The purpose of this study is to evaluate the efficacy and safety of meloxicam nanocrystal injection in subjects with moderate to severe pain after abdominal surgery.

In this study, a randomized, double-blind, placebo-controlled multicenter study will be conducted to evaluate the efficacy and safety of meloxicam nanocrystal injection in subjects with moderate to severe pain after abdominal surgery.

Inclusion Criteria:

1. 18 years ≤ age ≤ 65 years, regardless of gender.
2. Elective abdominal surgery under general anesthesia.
3. ASA score of grade 1-3.
4. 18 kg/m^2 < BMI < 30 kg/m^2.
5. NRS score of ≥ 4 within 3 hours after the end of surgery (last suture).
6. Able to understand the study process and the use of pain scales, and able to communicate effectively with study personnel.
7. Written informed consent signed by subject or legal representative.

Exclusion Criteria:

1. Abnormal liver function: ALT and/or AST > 2 × ULN, or TBIL ≥ 2 × ULN.
2. Renal impairment (blood creatinine > 1.5 × ULN), or dialysis treatment within 28 days prior to the surgery.
3. Subjects at high risk of bleeding, including subjects with congenital bleeding disorders (e.g., hemophilia), thrombocytopenic subjects (platelet count less than 50 × 10^9/L), subjects with abnormal platelet function (e.g., idiopathic thrombocytopenic purpura, disseminated intravascular coagulation, congenital abnormal platelet function), or subjects with any clinically significant active bleeding.
4. Abnormal coagulation (PT>ULN+3s and/or APTT>ULN+10s).
5. Subjects with a history of severe gastrointestinal disease (e.g. ulcers, bleeding and perforation, etc.) within 1 year prior to randomization that may be worsened by the administration of NSAIDs-like drugs.
6. Myocardial infarction or coronary artery bypass grafting within 1 year prior to randomization.
7. Abnormal clinically significant 12-lead ECG during the screening period and judged by the investigator to be inappropriate for participation in this trial.
8. Combination of severe liver, kidney, cardiovascular, cerebrovascular, or metabolic system disease, which is judged by the investigator to be inappropriate for participation in this trial.
9. Subjects with combined neurological or psychiatric disorders such as migraine and seizures, which have been judged by the investigator to affect the evaluation of the efficacy of the trial drug.
10. Subjects with hypertension whose blood pressure is not satisfactorily controlled by antihypertensive medication (screening period sitting systolic blood pressure ≥ 160 mmHg, and/or screening period diastolic blood pressure ≥ 100 mmHg).
11. Sitting systolic blood pressure ≤ 90 mmHg at screening.
12. Subjects with diabetes mellitus whose blood glucose is not satisfactorily controlled (random blood glucose ≥ 11.1 mmol/L during the screening period).
13. Subjects with advanced malignancy or malignancy with extensive metastases.
14. Combined with other physical pain conditions that may confound postoperative pain evaluation.
15. Subjects with known hypersensitivity to meloxicam, any of the excipients in the study drug, aspirin, other non-steroidal anti-inflammatory drugs (NSAIDs), any perioperative drug use, or other history of anaphylactic reactions.
16. Subjects with alcohol or drug dependence within 3 months prior to screening and/or subjects whose alcohol, drug, or medication withdrawal may interfere with efficacy and safety evaluations during the study period.
17. Subjects who have undergone abdominal surgery within 6 months prior to randomization.
18. Subjects who have participated in other clinical trials and received the test drug/test device within 3 months prior to randomization.
19. Subjects with contraindications to investigational drugs, standard anesthetic practices.
20. Women who are pregnant or breastfeeding.
21. Other reasons that the investigator deems inappropriate for participation in the trial.