Nifedipine versus ritodrine for suppression of preterm labor. Comparison of their efficacy and secondary effects.

Objectives: To compare the efficacy of nifedipine and ritodrine in prolonging pregnancy beyond 48 h, 1 week and 36.0 weeks and to evaluate maternal side effects and adverse perinatal outcome.

Study Design: Non-blinded, randomized controlled trial. Eighty patients with singleton pregnancies admitted for preterm labor with intact membranes between 22 and 35 weeks of gestation were included in the study. Preterm labor was defined as the persistence of at least two symptomatic uterine contractions within a 10 min period during 60 min after admission and despite bed rest.

Results: Forty women received oral nifedipine and forty intravenous ritodrine. Two patients, one from each group, were excluded because of loss to follow-up after discharge. Therefore, 39 women in the nifedipine and the ritodrine groups, respectively, were evaluable for the final analysis. Baseline characteristics were comparable in both groups. The percentage of initial response, the speed of onset of action and the rate of successful treatment within 48 h were significantly better in the ritodrine group. However, prolongation of pregnancy beyond 7 days and 36 weeks of pregnancy was similar with a significantly lower rate of side effects in the nifedipine group.

Conclusions: In this small trial, ritodrine provided more effective tocolysis within the first 48 h than nifedipine at the doses used in this study, although with a significantly higher rate of side effects.