A Prospective Randomized Study Comparing Nifedipine versus Ritodrine for the Suppression of Preterm Labour

Abstract

Nifedipine is a dihydropyridine and a calcium channel blocker during the second phase of the action potential of uterine smooth muscle cells, and ritodrine is a β-sympathomimetic. Objective of Study: To compare the efficacy and side-effects of oral nifedipine to ritodrine in the inhibition of preterm labour. Methodology: Sixty parturients admitted to the Maternity Hospital with preterm labour who fulfilled the inclusion criteria were randomized into two equal therapy groups: (a) oral nifedipine (n = 30) and (b) intravenous ritodrine (n = 30). During the period, the parturients were under continuous monitoring of fetal well-being, maternal uterine contractions, blood pressure, and pulse and respiratory rates. Both groups were given dexamethasone and followed up through delivery and the early neonatal period. Results: The incidence of preterm deliveries during the study period was 6.5%. Ritodrine had a quicker onset of inhibition of uterine contractions, especially between 20 and 40 min after initiation of tocolytic therapy (p < 0.04). Labour was delayed on the average for 40 h in the nifedipine group compared to 24 h in the ritodrine group (p < 0.05). Eighteen patients (60%) in the nifedipine group had cessation for more than 48 h compared to 7 (30.4%) in the ritodrine group (p < 0.05). Nifedipine inhibited uterine contractions for more than 7 days in more patients than ritodrine (13 versus 5, p < 0.05). Ten patients in the nifedipine group went beyond 36 weeks of gestation compared to 4 in the ritodrine group (p < 0.03). In 5 (17.9%) of the ritodrine group compared to none in the nifedipine group, treatment was abandoned because of severe side-effects of nausea (11 versus 2, p < 0.01) and palpitations (16 versus 3, p < 0.004). There were no significant differences in the Apgar scores and neonatal morbidity. More infants in the ritodrine group (17, 73.9%) than in the nifedipine group (14, 46.1%, p < 0.05) were admitted to the neonatal unit. Conclusion: Nifedipine is recommended for aborting preterm contractions because it has fewer side-effects, superior efficacy and greater ease of administration than intravenous ritodrine.