Which of the following medications will be administered to assist with closure of patent ductus arteriosus (PDA) in premature infants?

Choice A rationale Terbutaline is a β_2-adrenergic receptor agonist primarily used as a tocolytic agent to suppress premature labor by relaxing the uterine smooth muscle. It may also be used as a bronchodilator. It does not exert the necessary prostaglandin synthesis inhibition required to cause vasoconstriction and eventual anatomical closure of a patent ductus arteriosus (PDA) which is mediated through different physiological pathways. Its mechanism is unrelated to PDA management. Choice B rationale Betamethasone is a corticosteroid typically administered prenatally to mothers at risk of preterm delivery. Its primary function is to accelerate fetal lung maturation by stimulating the production of pulmonary surfactant, thereby reducing the incidence and severity of respiratory distress syndrome (RDS). It is not directly used postnatally in the infant to pharmacologically close a patent ductus arteriosus (PDA) through prostaglandin pathway inhibition. Choice C rationale Methotrexate is an antimetabolite and folate antagonist used primarily as a chemotherapeutic agent and an immunosuppressant for conditions like cancer and severe autoimmune diseases. Its mechanism of action involves interfering with DNA synthesis, which is not the targeted physiologic mechanism for promoting the closure of a patent ductus arteriosus (PDA) in a neonate, as that requires prostaglandin synthesis inhibition. Choice D rationale Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID) that acts as a potent cyclooxygenase (COX) inhibitor, thereby blocking the synthesis of prostaglandins. Prostaglandin E_2 and prostacyclin keep the ductus arteriosus (DA) patent. Inhibiting their production allows for the vasoconstriction and eventual functional and anatomical closure of the DA, which is the desired outcome for patent ductus arteriosus (PDA) closure.