Assessment of GRT6005 in Painful Osteoarthritis of the Knee

Inclusion Criteria: * painful Osteoarthritis of the knee based on American College of Rheumatology Criteria * signed informed consent * on stable analgesic medications for painful osteoarthritis with regular analgesic intake for at least 3 months * pain intensity score of 4 or greater on the 11-point numeric rating scale (where 0 indicates "no pain" and 10 indicates "pain as bad as you can imagine"). Exclusion Criteria: * Substance Abuse * Significant cardiac disease * Presence of risk factors for Torsades de Pointes and chronic severe cardiac disease * History of seizure disorder * Chronic gastrointestinal disease * Conditions that contribute and confound to the assessment of pain * Surgery or painful procedure during or within 3 months of enrollment * Cancer * Subjects with impaired renal function * Subjects with impaired hepatic function * Female subjects who are breastfeeding * History of chronic hepatitis B or C or human immunodeficiency virus infection, or presence of acute hepatitis A, B, or C within the past 3 months. * Clinically relevant history of hypersensitivity or allergy to paracetamol, opioids or the excipients.