A prospective, randomized, controlled trial of high and low maintenance doses of magnesium sulfate for acute tocolysis

Objective: This study was undertaken to compare a high-dose protocol for magnesium sulfate tocolytic therapy with a low-dose regimen with respect to time needed to achieve tocolysis. Study Design: Patients between 24 and 34 weeks’ gestation with preterm labor were included. Patients with ruptured membranes or nonreassuring fetal assessments were excluded. Gravid women received a 4-g loading dose of magnesium sulfate and were prospectively randomly assigned to receive a maintenance dose of 2 or 5 g/h. Results: The median times to tocolysis were 120 minutes (semi-interquartile range, 30 minutes) in the low-dose group and 90 minutes (semi-interquartile range, 28 minutes) in the high-dose group (P< .001). Conclusion: Patients treated with a higher maintenance dose of magnesium sulfate had a higher frequency of side effects; however, tocolysis was achieved more rapidly and they required shorter admissions to the labor and delivery unit without increased maternal or neonatal morbidity. (Am J Obstet Gynecol 2000;182:1477-82.)