Steigerwald I, Müller M, Kujawa J, Balblanc JC, Calvo-Alén J. Effectiveness and safety of tapentadol prolonged release with tapentadol immediate release on-demand for the management of severe, chronic osteoarthritis-related knee pain: results of an open-label, phase 3b study. J Pain Res. 2012;5:121-138. doi:10.2147/JPR.S30540