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N Engl J Med. 1995 Jul 27;333(4):201-5.

A comparison of magnesium sulfate with phenytoin for the prevention of eclampsia.

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Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235-9032, USA.



Magnesium sulfate is used widely to prevent eclamptic seizures in pregnant women with hypertension, but few studies have compared the efficacy of magnesium sulfate with that of other drugs. Anticonvulsant prophylaxis with phenytoin for eclampsia has been recommended, but there are virtually no data to support its efficacy. Our objective was to compare magnesium sulfate with phenytoin in preventing seizures in hypertensive women during labor.


We randomly assigned women with hypertension who were admitted for delivery to receive either magnesium sulfate or phenytoin. The magnesium sulfate regimen consisted of a 10-g intramuscular loading dose followed by a maintenance dose of 5 g given intramuscularly every four hours. For women with severe preeclampsia, an additional 4-g loading dose was given intravenously. The phenytoin regimen included a 1000-mg loading dose infused over a period of 1 hour, followed by a 500-mg oral dose 10 hours later. With either regimen, anticonvulsant therapy was continued for 24 hours post partum.


Ten of 1089 women randomly assigned to the phenytoin regimen had eclamptic convulsions, as compared with none of 1049 women randomly assigned to magnesium sulfate (P = 0.004). There were no significant differences in any risk factors for eclampsia between the two study groups. Maternal and infant outcomes were also similar in the two study groups.


Magnesium sulfate is superior to phenytoin for the prevention of eclampsia in hypertensive pregnant women. These results validate the long-practiced use of magnesium sulfate in the prevention of eclampsia.

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