Comparison of Postoperative Analgesic Efficacy of Two Intrathecal Morphine Doses (75 μg vs 100 μg) for Cesarean Delivery: A Double-Blind Randomized Study

BACKGROUND: Intrathecal morphine remains a cornerstone of post-cesarean analgesia due to its prolonged spinal effect; however, its use is limited by dose-dependent adverse effects. Contemporary practice trends favor dose minimization, yet the lowest dose that reliably maintains effective analgesia remains unclear. This study aimed to evaluate whether a reduced dose of 75 μg provides analgesic efficacy comparable to a standard 100 μg dose. METHODS: In this prospective, randomized, double-blind trial, 240 ASA II women undergoing elective cesarean delivery under spinal anesthesia were allocated to receive either 75 μg or 100 μg of preservative-free intrathecal morphine combined with 7.5 mg of 0.5% isobaric bupivacaine. Postoperative pain intensity was assessed using the Visual Analog Scale (VAS, 0-10) at 0, 4, 8, 12, and 24 hours. Secondary outcomes included rescue analgesic requirements, maternal adverse effects, and neonatal Apgar scores. RESULTS: All 240 enrolled participants completed the study protocol. At the primary 12-hour endpoint, pain intensity did not differ significantly between groups, with median VAS scores of 0.0 (IQR 1.0) in the 75 μg group and 1.0 (IQR 1.75) in the 100 μg group (p = 0.224); no significant differences were observed at 4, 8, or 24 hours. Non-opioid rescue analgesia was required in 50/120 (41.7%) patients in the 75 μg group and 45/120 (37.5%) in the 100 μg group (p = 0.509), with no patients requiring opioid rescue. Maternal adverse effects were comparable between groups, including pruritus in 30/120 (25.0%) patients in the 75 μg group and 25/120 (20.8%) in the 100 μg group (p = 0.442), and nausea in 20/120 (16.7%) and 10/120 (8.3%) patients, respectively (p = 0.051). Neonatal outcomes were favorable, with all neonates achieving Apgar scores ≥8 at five minutes. Although statistically significant differences were observed between groups, these differences were not clinically meaningful. CONCLUSIONS: A 75 μg dose of intrathecal morphine was associated with comparable 24-hour postoperative analgesia to 100 μg, with no statistically significant differences observed between groups in pain scores or adverse effects. These findings suggest that lower doses may provide adequate analgesia while maintaining a similar safety profile. However, further studies specifically designed as non-inferiority or equivalence trials are required to confirm these observations.