What Is a Tocolytic Drug?

Tocolytic Drugs for Stalling Preterm Delivery

A pregnant woman receives drugs via an IV.
A pregnant woman receives drugs via an IV. Holly Hildreth/Getty Images

A tocolytic drug is a medication that can inhibit labor by reducing or stopping uterine contractions. Tocolytic agents are used widely in medical practice to stall premature labor.

After bedrest, hydration and other less invasive interventions have been tried and have failed, tocolytic therapy may be appropriate and contribute to improved fetal outcomes. While these drugs are rarely successful in achieving delays long enough to allow a fetus to make significant gains in weight and development, they are often successful in stopping labor for 24 to 48 hours.

That delay is considered a critical window of opportunity during which doctors can administer corticosteroid drugs. These drugs, when given as close as 12 to 24 hours before deliver, can significantly speed up fetal lung development and reduce the likelihood of neonatal respiratory distress syndrome, intraventricular hemorrhage and death.

In addition, a delay in delivery of only hours can allow pregnant women to be transferred to medical centers with expertise and facilities more suitable for premature deliveries and neonatal intensive care units.

Types of Tocolytic Drugs

There is no data that shows any of the tocolytic drugs are more effective than the others, however each of them has a different safety profile with regards to both the mother and the fetus. Which drug is chosen should depend on individual factors such as health of the mother, potential side effects and gestational age of the fetus.

The most common tocolytics used to treat preterm labor include:

  • Magnesium sulfate (MgSO4): In use since 1969 and the most commonly used tocolytic agent today.

  • Indomethacin: A prostaglandin inhibitor, this drug has fewer side effects than Ritodrine and Terbutaline (drugs no longer in use because of their risks) but still carries some significant risks to both mother and fetus.

  • Ritodrine: The only drug approved by the FDA as a tocolytic, this drug carries the risk of serious maternal cardiopulmonary and metabolic complications such as hyperglycemia.

  • Nifedipine: This drug can be administered orally, and can be rapidly absorbed.

The best candidates for tocolytic therapy are women who:

  • Are between 24 and 34 weeks gestation
  • Are less than 4 cm dilated

Who Should Not Use Tocolytic Drugs?

Women and their physicians should carefully weigh the benefits of any medical intervention against the risks they pose to either themselves or their fetuses. Generally, the risks of tocolytics outweigh the benefits for women with severe preeclampsia or eclampsia (high blood pressure that develops during pregnancy), severe bleeding (hemorrhage), or infection in the womb (chorioamnionitis)

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