Which agent is commonly used as a tocolytic to reduce contractions in preterm labor?

• A. Betamethasone
• B. Magnesium sulfate
• C. Penicillin
• D. Nifedipine

Answer: (D)

To reduce uterine contractions in preterm labor, a calcium channel blocker is commonly used. Nifedipine works by blocking L-type calcium channels in uterine smooth muscle, lowering intracellular calcium and causing the uterus to relax. This makes it effective at delaying labor with a relatively favorable safety profile, especially when compared with beta-agonists that can cause tachycardia and other side effects. Betamethasone is given to accelerate fetal lung maturity, not to stop contractions. Penicillin is an antibiotic for infection prophylaxis, not a tocolytic. Magnesium sulfate can be used as a tocolytic in some settings but is often reserved for fetal neuroprotection and seizure prophylaxis, and it generally isn’t the first-line tocolytic. Therefore, the agent most commonly used to suppress contractions is nifedipine.