AbstractBackgroundSTARDOM2 is a randomized, double‐blind, phase 3 trial evaluating the efficacy and safety of co‐crystal of tramadol‐celecoxib (CTC)—a first‐in‐class analgesic co‐crystal comprising racemic tramadol hydrochloride and celecoxib in a supramolecular network that modifies their pharmacokinetic properties—for the management of acute postoperative pain (NCT03062644; EudraCT:2016–000593‐38).MethodsPatients with moderate‐to‐severe pain following abdominal hysterectomy were randomized 2:2:2:2:2:1 to oral CTC 100 mg (rac‐tramadol hydrochloride 44 mg/celecoxib 56 mg) twice daily (BID); CTC 150 mg (66/84 mg) BID; CTC 200 mg (88/112 mg) BID; immediate‐release tramadol 100 mg four times daily (QID); celecoxib 100 mg BID; or placebo, for 5 days. The primary endpoint was the sum of pain intensity differences over 0–4 h (SPID_0–4). Key secondary endpoints were rescue medication use within 4 h, 50% response rate at 4 h, and safety/tolerability.ResultsOf 1355 patients enrolled, 1138 were randomized (full analysis set) and 1136 treated (safety analysis set). In the prespecified gatekeeping analysis of SPID_0–4, CTC 200 mg was not superior to tramadol but showed non‐inferior efficacy (p < 0.001) that was sustained throughout the 120‐h period, despite a 5‐day cumulative tramadol administration of 880 mg with CTC 200 mg BID versus 2000 mg with tramadol 100 mg QID. Treatment‐emergent adverse events (TEAEs) and severe TEAEs were less common with CTC 200 mg versus tramadol. Treatment‐related TEAEs were 14.4% with CTC 200 mg and 23.6% with tramadol.ConclusionsAlthough the study did not meet its primary endpoint, CTC 200 mg showed a clinically relevant improvement in overall benefit/risk profile versus tramadol alone, with considerably lower cumulative opioid exposure.SignificanceIn the randomized, double‐blind, phase 3 STARDOM2 trial—in acute moderate‐to‐severe pain after abdominal hysterectomy—the novel co‐crystal of tramadol‐celecoxib (CTC) 200 mg BID was superior to placebo and non‐inferior to tramadol 100 mg QID. Although superiority to tramadol was not reached, CTC 200 mg BID exposed patients to lower cumulative opioid (tramadol) doses than tramadol (100 mg QID) alone, with fewer treatment‐emergent adverse events. CTC 200 mg thus has a clinically relevant improved benefit/risk profile compared with tramadol alone.