Extended-release tramadol in the treatment of osteoarthritis: a multicenter, randomized, double-blind, placebo-controlled clinical trial.

OBJECTIVE: This study evaluated the efficacy and safety of tramadol extended-release (tramadol ER) tablets once daily in subjects with osteoarthritis pain. METHODS: This 12-week, multicenter, randomized, double-blind, placebo-controlled, parallel-group clinical trial included 1020 adults with osteoarthritis of the knee or hip and baseline pain intensity >or= 40 on a 100-mm pain visual analog scale (0 = no pain, 100 = extreme pain). Subjects took placebo or were titrated to a target dose of tramadol ER 100, 200, 300, or 400 mg once daily. MAIN OUTCOME MEASURES: The co-primary efficacy variables were pain and physical function subscales of the WOMAC Osteoarthritis Index and subject global assessment of disease activity. RESULTS: Mean changes in WOMAC Osteoarthritis Index pain and physical function subscales were significantly different between tramadol ER and placebo, overall (p