Clinical Research Directory

Inclusion Criteria: * Scheduled for ophthalmic surgery under general anesthesia. * Aged 18 to 70 years. * With American Society of Anesthesiologists (ASA) physical status I to III. * Body mass index (BMI) between 18 and 30 kg/m² * Agree to participate in the trial and provide written informed consent. Exclusion Criteria: * History of cardiovascular or cerebrovascular events within the past 6 months, including unstable angina, ischemic myocardial infarction, or heart failure; or current presence of uncontrolled hypertension (\>180/110 mmHg), aneurysm, or severe cardiac arrhythmia. * Severe respiratory diseases such as pulmonary fibrosis, severe pulmonary abscess, cor pulmonale, or advanced chronic obstructive pulmonary disease (COPD). * Significant neurological disorders such as brain injury or seizures, as well as severe psychiatric illnesses. * Known allergy to kappa opioid receptor agonists or to general anesthetic agents used in this study. * Current peptic ulcer disease, gastrointestinal bleeding, or known hypersensitivity to nonsteroidal anti-inflammatory drugs (NSAIDs), such as flurbiprofen axetil or paracetamol. * Prior use of opioid or non-opioid analgesics, with the last administration occurring within five half-life periods of the drug. * Continuous use of opioid analgesics for more than 10 days within the 3 months prior to screening. * Use of drugs with unknown half-life periods that may affect analgesic efficacy within 14 days before randomization. * History of major surgery within the past 3 months that may interfere with postoperative pain assessment.