The Use of Tocolytic Agents For Premature Labor

Posted on May 27, 2012

When a woman goes into preterm labor, many doctors look for ways to delay the delivery, even if only for a day or two. This allows them to transport the mother to a medical center with a neonatal intensive care unit (NICU) if necessary, or to inject antenatal corticosteroids, to help mature an infant’s lungs. In order to do this, doctors may administer tocolytic medicines, which can slow down contractions and delay labor in women who have reached their 24th week of pregnancy.

There are four types of tocolytic medicines: Terbutaline, magnesium sulfate, Indomethacin, and Nifedipine (a type of calcium channel blocker). Use of Terbutaline, the most effective of the tocolytic agents at delaying labor, has waned in recent years as doctors discovered maternal and fetal side effects such as maternal tachycardia, hyperglycemia, and palpitations; the FDA decided that the risk of severe adverse reactions outweighs any benefit to pregnant women from prolonged use of the drug. Now, many doctors use magnesium sulfate as the primary tocolytic agent, because it is nearly as effective as Terbutaline without the adverse side effects. Indomethacin is most effective as a first-line tocolytic for a pregnant mother in very early preterm labor (less than 30 weeks). Nifedipine is a calcium channel blocker, and works by inhibiting contractility in smooth muscle cells by reducing the amount of calcium reaching the cells. Though not as commonly used as the other tocolytic agents, some studies show Nifidepine may be more effective than other tocolytic agents.

The randomized results of controlled trials of tocolytic agents were analyzed in an effort to determine the effect of tocolytic agents on preterm labor. The study showed that all tocolytic agents were much better than placebo or control groups at delaying delivery 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).