Efficacy and safety of extended-release, once-daily tramadol in chronic pain: a randomized 12-week clinical trial in osteoarthritis of the knee.

The efficacy and safety of a once-daily extended-release formulation of tramadol hydrochloride (tramadol ER) was evaluated in patients with moderate to severe chronic pain of osteoarthritis (OA). This was a randomized, double-blind, placebo-controlled, parallel-group, 12-week study. Eligible patients with radiographically confirmed OA of the knee meeting the American College of Rheumatology diagnostic criteria, defined by knee pain and presence of osteophytes, plus at least age >50 years, morning stiffness <30 minutes in duration, and/or crepitus, entered a 2-7 day washout period during which all analgesics were discontinued.