This randomized, single-blind, parallel-group study will investigate the efficacy and the tolerability of a combination treatment of etoricoxib (30 mg/day) plus controlled-release oxycodone (10 mg/day) compared with a titrated dose of etoricoxib up to 60mg/day as monotherapy , in patients with Chronic Low Back Pain (CLBP) who have not responded to the starting dose of Etoricoxib 30mg/day. A common clinical question is that is it better to increase the dose of the current monotherapy or to combine both treatments early on, in patients who do not respond to standard start doses of NSAIDs like etoricoxib.