Ilona Steigerwald,1 Matthias Müller,1 Jolanta Kujawa,2 Jean-Charles Balblanc,3 Jaime Calvo-Alén,41Medical Affairs Europe & Australia, Grünenthal GmbH, Aachen, Germany; 2Medical University of Lodz, Medical Rehabilitation Clinic, Lodz, Poland; 3Department of Rheumatology, General Hospital of Belfort, Belfort, France; 4Hospital Universitario Sierrallana and IFIMAV Research Institute, Universidad de Cantabria, Cantabria, SpainAbstract: This open-label, phase 3b study (ClinicalTrials.gov Identifier: NCT00983073) evaluated the effectiveness, and tolerability of tapentadol for severe, chronic osteoarthritis knee pain that was inadequately managed with World Health Organization (WHO) Step I or II analgesics or co-analgesics, or that was not treated with regular analgesics. Prior to starting study treatment, patients discontinued any WHO Step II analgesics, while Step I analgesics and/or co-analgesics were continued at the same dose. Patients received tapentadol prolonged release (50–250 mg bid) during a 5-week titration period and a 7-week maintenance period. Doses of tapentadol immediate release 50 mg (≤twice/day; ≥4 hours apart) were permitted throughout the study (total daily dose of tapentadol prolonged and immediate release, ≤250 mg bid). The primary endpoint was the change in pain intensity on an 11-point numerical rating scale-3 (NRS-3; recalled average pain intensity [11-point NRS] during the last 3 days) from baseline to Week 6, using the last observation carried forward (LOCF) to impute missing pain intensity scores. The mean (standard deviation) change from baseline to Week 6 (LOCF) in pain intensity was -3.4 (2.10; P < 0.0001) for all patients evaluated for effectiveness (n = 195). Significant decreases in pain intensity were also observed at Weeks 6, 8, and 12 (all P < 0.0001) using observed-case analysis. Corresponding significant improvements from baseline to Weeks 6 and 12 were observed in the Western Ontario and McMaster Universities osteoarthritis index, the EuroQol-5 Dimension health status questionnaire, the Short Form-36 health survey, and the Hospital Anxiety and Depression Scale (all P ≤ 0.0103). Treatment-emergent adverse events were in line with those observed in previous studies of tapentadol prolonged release. Overall, the results of this study indicate that tapentadol treatment results in significant improvements in pain intensity, health-related quality of life, and function in patients with inadequately managed, severe, chronic osteoarthritis knee pain.Keywords: tapentadol, osteoarthritis, chronic pain, opioid