A Study to Evaluate the Efficacy and Safety of CG5503 Prolonged Release (PR) in Subjects With Moderate to Severe Chronic Pain Due to Osteoarthritis of the Knee

Inclusion Criteria:

• Patients diagnosed with osteoarthritis of the knee based on the American College ofRheumatology (ACR) criteria and functional capacity class of I- III;

• Patients taking analgesic medications for at least 3 months prior to screening anddissatisfied with their current therapy;

• Patients requiring opioid treatment must be taking daily doses of opioid- basedanalgesic, equivalent to <160 mg of oral morphine;

• Baseline score of >=5 on an 11-point numeric rating scale, calculated as the averagepain intensity during the last 3 days prior to randomization.

Exclusion Criteria:

• History of alcohol and/or drug abuse in Investigator's judgment;

• Chronic hepatitis B or C, or HIV, presence of active hepatitis B or C within the past 3 months;

• Life-long history of seizure disorder or epilepsy;

• History of malignancy within past 2 years, with exception of basal cell carcinoma thathas been successfully treated;

• Uncontrolled hypertension;

• Patients with severely impaired renal function;

• Patients with moderate to severely impaired hepatic function or with laboratory valuesreflecting inadequate hepatic function,

• Treatment with neuroleptics, monoamine oxidase inhibitors, serotonin norepinephrinereuptake inhibitors (SNRI), tricyclic antidepressants, anticonvulsants, oranti-parkinsonian drugs, treatment with any other analgesic therapy thaninvestigational medication or rescue medication during the trial.