Alternate Dosing Protocol for Magnesium Sulfate in Obese Women With Preeclampsia: A Randomized Controlled Trial.

OBJECTIVE

To evaluate whether obese women need greater doses of magnesium sulfate to obtain therapeutic serum concentrations for eclamptic seizure prevention.

METHODS

Women with preeclampsia and a body mass index (BMI) of 35 or higher were randomly allocated to either the Zuspan regimen of magnesium sulfate (4-g intravenous [IV] loading dose, then a 1-g/h infusion) or to alternate dosing (6-g IV loading dose, then a 2-g/h infusion). Women had serum magnesium concentrations obtained at baseline, as well as after administration of magnesium sulfate at 1 hour, 4 hours, and delivery. The primary outcome was the proportion of women who had subtherapeutic serum magnesium concentrations (less than 4.8 mg/dL) 4 hours after administration. A sample size of 18 women per group was planned to compare the proportion of women with subtherapeutic serum magnesium concentrations in each group.

RESULTS

From July 12, 2016, to March 14, 2019, 89 women with preeclampsia were screened and 37 were enrolled: 18 to the Zuspan regimen and 19 to the alternate regimen. A significantly greater proportion of women administered the Zuspan regimen had subtherapeutic serum magnesium concentrations at 4 hours (100% [95% CI 59-100] vs 63% [95% CI 41-81]; P=.01) compared with women administered the alternate higher dose regimen. At 4 hours, mean concentrations were significantly higher in the alternate regimen group (3.53 mg/dL±0.3 [Zuspan regimen] vs 4.41±0.5 [alternate regimen]; P<.01).

CONCLUSION

The alternate dosing regimen of a 6-g IV loading dose followed by a 2-g/h IV maintenance dose more reliably achieves therapeutic serum magnesium concentrations (as defined by a concentration of at least 4.8 mg/dL) in obese women with preeclampsia.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT02835339.