CG5503 is a centrally active pain-relieving drug being investigated for the treatment of acute and chronic pain. This study was designed to assess the safety and tolerability of CG5503 IR in patients who need joint replacement of the hip or knee due to chronic osteoarthritis. This is a double-blind study, i.e., neither patients nor investigators will know what treatment is given. Before the start of the 10 day double-blind phase, each patient will be screened for eligibility and eligible patients will be randomly assigned to receive either CG5503 IR, oxycodone IR, or placebo (i.e., no active drug). All patients will take their treatment by mouth every 4 to 6 hours during waking hours. A total of 60 doses (up to 6 doses per day) of study treatment will be provided for each patient during the 10-day treatment phase. The study treatment will be dispensed on Day 1, and patients will take the first dose in the evening of the same day. The effectiveness of study treatment (CG5503 IR, oxycodone, or placebo) will be assessed using several measures, including 11 Point Pain Numerical Rating Scale, 5-Point Relief Numerical Rating Scale, and Patient Global Impression of Change. Using these scales, patients will indicate their pain intensity level, pain relief level, and overall status of their well-being. Safety and tolerability will be assessed using physical examination, monitoring of adverse events, clinical and laboratory measures, and 12 lead ECG results. The null hypothesis for the study is that all CG5503 IR dosage efficacy results are equal to placebo based on the 5-day SPID in the treatment of chronic pain caused by osteoarthritis. The alternative study hypothesis is that at least 1 CG5503 IR dose effect will be different from placebo effect. CG5503 IR 50 mg, 75 mg of the base, 10 mg oxycodone or placebo for 10 days taken by mouth every 4 to 6 hours during waking hours. Patients randomized to CG5503 IR 75 mg group will receive CG5503 IR 50 mg on Day 1 and 75 mg on Day 2 to 10. All doses of study treatment should be taken with approximately 120 mL of water with or with food.