OBJECTIVE: To compare oral rofecoxib with intravenous magnesium sulfate as a tocolytic. METHODS: This was a randomized study of patients who were between 22 and 34 weeks of gestation with preterm labor. Patients were randomly assigned to receive either daily oral rofecoxib (50 mg) or intravenous magnesium sulfate for a maximum of 48 hours. Outcome variables included delay of delivery for 48 hours and the incidence of side effects. Data were analyzed by using the Student t test, Mann-Whitney U test, X2 test, and repeated-measures analysis of variance. Sample size calculations were based on previous studies of tocolytic efficacy. RESULTS: Two hundred fourteen patients were randomly assigned (105 received rofecoxib and 109 received magnesium sulfate). Delivery was delayed for 48 hours in 95 (90.4%) and 96 (88%) of the patients in the rofecoxib and magnesium sulfate groups, respectively (relative risk 0.97; 95%confidence interval 0.89, 1.06). To show a statistically significant benefit in delay of delivery past 48 hours, a total of 2,686 patients would be required in each group. There was no difference between the groups over the course of the study in cervical dilatation, amniotic fluid index, or cervical length by vaginal ultrasonography. The median hospital days on the original admission were also similar at 2 for both groups (P = .10). There was a higher reported incidence of maternal side effects in the magnesium sulfate group (relative risk 1.81; 95%confidence interval 1.07, 3.06). There was no difference in the incidence of neonatal side effects. CON CLUSION: There was no difference between oral rofecoxib and intravenous magnesium sulfate in arresting preterm labor. OBJECTIVE: To compare oral rofecoxib with intravenous magnesium sulfate as a tocolytic. METHODS: This was a randomized study of patients who were between 22 and 34 weeks of gestation with preterm labor. Patients were randomly assigned to receive either daily oral rofecoxib (50 mg) or intravenous magnesium sulfate for a maximum of 48 hours. Outcome variables included delay of delivery for 48 hours and the incidence of side effects. Data were analyzed by using the Student t test, Mann-Whitney U test, X2 test, and repeated-measures analysis of variance. Sample size calculations were based on previous studies of tocolytic efficacy. RESULTS: Two hundred fourteen patients were randomly assigned (105 received rofecoxib and 109 received magnesium sulfate). Delivery was delayed for 48 hours in 95 (90.4%) and 96 (88%) of the patients in the rofecoxib and magnesium sulfate groups, respectively (relative risk 0.97; 95% confidence interval 0.89, 1.06). To show a statistically significant benefit in there was no difference between the groups over the course of the study in cervical dilatation, amniotic fluid index, or cervical length by vaginal ultrasonography. The median hospital days on the original admission were also similar at 2 for both groups (P = .10). There was a higher reported incidence of maternal side effects in the magnesium sulfate group (relative risk 1.81; 95% confidence interval 1.07, 3.06). There was no difference in the incidence of neonatal side effects. CON CLUSION: There was no difference between oral rofecoxib and intravenous magnesium sulfate in arresting preterm labor.