The goal of this clinical trial is to learn if fixed-dose combination etoricoxib 90 mg + diacerein 50 mg capsule works to treat knee/hip osteoarthritis-associated pain in adults. It will also learn about the safety of the drug. The main questions it aims to answer are:

Does etoricoxib+diacerein reduce pain intensity as per WOMAC scale after 60 days? What medical problems do participants have when taking etoricoxib 90 mg+diacerein 50 mg capsule for 60 days? Researchers will compare the test drug etoricoxib 90 mg+diacerein 50 mg capsule to an active comparator (meloxicam 15 mg + diacereina 50 mg) to see if drug ABC works to treat pain in patients with osteoarthritis.

Participants will:

Take drug the test or comparator drugs every day for 60 days. Visit the clinic once a month for health and outcomes follow-up. Keep a diary of their symptoms, pain intensity, WOMAC scale, adverse events, rescue medication use, other used drugs, and treatment adherence.

Inclusion Criteria:

1. Adult men and women (≥ 18 and ≤ 65 years of age).

2. Patients who agree to participate in the study by signing the informed consent form.

3. Patients with a clinical diagnosis of knee or hip OA according to the American College of Rheumatology criteria with radiographic evidence of OA (K-L score ≥2) in the index joint (defined as the joint with OA being evaluated in this study).

   1. A joint previously treated by joint replacement surgery cannot be considered an index joint.
   2. A joint surgically intervened within the previous year cannot be considered an index joint.
   3. If a patient has a K-L score of ≥2 in more than one joint (knees or hip), the index joint will be the joint with the highest WOMAC pain subscore.
   4. If two or more of the patient's joints (knees or hip) have a K-L score of ≥2 and the same WOMAC pain subscore, the index joint will be the joint with the highest K-L score.
   5. If two or more joints (knees or hip) have a K-L score of ≥2, the same WOMAC pain subscore, and the same K-L score, the investigator may choose one of these joints as the index joint based on medical judgment.

4. Patients with moderate to severe pain in the index joint defined as a WOMAC pain subscore of ≥4.

5. Patients who, in the investigator's medical judgment, can discontinue current analgesic medications and are willing to comply with the study requirements.

Exclusion Criteria:

1. Patients with allergy or hypersensitivity to the study medications (including the rescue medication) or to any of their excipients.
2. Patients with a body mass index ≥ 39.
3. Patients with a history of rapidly progressive hip OA.
4. Patients with a history of inflammatory joint disease other than OA (e.g., rheumatoid arthritis, lupus erythematosus, psoriatic arthritis, pseudogout, acute gout, joint infections) or seronegative spondyloarthropathy, Paget's disease of the spine, pelvis, or femur, neuropathic disorders, multiple sclerosis, fibromyalgia, spinal cord tumors or infections, or renal osteodystrophy.
5. History of arthropathy (osteonecrosis, insufficiency fracture of subchondral bone, rapidly progressive osteoarthritis type 1 or type 2), neuropathic joint arthropathy, hip dislocation, knee dislocation, extensive subchondral cysts, significant bone collapse, significant loss of bone mass, or pathological fractures.
6. Scheduled joint replacement surgery to be performed during the study period, or arthroscopic procedures within 6 months prior to study initiation.
7. Trauma to the index joint within 30 days prior to the screening visit.
8. Use of systemic corticosteroids within 30 days prior to the screening visit or intra-articular corticosteroids in the index joint within 12 weeks prior to the screening visit.
9. Concomitant use of medications with laxative effects.
10. Continuous oral treatment (at least 90 days) with a SYSADOA medication (chondroitin sulfate, glucosamine sulfate, diacerein, or other) within 3 months before the start of the study.
11. Use of monoamine reuptake inhibitors, tricyclic antidepressants, selective serotonin reuptake inhibitors, and serotonin-norepinephrine reuptake inhibitors for pain treatment within 4 weeks prior to the screening visit.
12. History of peptic ulcer or gastrointestinal bleeding within 12 months prior to the screening visit and/or medical contraindication for the use of NSAIDs.
13. Severe gastrointestinal disorders, including persistent diarrhea (≥3 bowel movements/24 hours).
14. Renal insufficiency (serum creatinine ≥1.8 mg/dL or 2+ proteinuria on a test or a glomerular filtration rate <30 mL/min).
15. Liver enzyme levels (ALT, AST, GST) elevated ≥2.5 times the upper limit of normal at the time of screening.
16. History or presence of cardiovascular diseases (e.g., second- or third-degree heart block, first-degree heart block with abnormal QRS or bifascicular block, history of uncontrolled arterial hypertension, congestive heart failure classified as NYHA stage II-IV, transient ischemic attack (TIA) or stroke within 12 months prior to the screening visit, or myocardial infarction or acute coronary syndromes or evidence of peripheral vascular insufficiency with claudication within 6 months prior to the screening visit).
17. History of other comorbidities that, in the investigator's judgment, could affect the subject's participation in the study, their safety, or the outcome of the study variables.
18. Current history of alcoholism and/or drug abuse.
19. Current participation in a clinical research study evaluating another investigational drug or having received another investigational product within 30 days prior to the screening visit.
20. Women with a positive pregnancy test at the time of screening or who are breastfeeding.