73: A randomized double-blinded placebo-controlled trial of nifedipine for acute tocolysis of preterm labor

Abstract

Nifedipine is frequently used for acute tocolysis of preterm labor, despite there being no reports of its effectiveness compared to placebo. We sought to compare the effectiveness of nifedipine to placebo. We conducted a randomized, double-blind, placebo-controlled trial of nifedipine. Women ages 16-44 who had documented uterine activity and who were at risk of preterm birth were included if they had a singleton pregnancy with intact membranes between 28-0/7 and 33-6/7 weeks’ gestation and cervical dilatation between 2 and 4 cm. Women who consented to participate were randomized and received nifedipine 20 mg or placebo orally, then nifedipine 20 mg or placebo orally after 90 minutes if still contracting. Nifedipine 20 mg or placebo was continued orally every 4 hours after the first dose, for 48 hours. The protocol specified that a total of 150 patients be included, but after a pre-planned interim analysis, the Data Safety Monitoring Committee recommended discontinuation of the trial due to futility. The study was terminated after randomization of a total of 88 subjects with data available for analysis: 46 for nifedipine and 42 for placebo. Nifedipine did not affect blood pressure in normotensive women, but heart rates were significantly increased after the first 4 hours and at the end of the 48-hour window. Despite this physiologic effect, there were no statistically significant differences in the primary or prespecified secondary outcomes (Table). The rate of discontinuation for side effects did not differ. There were no stillbirths and no significant differences in neonatal outcomes. Acute tocolysis of preterm labor with nifedipine did not affect preterm birth rates, with the interim analysis demonstrating futility for study continuation.