Oxytocin antagonists are used as tocolytics in preterm labor. Which among the following is an oxytocin antagonist?
**Core Concept**
Oxytocin antagonists are a class of medications used to inhibit uterine contractions in preterm labor. They work by blocking the action of oxytocin, a hormone that stimulates uterine contractions. Oxytocin antagonists are a type of tocolytic agent, which are used to delay preterm birth and allow for further fetal maturation.
**Why the Correct Answer is Right**
Atosiban is a selective oxytocin receptor antagonist that blocks the action of oxytocin on the uterine muscle. By inhibiting oxytocin receptors, atosiban reduces the frequency and intensity of uterine contractions, thereby delaying preterm labor. Atosiban is a synthetic peptide that mimics the action of oxytocin, but with a reversed effect.
**Why Each Wrong Option is Incorrect**
**Option A:** Nifedipine is a calcium channel blocker that is used as a tocolytic agent, but it works by relaxing the uterine muscle through a different mechanism than oxytocin antagonism.
**Option B:** Ritodrine is a beta-2 adrenergic agonist that is used as a tocolytic agent, but it works by stimulating the uterine muscle to relax, rather than blocking oxytocin receptors.
**Option C:** Magnesium sulfate is a tocolytic agent that is used to relax the uterine muscle, but it works by inhibiting calcium influx, rather than blocking oxytocin receptors.
**Clinical Pearl / High-Yield Fact**
Oxytocin antagonists like atosiban are a useful option for tocolysis in preterm labor, as they can delay birth without the side effects associated with other tocolytic agents.
**Correct Answer:** C. Atosiban.