Efficacy and safety of SHR8554 on postoperative pain in subjects with moderate to severe acute pain following orthopedic surgery: A multicenter, randomized, double-blind, dose-explored, active-controlled, phase II/III clinical trial

Biased µ-opioid receptor (MOR) agonists enhance pain relief by selectively activating G protein-coupled receptor signaling and minimizing β-arrestin-2 activation, resulting in fewer side effects. This multicenter Phase II/III trial evaluated the optimal dosage, efficacy, and safety of SHR8554, a biased MOR agonist, for postoperative pain management following orthopedic surgery. In Phase II, 121 patients were divided into four groups to receive varying patient-controlled analgesia (PCA) doses of SHR8554 or morphine. Phase III involved 320 patients with similar groupings, including a placebo group. The primary outcome was the resting summed pain intensity difference over 24 hours (rSPID24). Secondary outcomes included rSPID and active-SPID (aSPID) at other time points, rescue analgesia received, cumulative dose of analgesics, and satisfaction scores. Safety endpoints included treatment-emergent adverse events (TEAEs) and AE of special interest (AESIs). In both phases, SHR8554 demonstrated significant analgesic efficacy. In Phase II, the least squares (LS) mean differences in rSPID24 compared to morphine for the 0.05 mg,0.1 mg, and 0.2 mg SHR8554 groups were 16.8 (p = 0.01), 7.4 (p = 0.27), and 0.2 (p = 0.98), respectively. Phase III confirmed the efficacy of the 0.05 mg and 0.1 mg SHR8554 doses compared to placebo, with LS mean differences of 15.4 (p = 0.0001) and −19.8 (p