Objective: This study was conducted to compare the safety and efficacy of transdermal glyceryl trinitrate (GTN) in initial therapy for preterm labor with those of intravenous ritodrine hydrochloride and the effects of tocolytics in uteroplacental circulation, as assessed by uterine artery doppler velocimetry.
Methods: Patients between 24 and 34 weeks gestation with documented preterm labor were randomly assigned to receive transdermal GTN (n=24) or intravenous ritodrine (n=35) as initial tocolytic therapy. Patients in the GTN group were administered 0.2 mg/h released transdermal patch on the pregnant women’s abdomen directly. Patient in the ritodrine group were treated 0.025 mg/min as initial dose. The dose increased at 15 minute intervals until uterine contractions were inhibited or side effects become intolerable. The maximum recommended dose was 0.20 mg/min. The main outcome examined were failure of tocolysis, time to uterine quiescence, time gained in utero, and frequency of adverse effects. We obtained both right and left uterine artery doppler velocity waveform before and after tocolytics therapy. The mean values of the right and left uterine artery systolic and diastolic ratio were calculated and used for analysis.
Results: There were no significant difference in maternal demographic between the groups. Successful tocolysis was observed in 79.2% in the GTN group, and 85.7% in the ritodrine group (p=0.726). Time to uterine stop contraction was 5.5 +/- 5.3 hr in ritodrine group and 1.1 +/- 0.3 hr in GTN group. There were no different in time to gain in uterus between the two groups. The patient in the ritodrine group had more adverse side effects, mainly maternal tachycardia (p=0.002), chest pain and tremor (p=0.035). There was no significant difference in uterine S/D ratios between the pretherapy and posttherapy GTN group. However, we found statistically significant difference between the pretherapy and 24 hr-posttherapy in ritodrine group.
Conclusion: Transdermal GTN was effective, safe, and well tolerable tocolytic agent. Patients who received ritodrine hydrochloride were more likely to have adverse effects. We also conclude that GTN do not affect uteroplacental circulations as measured by S/D ratios but ritodrine does. This results suggest that progressively increasing dose of ritodrin and GTN maybe associated with a statistically significant decrease S/D ratios. However, further investigations needs to be performed.
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