet in 2002.
The next one is being invented now.
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