Inadequate postoperative pain management can lead to physical and psychological distress in patients as well as impact surgical wound healing and increase the risk of developing postoperative delirium and cardiopulmonary and thromboembolic events. Severe postoperative pain may also result in the development of chronic post-surgical pain (CPSP), which in turn can lead to prolonged use of opioids and increased health-care costs. A descriptive survey study in 60 postpartum women who received cesarean section suggested that the presence of postoperative pain significantly reduced the willingness of breastfeeding and infant care. Furthermore, the incidence of CPSP after cesarean delivery has been reported to vary from 1% to 18% up to 1 year after operation. More specifically, an US nationwide survey reported that 79% of mothers who received cesarean section reported experiencing pain at the incision site in the first two months and 18% had persistent pain at least 6 months after operation. Placement of an epidural catheter can be used for epidural anesthesia during cesarean section and continuous epidural infusions of opioids or combined with local anesthetic after cesarean section can result in high-quality analgesia effect for postpartum and postsurgical pain. Intrathecal injection of morphine (ITM) is considered as the standard pain management strategies for post-cesarean pain in Taiwan. However, correct placement of epidural catheter for effective postoperative pain management is more technical demanding, and accidental dural puncture is associated with increased risk of postdural puncture headache. ITM is associated with severe mu-receptor agonist adverse reactions, such as pruritus, nausea/vomiting, urinary retention, constipation, mental status change, and respiratory depression. Therefore, the development of a safe, conveniently operated, and long-lasting non-mu agonism analgesic strategy, which serves as background pain control modality up to several days after cesarean section should provide clinically beneficial advantages in the management of acute postoperative pain and prevention of development of CPSP in postpartum women.

Sebacoyl dinalbuphine ester Naldebain® (SDE) is prodrug of nalbuphine, which was approved by the Taiwan FDA in 2017. SDE is rapidly hydrolyzed by tissue of plasma esterase to release nalbuphine. The bioavailability of nalbuphine following intramuscular injection SDE was 85.4% with a mean absorption time up to 145 h, and it took approximately 6 days for the complete release of SDE into the blood circulation. Therefore, a single parenteral injection of SDE could provide long lasting analgesic effect in several phase II trials. However, SDE has not been tested in the pain control after cesarean section. Therefore, this PI-initiated prospective, randomized, open-label, non-inferiority trial aims to investigate the clinical efficacy of SDE in management of acute postoperative pain in term parturient who receive elective cesarean section to provide analgesic effect that is not inferior to the standard ITM. A single intramuscular injection of SDE may also prevent the development of CPSP after cesarean delivery, as SDE can provide prolonged analgesic effect for up to 7 days.