Delaying premature labor with nifedipine

Last updated: November 2010

Most pregnancies last about 40 weeks, but about one in eight births in the U.S. occur before the 37th week, when the fetus is not fully developed. Those preterm babies are more likely to have serious illnesses or die than full-term babies, and they're at higher risk for learning and developmental disabilities.

Doctors can treat women in preterm labor with medicines known as tocolytics, which might slow down or inhibit labor for two to seven days. That buys enough time for them to receive corticosteroid drugs, which might help avoid complications of a preterm birth. If given at least 24 hours before birth, corticosteroids can help prevent some of the worst problems a premature baby faces, such as a severe lung disease called respiratory distress syndrome; bleeding in the brain; and a serious bowel disease called necrotizing enterocolitis. The two-to-seven-day window afforded by tocolytics might also be enough time to transfer the mother to a hospital equipped with a neonatal intensive care unit (NICU), which has staff members and specialized equipment to help increase the newborn's chance of survival.

No approved drug for halting contractions is currently available in the U.S., so any medication prescribed for this purpose is used off-label. But some tocolytic drugs can produce side effects for the mother, the fetus or both, and several have been serious. That's why obstetricians have a growing interest in nifedipine (Adalat, Procardia, and generics), a medicine that appears to cause fewer side effects than some other tocolytics, although it has been found to also produce some serious adverse effects. Nifedipine is approved to control high blood pressure and angina (chest pain). Classified as a calcium-channel blocker, nifedipine blocks the passage of calcium into cardiac and smooth muscle, like those of the uterus. And calcium is needed for the uterus to contract. Nifedipine is one of the most widely used and studied medications among the calcium-channel blockers to suppress preterm contractions.

But the use of tocolytics is controversial. In 80 percent of women with suspected preterm labor, early delivery will not occur. Yet there is no reliable test to determine which women are experiencing "true" or "false" preterm labor, so some are treated with medication unnecessarily. Moreover, the American College of Obstetricians and Gynecologists (ACOG) cautions that tocolytics have demonstrated only limited benefit.

"Tocolytics haven't been able to prolong pregnancy," says Michael G. Ross, M.D., M.P.H., chairman of the obstetrics and gynecology department at Harbor-University of California Los Angeles Medical Center. "At most they will delay delivery for 48 hours so we can administer steroids to the mother. Nifedipine appears to be as effective as the other tocolytic drugs in that regard and is probably a drop safer."

What is the evidence for the use of nifedipine for preterm labor?

More than 40 studies have been published on nifedipine's effectiveness as a tocolytic. In the available literature reviewed to date, according to an analysis prepared by the American Society of Health-System Pharmacists, no well-designed placebo comparison or double-blind trials of nifedipine have been conducted. And most included small samples and had other shortcomings that made it difficult to assess outcomes.

A 2003 Cochrane analysis combined evidence from 12 randomized controlled trials involving 1,029 women. When compared with other tocolytic drugs-mainly a group of drugs called betamimetics, which have safety concerns but have been widely-tested-calcium-channel blockers, usually nifedipine, reduced the number of women giving birth within seven days of treatment and before 34 weeks of pregnancy. In addition, calcium-channel blockers were associated with fewer women discontinuing treatment because of side effects. The babies whose mothers received calcium-channel blockers were less likely to develop respiratory distress syndrome, bleeding in the brain, serious bowel disease, and jaundice.

While nifedipine fared well in the Cochran analysis, there were more than three dozen studies that were not included and that will eventually be added. They could change the final conclusion of the review. In the meantime, according to ASHP, there is insufficient evidence to fully compare nifedipine with other tocolytics or understand the ideal dosing regimen and best form of the medication to take. More research is needed.

What are the risks with nifedipine for preterm labor?

While calcium-channel blockers appear to have a good maternal and fetal safety profile, most studies on tocolytic drugs have primarily focused on otherwise low-risk pregnancies. No fetal side effects have been noted with calcium-channel blockers, according to ACOG's practice guidelines (May, 2003).

But nifedipine is associated with an increased risk of angina, heart attack, congestive heart failure, irregular heart rhythm, oxygen deficiency in the tissues (hypoxia), and renal failure.

