Updated 6/5/99
Terbutaline (also known as Brethine) is an asthma drug in the class of drugs known as beta-adrenergics (or beta-sympathomimetics). The only beta-adrenergic that has been approved by the Food and Drug Administration for treating preterm labor is ritodrine. It has since been taken off the market by its manufacturer. However, terbutaline, which was introduced in 1974, often is used "off label" for this purpose as well. This "off label" use continues to occur although terbutaline's manufacturer changed its labeling in 1988 to say it is not approved for use in treating preterm labor. ("Monitoring a High-Risk Pregnancy," March 1992, FDA) Full text of FDA article.
Terbutaline is considered on a milligram to milligram basis to be 35 times more potent than ritodrine (Critical Care Obstetrics, 2nd Ed., Oxford, 1991, pp. 223-250). Terbutaline is usually prescribed in 2.5 or 5.0 mg pills (at 3-, 4-, or 6-hour intervals) or through a subcutaneous pump.
The pump dosages can vary. In general, most women take at least a total of 3 mg per 24 hours. Typically, this 3+ mg is doled out in a low continuous dose of .05 to .09 mg per hour plus boluses (or bigger doses) of about .25 mg at regular intervals (every three to four hours).
The distinction between the pill and subcutaneous pump forms of terbutaline is that the pump dosages are lower, but more concentrated. Thus, even though the pump dosage is lower than the pill form, it is directly absorbed into the blood stream and achieves the same intermittant serum levels as the pill form. The pump also allows for extra dosages of terbutaline to be given when, for example, a woman is having more contractions than her threshhold level. In my own case, I also was directed to take extra doses of terbutaline when I had a doctor's appointment or ultrasound. FDA quote on terb pump's safety
The maximum dose of oral terbutaline for asthmatics is 15 mg per 24-hour period (The Essential Guide to Prescription Drugs, 1998). However, women experiencing preterm labor will take terbutaline around-the-clock and often in significantly higher doses. At a dose of 5 mg every six hours, a woman is taking a total of 20 mg per 24 hour period, or 33% more than this maximum dose for asthmatics. At 5 mg every 4 hours, she is taking 30 mg per 24-hour period, or double the maximum dose for asthmatics. Sometimes the dosages of terbutaline for preterm labor can be even higher than 30 mg.
Some women run a higher risk of serious complications when taking a beta-adrenergic like terbutaline. Risk factors include: underlying heart disease, diabetes, pre-eclampsia, twin pregnancy, combination of terbutaline with corticosteroids and certain other drugs, and fluid overload (The British Journal of Clinical Practice, 1981, Vol. 35, pp. 325-9).
The following is a list of
maternal side effects of beta-adrenergic drugs:
Physiologic:
SOURCES:
- Clinical Obstetrics and Gynecology (1995), Vol. 38, No. 4, pp. 725-727
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