Double-blind, randomized, controlled trial of atosiban and ritodrine in the treatment of preterm labor: A multicenter effectiveness and safety study

OBJECTIVE: This study was undertaken to compare the efficacy and safety of intravenous administration of atosiban versus ritodrine for the treatment o f preterm labor. STUDY DESIGN: Women with preterm labor and intact membranes diagnosed at 23 to 33 gestational weeks (n = 247) were randomly assigned to treatment arms and received atosiban (6.75 mg intravenous bolus, 300 mu g/min for 3 hours , then 100 mu g/min intravenously) or ritodrine (0.10-0.35 mg/min intraveno usly) for as long as 18 hours. Tocolytic effectiveness was assessed in term s of the numbers of women who had not been delivered after 48 hours and aft er 7 days. Safety was assessed in terms of maternal side effects and neonat al morbidity. Secondary outcomes included mean gestational age at delivery and mean birth weight. An intent-to-treat analysis was performed with the C ochran-Mantel-Haenszel test. RESULTS: The proportion of women who had not been delivered at 48 hours was 84.9% (n = 107) in the atosiban group and 86.8% (n = 105) in the ritodrine group. At 7 days 92 women had still not been delivered in both the atosiba n (73.0%) and ritodrine (76.0%) groups. Neither of these differences was st atistically significant. The incidence of maternal cardiovascular side effe cts was substantially lower in the atosiban group (4.0% vs 84.3%, P<.001). In addition, intravenous therapy was terminated more frequently as a result of maternal adverse events in the ritodrine group (29.8%) than in the atos iban group (0.8%). The overall occurrences of fetal adverse events in the t wo treatment groups were comparable. Neonatal morbidity was similar between the treatment groups after adjustment for unbalanced enrollment of women w ith multiple pregnancies and for gestational ages within treatment groups. CONCLUSION: Atosiban was comparable in clinical effectiveness to convention al ritodrine therapy but was better tolerated than ritodrine, with no evide nce of significant maternal or fetal adverse events. Neonatal morbidity, wh ich was similar between the two treatment arms, was apparently related to t he gestational age of the infant rather than to the exposure to either toco lytic agent.