A Safety and Effectiveness Study of Acetaminophen (4000 mg/Day) and Naproxen (750 mg/Day) in the Treatment of Osteoarthritis of the Hip or Knee

Inclusion Criteria: * Osteoarthritis of the hip or knee for a minimum of six months duration requiring treatment with either an analgesic or anti-inflammatory agent on a regular basis (greater than or equal to three days/week) for at least three months * History of osteoarthritis of the hip or knee characterized by pain of mild or moderate intensity * Radiographic evidence of grade 2 or 3 osteoarthritis based on the Kellgren and Lawrence radiographic entry criteria * Physical ability must be either American College of Rheumatology (ACR) Functional Class I or II * Following the washout period, reports mild to moderately severe pain over the previous 24 hours and demonstrates a minimum increase of 20% in the WOMAC Osteoarthritis Index pain subscale score, relative to the screening score. Exclusion Criteria: * History of surgery, including arthroscopy, or major trauma to the study joint in the previous 12 months * Radiographic evidence of severe osteoarthritis of the study joint based on the Kellgren and Lawrence radiographic criteria of grade 4 osteoarthritis * Signs of active study joint inflammation including redness, warmth, and/or, if qualifying with osteoarthritis of the knee, a large, bulging effusion of the study knee joint with the loss of normal contour of the joint at the screening visit or at the baseline examination after the washout period * Morning stiffness of \>30 minutes duration * Significantly incapacitated or disabled and would be categorized as ACR Functional Class III (able to perform only few or none of the duties of usual occupation or self-care) or IV (largely or wholly incapacitated), or unable to walk without assistive devices