Magnesium sulfate has long been used to prevent seizures in women with eclampsia. It would be injected intrathecally (into the spinal cord), intravenously, and much later, intramuscularly.
Some health professionals recommend magnesium sulfate to prevent seizures in pregnant women with hypertension. Although the most widely prescribed antiepileptic drug is phenytoin, its use in obstetrics has been evaluated only in small doses, and its effectiveness in preventing eclampsia is not conclusive.
This randomized study was designed to compare intravenous and intramuscular magnesium sulfate with intravenous and oral phenytoin to prevent eclamptic convulsions in women with pregnancy-induced hypertension.
We randomly assigned women with hypertension who were admitted for delivery to receive either ten grams (g) of magnesium sulfate or phenytoin. Magnesium sulfate was administered intramuscularly (deep into the muscle) at the upper outer quadrant of each buttock. After which, a maintenance dose of five grams every four hours was given. An initial four-gram dose was given intravenously before the intramuscular doses for women with severe preeclampsia. Magnesium sulfate was continued for 24 hours after delivery.
The phenytoin regimen included a 1000-milligram (mg) loading dose infused for one hour, followed by a 500-mg oral dose ten hours later. Phenytoin was given only in the labor rooms because it needs special administration and monitoring. If it became necessary to transfer the patient to the delivery room before the phenytoin loading was completed, magnesium sulfate would be administered instead.
With either regimen, anticonvulsant therapy was continued for 24 hours postpartum.
Ten of 1089 women assigned to the phenytoin regimen had eclamptic convulsions. This result is significant compared with none of the 1049 placed in the magnesium sulfate group.
Magnesium sulfate is a better choice than phenytoin for preventing eclampsia in pregnant women with high blood pressure. These findings support the long-standing use of magnesium sulfate for preventing eclampsia.