The objective of this study is to evaluate the efficacy and safety of TDS-943 (topical diclofenac spray) compared to oral celecoxib and placebo in subjects with osteoarthritis of the knee. The main hypotheses are that TDS-943 will be better than placebo and no worse than celecoxib.

This is a multicenter, outpatient, multiple-dose, placebo- and active controlled, double-blind, double-dummy parallel group, randomized (stratified by unilateral vs. bilateral knee OA) trial. The trial will enroll subjects who have been diagnosed with OA of the knee (confirmed by weight-bearing x-ray) and whose condition is in flare at baseline. Subjects who qualify to enter the study will be randomized to topical TDS-943 40 mg bid, oral celecoxib 200 mg qd, or placebo in a 3:2:2 ratio.

Inclusion Criteria:

• Males or females in generally good health at least 40 years of age
• Osteoarthritis (OA) of at least one knee, verified by a weight-bearing radiograph
• Subject has taken an oral NSAID or analgesic at least 3 days during the past 30 days to treat knee OA pain

Exclusion Criteria:

• Females who are pregnant or lactating or who may become pregnant
• Hypersensitivity (exacerbations of asthma, rhinitis, or urticaria) to sulfonamides, acetaminophen, diclofenac, celecoxib, aspirin, or any other NSAID
• History of myocardial infarction, congestive heart failure, stroke, coronary-artery bypass graft surgery, or any other significant cardiovascular disease, or is on any form of anticoagulation therapy other than low-dose aspirin (no more than 325 mg/day)