And the following maternal and general risks have been reported:

Hypotension (abnormally low blood pressure). In a European study that recorded serious maternal complications with tocolytic drugs, the most frequent and troubling one concerning women taking nifedipine was hypotension. But the authors questioned the importance of that complication because it did not appear to affect the fetus.

Dyspnoea (difficult or labored breathing and shortness of breath). A Dutch medical center reported seven cases of severe dyspnoea in which tocolytic treatment with nifedipine was the suspected cause (or at least could not be excluded). In all cases the drug was stopped and the women recovered rapidly. Six of the seven women were carrying twins.

Peripheral edema (buildup of fluid in the ankles, feet and legs). Mild to moderate swelling might occur in about 10 percent of people taking nifedipine.

Drug interactions. Nifedipine has been found to interact with beta-blockers and other medication including digoxin (Cardoxin, Digitek, Lanoxicaps, Lanoxin), quinidine, warfarin (Coumadin), cimetidine (Tagamet), and magnesium sulfate.

Food interactions. Avoid eating grapefruit or drinking grapefruit juice for three days before taking nifedipine and while taking it.

Common side effects. They include headaches, nausea, dizziness, flushing, a fast heartbeat, muscle cramps, constipation, and coughing.

Who should be cautious about using a tocolytic drug? Side effects and other complications might be higher in women with a multiple pregnancy, a preterm rupture of the membranes, vaginal bleeding, an infection within the uterus, diabetes, or a history of heart disease. Using more than one tocolytic drug, either combined or sequentially, might be harmful to the mother.

"In addition, some doctors treat women with nifedipine or other tocolytic drugs for a longer time to attempt to prevent a future episode of premature labor," says Jay Iams, M.D., the Frederick P. Zuspan Professor and endowed chairman in the division of maternal fetal medicine at Ohio State University. "But once you've accomplished steroid administration and transferred the mother, longer use of tocolytics has no apparent benefit." Guidelines from ACOG warns that prolonged use might potentially increase maternal-fetal risk without offering a clear benefit.

What steps can you take to handle preterm labor?

Don't overreact. False labor—also known as Braxton Hicks contractions—is common in the last trimester of pregnancy and usually goes away in an hour or so with rest. "Place your fingers on your tummy and feel the muscle tighten, and write down the frequency of your contractions," Ross advises.

Call your doctor right away if you have any of the following signs of preterm labor:

  • Four contractions every 20 minutes, or regular or frequent contractions or uterine tightening.
  • A change in vaginal discharge (watery, mucus or bloody) or increased discharge.
  • Pelvic or lower abdominal pressure that might feel as if the baby is pushing down low, or a dull backache.
  • Mild abdominal cramps with or without diarrhea, or cramps similar to what you might experience during your period.
  • A ruptured membrane (your water breaks with a gush or trickle).

Your doctor might examine you to see if your cervix has thinned and dilated, because those changes indicate preterm labor. He or she might also measure your cervix using ultrasound and do a test to detect a cervical secretion known as fetal fibronectin. Those tests can help predict your risk of preterm birth and can prevent unnecessary intervention if they show reduced risk.

If early delivery is probable, it might be delayed briefly with a tocolytic drug-especially if you are between 24 and 34 weeks of pregnancy, when steroids are most likely to help your baby. No tocolytic drug should be used when labor is too far along or if the mother and fetus are in danger from infection, bleeding, or other complications.

Bottom line. Nifedipine and other tocolytic drugs might stop preterm labor for two to seven days, providing time to use corticosteroids to help reduce complications in the fetus associated with preterm delivery and to transport the mother to a hospital with a NICU. There is no clear first-line tocolytic drug to manage preterm labor, so the choice depends on the situation.

Our advice: Talk with your doctor about all available options for preterm labor, and consider nifedipine only after its risks and benefits have been thoroughly explained to you.

This off-label drug use report is made possible through a collaboration between Consumer Reports Best Buy Drugs and the American Society of Health-System Pharmacists. This is the17th in a series based on professional reports prepared by ASHP.

These materials were made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by a multistate settlement of consumer fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).

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