RESUMO
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 beta-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. 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. Nifedipine is recommended for aborting preterm contractions because it has fewer side-effects, superior efficacy and greater ease of administration than intravenous ritodrine