A Study of the Efficacy and Safety of 2PX in Patients With Pain Due to Osteoarthritis of the Knee

Inclusion Criteria: * Male and female out-patients, 40 years or older. * Subjects with documented OA of either one or both knees, as defined by the American College of Rheumatology (ACR) criteria (\[Altman R, Asch E, Bloch D, et al (1986)\]); i.e.knee pain and at least 3 out of the following 6 criteria in the target joint: * age \>50 years * stiffness \< 30 minutes * crepitus * bony tenderness * bony enlargement * no palpable warmth * Radiological evidence of joint space narrowing in the target joint within 8 weeks prior to randomisation. * Subjects with chronic, moderate to severe OA pain of the target knee: * present for more than 3 months, and for ≥ 20 days per month. * not controlled by, or intolerant of, oral NSAIDs, paracetamol, COX-2 inhibitors or weak opioids. * intensity at least moderate (i.e., actual WOMAC (pain questions 1-5) ≥ 10) on WOMAC OA index LK 3.1 at Visit 1, in the target knee, as recalled over the last 24 hours. Exclusion Criteria: * Subjects with any moderate to severe pain of other origin (e.g., fibromyalgia) which could confound assessment or self-evaluation of pain due to OA in the target knee. * Subjects with any prosthesis fitted to the target knee. * Subjects requiring treatment with any of the following agents/therapies within the specified periods or at any time during the study are excluded from participation: * Any potent/strong opioid in the 4 weeks prior to randomisation (i.e., an opioid assumed to cause withdrawal symptoms upon abrupt discontinuation). * Any topical or subcutaneously applied analgesic agents (e.g., capsaicin, NSAIDs) applied to the target knee within 7 days prior to randomisation. * Any treatment which could alter the degree or nature of baseline OA pain planned within the study period. * Intra-articular injections of corticosteroids in the target knee within the 2 months prior to randomisation. * Intra-articular injections of hyaluronan in the target knee within 6 months prior to randomisation. * Avascular necrosis in the target knee within 6 months prior to randomisation. * Arthrosynthesis of the target knee within 12 months prior to randomisation. * Arthroscopy of the target knee within 6 months prior to randomisation. * Major trauma to the target knee within 6 months prior to randomisation. * Infection in the target knee within 6 months prior to randomisation. * Subjects who have previously been treated with 2PX. * Subjects who have received an investigational drug or used an investigational device within the 30 days prior to randomisation. * Subjects with a significant psychiatric disorder, in the opinion of the investigator, or subjects receiving strong anti-psychotic medication. * Subjects with documented or suspected alcohol or drug abuse. * Any ongoing or past history of malignant disease within the 5 years immediately prior to randomisation (with the exception of basal cell carcinoma). * Pregnancy or ongoing lactation * Female subjects of childbearing potential unwilling to use adequate contraceptive measures throughout the duration of the study. For the purpose of this study, adequate contraception is defined as: * oral, injected or implanted hormonal methods of contraception; OR * placement of an intrauterine device (IUD) or intrauterine system (IUS); OR * barrier methods of contraception: Condom or occlusive cap (diaphragm or cervical/vault caps) with spermicidal foam/gel/film/cream/suppository Note: Male sterilisation or abstinence are not acceptable methods of birth control and would preclude enrolment in the study. Note: For post-menopausal women: less than 12 months since the last spontaneous menstrual bleeding will exclude the patient unless they are willing to utilise acceptable methods of contraception for the duration of the study. * Male subjects able to conceive, who are unwilling to use barrier methods of contraception throughout the duration of the study * Subjects unable to comply with the study assessments.