Oral Nicardipine Versus Intravenous Ritodrine for the Treatment of Preterm Labor

Song, Tae Bok; Kim, Yoon Ha; Choi, Jin; Kang, Woo Dai; Oh, Yoon Sang; Kang, Myoung Seon; Cho, Moon Kyoung

Abstract

OBJECTIVE
This study was conducted to compare the efficacy and safety of oral nicardipine in acute therapy for preterm labor with those of parenteral ritodrine hydrochloride.
METHODS
Patients between 24 and 34 weeks' gestation with documented preterm labor were randomly assigned to receive oral nicardipine (n=31) or intravenous ritodrine (n=32) as initial tocolytic therapy. Patients in the nicardipine group received a 40-mg loading dose and then 20 mg every 2 hours as needed to stop contractions (total 80 mg). Patients in the ritodrine group received a 0.05 mg/min as initial dose. The dose was increased at 15-minute intervals until uterine contractions were inhibited or side effects became intolerable. The maximum recommended dose was 0.35 mg/min. Patients could be switched to another tocolytic regimen if they continued to have contractions after 6 hours of therapy. The main outcome variables examined were failure of tocolysis, time to uterine contractions equal or less than 5 times per hour, time to uterine quiescence, time gained in utero, and frequency of adverse medication effects.
RESULTS
There were no significant differences in maternal demographic characteristics between the groups. Successful tocolysis, defined as cessation of uterine contractons less than 6 hours from initial dose, was observed in 58.1% in the nicardipine group and 65.6% in the ritodrine group (P=.544). Among patients with successful tocolysis who responded with uterine quiescence within 6 hours, there was no significant difference in the time to uterine quiescence in the ritodrine group (P=.087). Time to uterine contractions equal or less than 5 times per hour from initial treatment showed no significant difference between the two groups with successful tocolysis (P=.097). The patients in the ritodrine hydrochloride group had more adverse side effects, mainly maternal tachycardia (P=.013) and nausea and/or vomiting (P=.006).
CONCLUSION
Oral nicardipine was effective, safe, and well-tolerated tocolytic agent. Patients who received ritodrine hydrochloride were more likely to have adverse medication effects.