A Comparison of Magnesium Sulfate and Nimodipine for the Prevention of Eclampsia

Abstract

Magnesium sulfate has been used for some time in the United States to prevent eclampsia. It dilates cerebral blood vessels and can reduce ischemia by preventing cerebral vasospasm. If eclampsia is in fact a result of cerebral ischemia, the calcium-channel blocker nimodipine, a specific cerebral vasodilator, would seem to be an ideal alternative treatment. Nimodipine can be given orally, has little toxicity, and lowers blood pressure. This unblinded trial randomized women with severe preeclampsia, for whom delivery had been decided on, to receive either 60 mg of nimodipine by mouth every 4 hours or a 6-g loading dose of magnesium sulfate followed by an infusion of 2 g per hour. An alternative was to administer 4 g at the outset to be followed by an infusion of 1 g per hour. Treatment continued for up to 24 hours antepartum. Participants were accessed from 14 centers in 8 countries. The 819 women randomized to receive nimodipine and the 831 given magnesium sulfate were comparable demographically and clinically, except for slightly higher baseline systolic blood pressure in the magnesium sulfate group. Mean arterial pressure fell by 8% on average within 1 hour of the start of treatment, and the reduction was maintained at 3 hours. Nimodipine-treated patients were significantly likelier to have a seizure than those given magnesium (2.6% vs. 0.8%). The crude relative risk of a seizure with nimodipine was 3.0. The majority of seizures in this group and all those in the magnesium sulfate group occurred in the antepartum period. The group difference in seizure risk was significant only in the postpartum period. Women given magnesium more often required hydralazine to control blood pressure and more frequently had postpartum bleeding. In addition, respiratory problems were more numerous in these patients. Rates of eclampsia were 1.4% in the nimodipine group and 0.5% in women given magnesium sulfate. This study shows that magnesium sulfate is a more effective means of preventing eclampsia in women with severe preeclampsia than is nimodipine. The findings suggest that eclampsia might be a result of cerebral overperfusion rather than decreased blood flow.