A Clinical Trial Evaluating the Efficacy and Safety of HSK55718 in Patients for Postoperative Pain Treatment in Abdominal Surgery

Inclusion Criteria: * Age ≥18 years old, regardless of gender; * 18 kg/m2≤BMI≤30 kg/m2; * American Society of Anesthesiologists (ASA) gradeⅰ-ⅲ; * Accept abdominal surgery under general anesthesia; * Within 4 hours after the end of surgery, NRS≥4 in the resting state at any time; * Fully understand and voluntarily participate this trial, and sign the informed consent form; Exclusion Criteria: * A history of cardiovascular, respiratory, neurological, or psychiatric diseases that meet the protocol-defined exclusion criteria. * Clinically significant abnormalities in laboratory tests during the screening period. * A history of severe drug allergy or known allergy to the investigational drug. * Continuous use of opioid analgesics for more than 10 days for any reason within 3 months prior to randomization. * Use of any medication that may affect analgesia, where the last dose was administered less than 5 half-lives of that drug before randomization. * A history of drug abuse, substance abuse, and/or alcohol abuse within the past year. * Pregnant or lactating women. * Participation in another drug clinical trial within 3 months prior to the screening period. * Presence of any sensory dysfunction. * Presence of any painful physical condition. * Subjects with any other factor considered by the investigator to be ineligible for participation in the trial.