• The primary outcomes include incidence of adverse events, changes in laboratory measures, results of physical exams, and results of 12-Lead ECG.over one year.
  

• The secondary outcomes, among others, include COWS and SOWS assessments; patient assessment of constipation symptoms; vomiting and sleep assessments; pain intensity assessment; patient global impression of change over one year.
  

CG5503 is a centrally active pain-relieving drug being investigated for the treatment of acute and chronic pain. This study is a randomized (patients are assigned different treatments based on chance), open-label (both the Investigator and the patient know what medication is allocated), active-controlled, parallel-group, multicenter study. It is designed to investigate the long-term safety (side effects during up to one year of administration) and effectiveness (level of pain control) of CG5503 PR compared to oxycodone (an opioid commonly used for relief of moderate to severe pain). The doses of both of these medications will be adjusted to give the best therapeutic benefit for the patient. Approximately 1075 patients will be screened. Safety evaluations include monitoring of adverse events, physical examinations, and clinical laboratory tests. Assessments of pain relief include the pain intensity numeric rating scale, and patient global impression of change scale (PGIC). Venous blood samples will be collected for the determination of serum concentrations of CG5503 and oxycodone.     

Patients will start taking CG5503 PR 50 mg BID or oxycodone CR 10 mg. After 3 days (6 consecutive doses), the dose will be increased: CG5503 to 100 mg BID, oxycodone to 20 mg. The patient will remain on this dose for the next 4 days.During maintinance phase, upward titration may occur at a minimum of 3 day-intervals in increments of CG5503 PR 50 mg BID or oxycodone 10 mg BID. The maximum doses are CG5503 PR 250 mg BID or oxycodone 50 mg BID.

Inclusion Criteria:

• Clinical diagnosis of knee or hip osteoarthritis with history of pain at the reference joint for at least 3 months or clinical diagnosis of low back pain of benign origin for at least 3 months
• Must be dissatisfied with their current analgesic therapy (e.g. Non-steroidal anti-inflammatory drugs NSAIDS, COX-2 inhibitors, opioids, paracetamol/acetaminophen
• Have a pain intensity >4 on Numerical Rating Scale

Exclusion Criteria:

• Life-long history of seizure disorder or epilepsy
• Any of the following within one year: mild/moderate traumatic brain injury, stroke, transient ischemic attack, and brain neoplasm
• Severe traumatic brain injury within 15 years (consisting of more than one of the following: brain contusion (injuries resulting in hemorrhage), intracranial hematoma, unconsciousness or post traumatic amnesia lasting for more than 24 hours) or residual sequelae suggesting transient changes in consciousness
• History of malignancy within past 2 years, with exception of a successfully treated basal cell carcinoma
• Presence of significant pain associated with conditions other than osteoarthritis or low back pain that could confound the assessment or self-evaluation of pain