Magnesium sulfate.

Since the first American report on the use of magnesium sulfate tocolysis in 1977, its popularity as a tocolytic agent has increased progressively. Primarily because of its safety and familiarity, magnesium has become the primary tocolytic agent in the majority of U.S. centers. The exact mechanism of action is unknown, and long-term effects on neonates have not been studied. Although randomized studies show similar success compared to other tocolytic agents, no placebo-controlled study has shown neonatal improvement with magnesium sulfate tocolysis. This is similar to the studies of beta-sympathomimetic tocolytics and has led some authors (e.g., Higby) to suggest that safe dosages of magnesium sulfate are ineffective in preventing preterm birth and should not be used as a tocolytic agent. Although magnesium sulfate, like other tocolytics, has not fulfilled the initial promise of preventing preterm birth, it does appear if used correctly in a well identified population of patients to at least transiently inhibit preterm labor as well as other tocolytic agents with fewer side effects and fewer contraindications.