The main objective is to assess the efficacy of a new formulation containing chondroitin sulfate and glucosamine sulfate (CS+GS) compared with placebo in patients with primary osteoarthritis of the knee.

The purpose of this study is to determine whether a new combination of chondroitin sulfate and glucosamine sulfate administered once a day is superior to placebo in the treatment of patients with moderate to severe knee osteoarthritis. Eligible patients will be randomized 1:1 and the treatments will be administered for 24 weeks. Clinical efficacy at the end of treatment will be evaluated. Safety will be evaluated through adverse events recoding during the study period.

Inclusion Criteria:

• Patient >= 45 years .
• Primary OA of the knee according to ACR criteria.
• OA radiological grade II-III according to Kellgren and Lawrence.
• Patients with moderate-severe pain.

Exclusion Criteria:

• Patients with clinical significant trauma or surgery in the target knee.
• Concurrent arthritic disease (antecedents and/or current signs) that could confound or interfere with the evaluation of pain efficacy such as chondrocalcinosis, Paget's disease of the ipsilateral limb to the target knee, rheumatoid arthritis, aseptic osteonecrosis, gout, septic arthritis, ochronosis, acromegaly, haemochromatosis, Wilson's disease, osteochondromatosis, seronegative spondyloarthropathy, mixed connective tissue disease, collagen vascular disease, psoriasis, inflammatory bowel disease or fibromyalgia.
• Pain in other parts of the body greater than the knee pain that could interfere with the evaluation.
• Subjects with any active acute or chronic infections requiring antimicrobial therapy, or serious viral (e.g., hepatitis, herpes zoster, HIV positivity) or fungal infections.
• Clinical diagnosis established of uncontrolled diabetes mellitus.
• Patients with asthma.
• History of hypersensitivity to the active drugs or any excipients of the formulations.

6 months