What are the most common tocolytic agents used to treat preterm labor?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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The most common tocolytic agents used for the treatment of preterm labor are magnesium sulfate (MgSO4), indomethacin, and nifedipine. In the past, beta-mimetic agents, such as terbutaline or ritodrine, were the agents of choice, but in recent years their use has been significantly curtailed due to maternal and fetal side effects, such as maternal tachycardia, hyperglycemia, and palpitations The use of these agents can lead to pulmonary edema, myocardial ischemia, and cardiac arrhythmia.

In February 2011, the US Food and Drug Administration (FDA) required the addition of a new Black Box Warning and contraindication to the terbutaline prescribing information to warn about the risk of use for preterm labor. The decision was based on reports of death and serious adverse reactions, including tachycardia, transient hyperglycemia, hypokalemia, arrhythmias, pulmonary edema, and myocardial ischemia following prolonged administration of oral or injectable terbutaline to pregnant women. The FDA concluded that the risk of serious adverse events outweighs any potential benefit to pregnant women receiving prolonged treatment with terbutaline injection (>48-72 h) or acute or prolonged treatment with oral terbutaline.

The tocolytic agents currently used to treat preterm labor appear to be equally efficacious in delaying delivery for at least 48 hours. While MgSO4 is associated with more maternal toxicity, indomethacin is associated with more fetal and neonatal toxicity.

Haas et al analyzed randomized controlled trials of tocolysis to determine the optimal first-line tocolytic agent for treatment of premature labor. Fifty-eight studies satisfied the inclusion criteria. A random-effects meta-analysis showed that all tocolytic agents were superior to placebo or control groups at delaying delivery both for at least 48 hours (53% for placebo compared with 75-93% for tocolytics) and 7 days (39% for placebo compared with 61-78% for tocolytics). No statistically significant differences were found for the other outcomes, including the neonatal outcomes of respiratory distress and neonatal survival. The decision model demonstrated that prostaglandin inhibitors provided the best combination of tolerance and delayed delivery. [31]

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