Randomized comparison of intravenous nitroglycerin and magnesium sulfate for treatment of preterm labor

Objective: To compare the safety and efficacy of high-dose intravenous (IV) nitroglycerin with those of IV magnesium sulfate for acute tocolysis of pr eterm labor. Methods: Thirty-one women with preterm labor before 35 weeks' gestation wer e assigned randomly to IV magnesium sulfate or IV nitroglycerin for tocolys is. Preterm labor was defined as the occurrence of at least two contraction s in 10 minutes, with cervical change or ruptured membranes. Acute tocolysi s was defined as tocolysis for up to 48 hours. Magnesium sulfate was admini stered as a 4-g bolus, then at a rate of 2-4 g/h. Nitroglycerin was adminis tered as a 100-mu g bolus, then at a rate of 1 to 10-mu g/kg/min. The prima ry outcome measure was achievement of at least 12 hours of successful tocol ysis. Results: Thirty patients were available for analysis. There were no signifi cant differences in gestational age, cervical dilation, or incidence of rup tured membranes between groups at the initiation of tocolysis. Successful t ocolysis was achieved in six of 16 patients receiving nitroglycerin, compar ed with 11 of 14 receiving magnesium sulfate (37.5 Versus 78.6%, P = .033). Tocolytic failures (nitroglycerin versus magnesium sulfate) were due to pe rsistent contractions with cervical change or rupture of previously intact membranes (five of 16 versus two of 14), persistent hypotension (four of 16 versus none of 14, and other severe side effects tone of 16 versus one of 14). Maternal hemodynamic alterations were more pronounced in patients who received nitroglycerin, and 25% of patients assigned to nitroglycerin treat ment had hypotension requiring discontinuation of therapy. Conclusion: Tocolytic failures were more common with nitroglycerin than wit h magnesium sulfate. The hemodynamic alterations noted in patients receivin g nitroglycerin, including a 25% incidence of persistent hypotension, might limit the usefulness of IV nitroglycerin for the acute tocolysis of preter m labor. (C) 1999 by The American College of Obstetricians and Gynecologist s.