Nifedipine compared with atosiban for treating preterm labor: a randomized controlled trial.

To compare the tocolytic efficacy and tolerability of nifedipine with that of atosiban among pregnant women with preterm labor. Pregnant women admitted with preterm labor and intact membranes between 24 and 33 weeks 6 days of gestation, between January 2008 and December 2011, were randomly assigned to either atosiban or nifedipine treatment. Assigned treatment was planned for up to 48 hours. If progress was determined after 1 hour or more, a crossover of the study drugs was performed. The primary outcome was to estimate the tocolytic efficacy and tolerability profile that was assessed in terms of the proportion of women who were not delivered and did not require an alternate tocolytic agent within 48 hours. Secondary outcomes were gestational age at delivery and neonatal morbidity. Seventy-five women in the nifedipine group and 70 in the atosiban group were included and analyzed. Baseline demographic and obstetric characteristics were comparable. Forty-eight (68.6%) women allocated to atosiban and 39 (52%) to nifedipine did not deliver and did not require an alternate agent at 48 hours respectively (P=.03). At 7 days from enrollment, 55 (78.6%) women allocated to atosiban and 67 (89.3%) to nifedipine remained undelivered with or without a rescue agent (P=.02). Mean gestational age at delivery was 35.2 (±3.0) and 36.4 (±2.8) weeks among the atosiban and nifedipine groups, respectively (P=.01). Mean birth weight and neonatal morbidity were comparable. Atosiban has fewer failures within 48 hours. Nifedipine may be associated with a longer postponement of delivery. ClinicalTrials.gov, www.clinicaltrials.gov, NCT00599898.