Current perspectives on drug treatment for preterm labour

The effects of oxytocin and atosiban on the modulation of heart rate in pregnant women

OBJECTIVE

To evaluate autonomic modulation of heart rate in pregnant women treated with oxytocin to induce labor and with atosiban (an oxytocin antagonist) to arrest preterm labor.

METHODS

A prospective study with two cohorts: 14 pregnant women treated with atosiban for premature uterine contractions, and 28 women undergoing induction of labor with oxytocin. Computerized analyses of the electrocardiogram were performed with spectral and nonlinear dynamic analyses.

RESULTS

Atosiban did not alter any of the variables associated with heart rate variability, whereas oxytocin showed a dose-dependent decrease in heart rate (p < 0.05) and a significant increase in all spectral variables studied (p < 0.01).

CONCLUSIONS

Atosiban has no adverse effects on the cardiovascular system or the modulation of heart rate. Oxytocin, on the other hand, can cause a dose-dependent bradycardic effect and an increase in the spectral power, thus should be used with caution in certain pregnant women.

Treatment of preterm labor with the oxytocin antagonist atosiban: a double-blind, randomized, controlled comparison with salbutamol

OBJECTIVE

To compare the efficacy and safety of atosiban and salbutamol in the treatment of preterm labor.

STUDY DESIGN

A multicenter, double-blind, double-placebo, randomized, controlled trial. Women (n=241) diagnosed with preterm labor at 23-33 gestational weeks were enrolled and received either atosiban (n=119) or salbutamol (n=122). At randomization, women were stratified by gestational age (< or =28 weeks and >28 weeks). Atosiban (i.v. bolus dose of 6.75 mg, then 300 microg/min for 3h and 100 microg/min for up to 48h) and salbutamol (2.5-45 microg/min) were administered by i.v. infusion for up to 48h. Retreatment with study drug or an alternative tocolytic agent was allowed. Main outcome measures included tocolytic effectiveness which was assessed in terms of the number of women undelivered after 48h and 7 days. Tocolytic efficacy and tolerability were assessed in terms of the proportion of women undelivered and who did not require alternative tocolytic therapy at 48h and 7 days of starting treatment. Safety was assessed in terms of maternal side effects and neonatal morbidity.

RESULTS

Tocolytic effectiveness at 48h was 93.3 versus 95.0% (P=0.67) and after 7 days was 89.9 versus 90.1% (P=0.93) in the atosiban and salbutamol groups, respectively. Tocolytic efficacy and tolerability within 48h was 79.8 versus 75.2% (P=0.15), and after 7 days was 58.8 versus 46.3% (P=0.021) in the atosiban and salbutamol groups, respectively. Maternal adverse events, including serious events, occurred more frequently in the salbutamol group. Neonatal outcomes were comparable between the study groups.

CONCLUSIONS

The oxytocin antagonist atosiban was found to be better tolerated by both mother and fetus than salbutamol, with a comparable neonatal and infant safety profile, and atosiban was as effective as salbutamol in delaying threatened preterm birth. This study supports the clinical use of atosiban in the treatment of preterm labor.

Double-blind, randomized, controlled trial of atosiban and ritodrine in the treatment of preterm labor: a multicenter effectiveness and safety study

OBJECTIVE

This study was undertaken to compare the efficacy and safety of intravenous administration of atosiban versus ritodrine for the treatment of preterm labor.

STUDY DESIGN

Women with preterm labor and intact membranes diagnosed at 23 to 33 gestational weeks (n = 247) were randomly assigned to treatment arms and received atosiban (6.75 mg intravenous bolus, 300 microg/min for 3 hours, then 100 microg/min intravenously) or ritodrine (0.10-0.35 mg/min intravenously) for as long as 18 hours. Tocolytic effectiveness was assessed in terms of the numbers of women who had not been delivered after 48 hours and after 7 days. Safety was assessed in terms of maternal side effects and neonatal morbidity. Secondary outcomes included mean gestational age at delivery and mean birth weight. An intent-to-treat analysis was performed with the Cochran-Mantel-Haenszel test.

RESULTS

The proportion of women who had not been delivered at 48 hours was 84.9% (n = 107) in the atosiban group and 86.8% (n = 105) in the ritodrine group. At 7 days 92 women had still not been delivered in both the atosiban (73.0%) and ritodrine (76.0%) groups. Neither of these differences was statistically significant. The incidence of maternal cardiovascular side effects was substantially lower in the atosiban group (4.0% vs 84.3%, P <.001). In addition, intravenous therapy was terminated more frequently as a result of maternal adverse events in the ritodrine group (29.8%) than in the atosiban group (0.8%). The overall occurrences of fetal adverse events in the two treatment groups were comparable. Neonatal morbidity was similar between the treatment groups after adjustment for unbalanced enrollment of women with multiple pregnancies and for gestational ages within treatment groups.

CONCLUSION

Atosiban was comparable in clinical effectiveness to conventional ritodrine therapy but was better tolerated than ritodrine, with no evidence of significant maternal or fetal adverse events. Neonatal morbidity, which was similar between the two treatment arms, was apparently related to the gestational age of the infant rather than to the exposure to either tocolytic agent.