Which drug can be used as a tocolytic to delay labor by up to 48 hours?

Nifedipine is recognized as an effective tocolytic agent used to delay preterm labor for up to 48 hours. It is a calcium channel blocker that works by relaxing the smooth muscle of the uterus, thereby decreasing uterine contractions. This ability to prolong pregnancy for a short duration can be crucial, especially in situations where interventions such as administering corticosteroids to accelerate fetal lung maturity are needed before delivery.

Magnesium sulfate, while it has tocolytic properties, is primarily used for neuroprotection of the fetus in cases of imminent preterm birth, making it less effective as a sole tocolytic compared to nifedipine. Indomethacin is another tocolytic, but its use is typically limited due to potential risks to the fetus, especially concerning oligohydramnios or premature closure of the ductus arteriosus. Terbutaline can also delay labor, but it is less favored due to more significant side effects and a limit on the duration of its use.

Overall, nifedipine stands out among these options for its efficacy and safety profile in extending pregnancy when immediate intervention is needed.