This randomized, double-blind, placebo-controlled study will evaluate the efficacy and safety of tegileridine fumarate injection for postoperative analgesia in adults experiencing moderate-to-severe pain after abdominal surgery. Participants will be randomized to receive intravenous tegileridine or matching placebo as part of a standardized multimodal analgesia protocol; all patients will have access to rescue opioid analgesia per institutional practice. The primary objective is to determine whether tegileridine improves postoperative pain control during the first 24-48 hours after surgery. Secondary objectives include comparing cumulative opioid consumption, time to first rescue analgesia, patient-reported satisfaction with pain control, recovery milestones (e.g., time to ambulation), and the incidence of adverse events such as nausea, vomiting, sedation, respiratory depression, pruritus, and constipation. Safety will be monitored throughout the study with predefined stopping and reporting procedures. The results aim to inform whether tegileridine can provide effective and well-tolerated analgesia for patients with moderate-to-severe postoperative pain following abdominal procedures.

Inclusion Criteria:

• Adults 18-65 years; BMI 18-35 kg/m²; ASA physical status I-III.

  • Diagnosed with symptomatic gallbladder stone disease and scheduled for elective laparoscopic cholecystectomy under general anesthesia; expected procedure duration ≥60 minutes and postoperative hospitalization ≥24 hours.

    • Investigator expects moderate-to-severe postoperative pain; willing to receive standardized multimodal analgesia and protocolized rescue analgesia.

      • Able to understand pain scales (NRS/VAS) and provide written informed consent.

        • Women of childbearing potential: negative pregnancy test within 72 hours preoperatively and agreement to use effective contraception through 30 days after last dose.

Exclusion Criteria:

• Known hypersensitivity to opioids or any component of the study drug.

  • Chronic opioid use/tolerance (e.g., ≥30 mg MME/day for ≥7 consecutive days within 30 days pre-op) or current methadone/buprenorphine therapy.

    • Planned/required neuraxial analgesia (epidural/spinal), continuous peripheral nerve blocks, or use of long-acting local anesthetic formulations that would confound postoperative pain assessment; brief intraoperative wound infiltration with short-acting local anesthetics is allowed if standardized.

      • Significant respiratory disease (e.g., uncontrolled obstructive sleep apnea, GOLD III-IV COPD) or anticipated postoperative mechanical ventilation >24 hours.

        ⑤Severe hepatic or renal impairment (Child-Pugh B/C; eGFR <30 mL/min/1.73 m²; or ALT/AST >3×ULN with total bilirubin >2×ULN).

        ⑥Clinically unstable cardiovascular or cerebrovascular disease (e.g., shock, uncontrolled arrhythmias, myocardial infarction or stroke within 6 months), or persistent SBP <90 mmHg.

        ⑦Concomitant medications that cannot be safely withheld: MAO inhibitors within 14 days; strong CNS depressants requiring continued use (e.g., benzodiazepines/barbiturates); mixed agonist-antagonist opioids (e.g., nalbuphine, buprenorphine) within 7 days.

        ⑧Severe psychiatric/neurologic disease or communication/cognitive impairment precluding valid pain scoring or follow-up.

        ⑨Pregnancy or breastfeeding; unwillingnebass to use contraception.

        ⑩Substance abuse (alcohol or drugs) within 12 months.

        ⑪Participation in another interventional study with study drug/device within 30 days.

        ⑫Any other condition that, in the opinion of the investigator, makes participation unsafe or impractical (e.g., severe active infection, planned ICU admission).