A Multi-Center, Randomized, Double-Blind, Placebo/Active-Controlled Phase II Clinical Study to Evaluate the Efficacy and Safety of HSK21542 Injection for Postoperative Pain Treatment in Orthopedic Surgery

18 years old ≤ age ≤74 years old, regardless of gender;

18 kg/m2≤BMI≤32 kg/m2, meet the weight range specified in the protocol;

American Society of Anesthesiologists (ASA) grade 1-3;

Accept hip replacement 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;

Patients with allergy to opioids or any component of the trial drug;

Patients with a history of severe cardiovascular and cerebrovascular diseases, ,and psychiatric disorders;

Last use of opioid or non-opioid analgesics less than 5 half-lives or the duration of drug efficacy prior to randomization; use of drugs with unclear half-lives that may affect analgesic efficacy within 7 days prior to randomization, or last use of drugs affecting analgesic efficacy less than 5 half-lives prior to randomization, as well as Chinese herbal medicines or proprietary Chinese medicines deemed by the investigator as potentially impacting the evaluation of efficacy and safety;

Continuous use of opioid analgesics for more than 7 days for any reason within 30 days prior to screening;

Laboratory test results during the screening period meeting any of the following criteria: 1) Significantly abnormal hematology results; 2) Significantly abnormal prothrombin time test results; 3) Significantly abnormal liver or kidney function; 4) Significantly abnormal fasting blood glucose;

Positive test results during the screening period for hepatitis B surface antigen (HBsAg), hepatitis C antibody (HCVAb), syphilis antibody, or human immunodeficiency virus (HIV) antibody;

A history of drug, drug, and/or alcohol abuse

Participate in any clinical trail within 30 days;

Pregnant or lactating female subjects;

Subjects of childbearing potential who are unwilling to use contraception throughout the study period or plan to become pregnant within 3 months after the study.

Subjects with any other factor considered by the investigator to be ineligible for participation in the trial.