RESUMEN
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.