Which medication among the following is a beta-adrenergic agonist used as a tocolytic?

• A. Indomethacin
• B. Nifedipine/Procardia
• C. Magnesium sulfate
• D. Terbutaline

Answer: (D)

Tocolysis with a beta-adrenergic agonist works by activating beta-2 receptors on uterine smooth muscle, which raises cAMP inside the cells and reduces intracellular calcium. This sequence relaxes the uterine muscles and slows or stops contractions, helping to delay preterm labor.

Terbutaline fits this action precisely—it's a beta-2 agonist used clinically to relax the uterus during preterm labor. The other medications use different mechanisms: indomethacin lowers contractions by inhibiting prostaglandin synthesis; nifedipine is a calcium channel blocker that reduces calcium influx into smooth muscle; magnesium sulfate acts as a CNS depressant and interferes with calcium signaling to dampen uterine activity. While all can serve as tocolytics in various settings, they are not beta-adrenergic agonists.

Be mindful of terbutaline’s side effects and monitoring needs—maternal tachycardia, palpitations, and potential hyperglycemia, among others, mean it’s used with close observation and typically for short-term tocolysis.