Double Blind Efficacy and Safety Study of Flexible-Dose vs Low-Dose Q8003 After Undergoing Primary Unilateral Total Knee Arthroplasty

Inclusion Criteria: * At least 18 years of age at time of enrollment. * If female, be at least one year post-menopausal, surgically sterile or practicing effective contraceptive, be non-lactating, and if of child-bearing potential, have a negative urine pregnancy test result. * Have a body mass index (BMI) of 38 kg/m2 or less. * Have undergone a primary unilateral total knee arthroplasty performed under under standardized general, spinal or epidural anesthesia. * Have developed moderate to severe pain (a score of 2 or more on the 4 point Likert scale and at least 4 on the 11 point NPRS scale within 6 hours of discontinuing PCA on the morning after surgery). Exclusion Criteria: * In the opinion of the Investigator, has a history of pulmonary, cardiovascular (including uncontrolled hypertension), neurologic, endocrine, hepatic, gastrointestinal, or kidney disease or therapy that, in the opinion of the Investigator, would jeopardize the patient's well being by participation in this study or is mentally or emotionally unsuitable to participate, or unable/unwilling to comply with the study assessments. * Used opiates continuously (including tramadol) for more than ten days in the past year. * Hypersensitivity or poor tolerance to ibuprofen or short term opioids. * Currently receiving any medications that are not at a stable dose (the same dose for \> 2 months prior to date of surgery). * Was dosed with another investigational drug within 30 days prior to the Screening Visit or has previously received treatment with Q8003. * Current therapy with central nervous system depressant medications that might increase the risks of treatment with opioids (other than those used with surgical anesthesia). * Current evidence of alcohol abuse (regularly drinks more than 4 units of alcohol per day; 1 unit = ½ pint of beer, 1 glass of wine, or 1 ounce of spirit). * History of abusing licit or illicit drug substances within five (5) years of study entry. * Has taken drugs known to interact with morphine or oxycodone metabolism, including, but not limited to, phenothiazines, monoamine oxidase inhibitors (MAOI), amphetamines, and muscle relaxants within the 4 weeks prior to the date of surgery. * History of sleep apnea.