The purpose of this study is to identify the dose(s) of IDEA-033 that will provide a meaningful effect for treating osteoarthritis of the knee.

The objective of this double-blind, placebo-controlled, randomized study is to evaluate the safety of and to identify the dose(s) of IDEA-033 that will provide a minimum clinically meaningful effect for treating the signs and symptoms of osteoarthritis of the knee. This study will also compare the safety profile of the three doses of IDEA-033 in treating the signs and symptoms associated with osteoarthritis for 12 weeks. The primary hypothesis is that at least one of the three doses of IDEA-033 is superior to placebo with respect to three primary efficacy endpoints of WOMAC Pain, WOMAC Physical Function, and Subject Global Assessment of Response to Therapy. A second hypothesis is that there is an increase in efficacy with increasing doses of IDEA-033.

Patients will receive one of five treatments for 12 weeks:Three doses of IDEA-033, or naproxen 1 g over-encapsulated tablet + placebo or placebo

Inclusion Criteria:

• Osteoarthritis of both knees for minimum of six months
• Moderate pain in the most involved knee when not taking NSAIDs
• Must have used an oral NSAID on at least three days per week for last three months or 25 of 30 days before screening
• Demonstrate x-ray evidence of osteoarthritis in the most involved knee during the last six months

Exclusion Criteria:

• Grade 1 or Grade 4 severity of the most involved knee based on x-ray criteria
• Intra-articular injections or arthroscopy of the most involved knee during three months before Screening visit
• Inflammation of the most involved knee that could be related to gout or pseudogout-induced synovitis or infection
• A large bulging effusion
• History of gout or pseudo-gout induced synovitis or infection of the more severe knee
• History of partial or total knee replacement in either knee