Heart drug may improve preterm labor outcomes

Treatment with transdermal nitroglycerin can prolong pregnancy in women who go into labor prematurely and its use seems to reduce illness in the newborn, a study shows.

While a number of drugs called tocolytics that block uterine contractions can prolong pregnancy, “none have been shown to improve neonatal outcomes,” lead author Dr. Graeme N. Smith, from the Kingston General Hospital in Canada, told Reuters Health.

Nitroglycerin is thought to prolong pregnancy by relaxing the uterine smooth muscles, Smith explained. “We used transdermal nitroglycerin off-label, since its approved use is for coronary disease.” However, he added that prior studies have already established a dose of transdermal nitroglycerin that is safe for use during pregnancy.

The study included 153 women who were in labor between 24 and 32 weeks gestation and were randomized to receive transdermal nitroglycerin or placebo.

The use of transdermal nitroglycerin reduced the risk of premature birth before 28 weeks by 50 percent, the report indicates.

Eleven infants in the placebo group experienced the main outcome—a composite of chronic lung disease, inflammation of the intestines, intraventricular hemorrhage, and a brain disorder called periventricular leukomalacia—compared with just three infants in the nitroglycerin.

Moreover, no infant deaths were seen in the nitroglycerin group, while three occurred in the control group.

Women treated with nitroglycerin were 41 percent more likely to experience side effects than were control subjects. Common side effects seen more often with nitroglycerin included headache and local irritation.

Exactly how nitroglycerin improves preterm labor outcomes is unclear, but it may involve more than simply prolonging pregnancy, Smith said. “Nitroglycerin might improve blood flow to the uterus and the placenta,” he speculated.

Since this study was completed, he said that transdermal nitroglycerin has become a standard therapy for preterm labor at his and many surrounding centers.

SOURCE: American Journal of Obstetrics and Gynecology, January 2007.

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