The oxytocin antagonist atosiban versus the β‐agonist terbutaline in the treatment of preterm labor

Objective. To compare the efficacy and safety of atosiban and terbutaline for the inhibition of preterm labor. Methods. Two hundred and forty‐nine women diagnosed with preterm labor at 23–33 weeks of gestation were enrolled of whom 245 women received treatment, 116 with atosiban and 129 with terbutaline. At randomization, women were stratified by gestational age (≤28 weeks and >28 weeks). Atosiban (iv bolus dose of 6.75 mg, then 300 μg/min for 3 h and 100 μg/min thereafter) and terbutaline (5–20 μg/min) were administered by iv infusion for 13–18 h. Re‐treatment with study drug or an alternative tocolytic agent was allowed. Tocolytic effectiveness was assessed in terms of the number of women undelivered after 48 hours and 7 days and efficacy and tolerability in terms of the number of women remaining undelivered and not requiring alternative tocolytic therapy after 48 hours and 7 days of starting therapy. Safety was assessed in terms of maternal side effects and neonatal morbidity. Results. Tocolytic effectiveness at 48 hours was 86.1% vs 85.3%; p =0.783, and after 7 days it was 76.5% vs 67.4%; p =0.067, in the atosiban and terbutaline groups, respectively. Tocolytic efficacy and tolerability after 48 hours was 72.2% vs 68.2%; p =0.51 and after 7 days was 55.6% vs 43.4%; p =0.08 in the atosiban and terbutaline groups, respectively. Overall, there were fewer clinically important adverse events with atosiban than with terbutaline. Conclusions. The efficacy of atosiban in the inhibition of preterm labor was shown to be comparable to terbutaline. Atosiban had a superior safety profile compared with terbutaline in terms of maternal and fetal adverse events, and comparable infant outcomes.