Why is it that older non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or indomethacin, not newer NSAIDs, such as etoricoxib, are used to promote closure of patent ductus arteriosus in preterm infants?

In the fetus, the ductus arteriosus acts as a lung bypass diverting blood from the pulmonary artery into the aorta.  After birth, the ductus arteriosus constricts and is eventually obliterated. In preterm births, the ductus arteriosus may remain patent resulting in insufficient blood flow through the pulmonary circulation and increased risk of mortality.

Prostaglandin E₂ (PGE₂) is a vasodilator promoting patency of the ductus arteriosus. NSAIDs inhibit the cyclooxygenase (COX) enzyme responsible for producing  PGE₂. NSAIDs are therefore contraindicated in the third trimester of pregnancy as they can cause premature closure of the ductus arteriosus in utero. However, in preterm infants, NSAIDs can be valuable in enabling closure of patent ductus arteriosus (PDA).

The NSAIDs used are typically ibuprofen or indomethacin. These are older NSAIDs for which there is a longer history of experience with use in infants. Ibuprofen is generally the preferred agent as it has a lower risk of reducing gastrointestinal and renal blood flow resulting in necrotizing enterocolitis and transient renal insufficiency. The newer coxibs, such as etorixocib, are not used because there is less knowledge of their safety in infants.

Reference:

Philips III, JB (2018) Management of patent ductus ateriosus in preterm infants. Garcia-Prats JA, Fulton DR, Kim MS ed. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com (Accessed on October 5, 2018).