A normal pregnancy lasts about 40 weeks. While most pregnant women go into labor at the 40-week mark, some women go into labor earlier. Preterm labor is characterized by uterine contractions that begin to open the cervix before the 37th week of pregnancy.
If preterm labor isn’t stopped, the baby will be born early, or prematurely. Premature babies often need additional care after birth and sometimes have long-term health problems that can affect their entire lives. The earlier in pregnancy a baby is born, the more likely they are to have complications.
Doctors may try to stop or delay preterm labor by administering a medication called terbutaline (Brethine). Terbutaline is in a class of drugs called betamimetics, which help prevent contractions of the uterus. It may help delay birth for several hours or days. During that time period, doctors can administer other drugs to help ensure the baby is born as healthy as possible.
Terbutaline can be given subcutaneously, which means injected into the skin, or intravenously (IV), which means given through a vein. The usual dose of terbutaline is 0.25 milligrams. It’s usually injected into the shoulder or given through a vein in the arm. A second dose of 0.25 milligrams may be administered if there isn’t a significant decrease in contractions within 15 to 30 minutes. If the second dose isn’t effective, other treatments will be considered. The total dose of terbutaline shouldn’t exceed 0.5 milligrams, and the medication shouldn’t be used for more than two days at a time.
A new way of getting terbutaline, which is through the continuous subcutaneous infusion pump, allows the medication to be administered easily without the need for an IV. However, there are disadvantages associated with the pump. It’s expensive and more invasive than the subcutaneous route. Also, since there have been only a few small studies on use of the pump, it isn’t clear how effective it is for treating preterm labor.
Terbutaline used to be prescribed as an oral medication, but this form of the drug was discontinued due to dangerous side effects and safety concerns. Oral terbutaline shouldn’t be taken any longer.
It’s also important to note that terbutaline should never be used outside of a hospital. The drug is only supposed to be administered in hospital settings with medical staff available.
How it Works
Terbutaline is derived from a hormone called epinephrine, which is released when someone is under stress. This response is commonly called the fight-or-flight response. Stress causes many of the muscles in the body to contract, so that a person is ready to respond quickly. However, there are certain muscles that relax instead of contracting during times of stress. Smooth muscle is one type of muscle that relaxes when someone is under stress. Since most of a woman’s uterus is made up of smooth muscle, the uterus will relax in response to a drug that contains certain substances, such as epinephrine.
Women respond differently to terbutaline, so its effects and how long they last vary from one woman to another. When you have a good response to terbutaline, the drug reduces the number and frequency of contractions. This can help delay delivery for several hours, depending on how quickly the medication is received.
Although this may not seem like a lot of time, when terbutaline is administered along with steroids, it can significantly lower the risk for health problems in the baby. After 48 hours, steroids can improve a baby's lung function and increase their chances of living by 40 percent.
The use of terbutaline may be successful in treating preterm labor. However, it does come with some risks to the mother and the baby.
For the Mother
Since terbutaline is related to hormones released in the fight-or-flight response, a woman may experience the same effects when taking terbutaline as she does when under stress. Many women experience:
- a racing heartbeat
A few women have more serious side effects, such as irregular heartbeats, extra fluid in the lungs, which is called pulmonary edema, and chest pain. The more serious side effects tend to occur when women are taking high doses, but the effects can also occur with standard doses. Terbutaline may also increase your risk of diabetes.
For the Baby
Terbutaline can cause a temporary increase in the baby’s heart rate and blood sugar levels. These side effects usually aren’t serious and are easy to treat after delivery if they occur.
Women who have medical conditions that could be aggravated by the possible side effects of terbutaline shouldn’t take the drug. This includes women with heart disease, hyperthyroidism, and poorly controlled diabetes.
The FDA issued an advisory in February of 2011 regarding the use of terbutaline in the treatment of preterm labor. This warning was specific to the “off-label” use of terbutaline to treat preterm labor. The warning says that the oral form of the drug should never be used to treat preterm labor because it doesn’t work. It also warns that injectable terbutaline should only be used in urgent situations and for no longer than 48 to 72 hours. Prolonged use of the medication greatly increases the risk for life-threatening heart problems in the mother.
It’s important to be aware of this warning, but specific situations may result in this drug being used by specialists for longer periods under close supervision. Talk to your doctor if you have any concerns.