• SPID sum of pain intensity differences over 48 hours [ Time Frame: 48 hours ] [ Designated as safety issue: No ]
  

• Secondary effectivenes outcomes include, among others, the effect of CG5503 IR on the time needed for the first rescue pain medication during the double-blind treatment period, the SPID at 6, 12, 24, and 72 hours relative to first dose. [ Time Frame: 72 hours ] [ Designated as safety issue: No ]
  

Subjects undergoing bunionectomy often experience moderate to severe acute pain post-surgery. Normally such pain is controlled when subjects receive repeated doses of opioid analgesics. However, opoid therapy is commonly associated with side effects such as nausea, vomiting, sedation, constipation, addiction, tolerance, and respiratory depression. CG5503, a newly synthesized drug with an immediate release (IR) formulation, also acts as a centrally acting pain reliever but has a dual mode of action. The aim of this trial is to investigate the effectiveness (level of pain control) and safety (side effects) of CG5503 IR 75mg compared with no drug (placebo) or one dose of morphine (an opoid commonly used to treat post-surgical pain). This trial is a randomized, double-blind (neither investigator nor patient will know which treatment was received), active- and placebo-controlled, parallel-group, multicenter trial to evaluate the treatment of acute pain after bunionectomy. The trial will include a blinded 72 hour inpatient phase immediately following bunionectomy, during which subjects will be treated with either 75-mg CG5503 IR, a placebo, or 20-mg morphine, and pain relief will be periodically assessed. Assessments of pain relief include the pain intensity numeric rating scale (PI), pain relief numeric rating scale (PAR), and patient global impression of change scale (PGIC). Safety evaluations include monitoring of adverse events, physical examinations, and clinical laboratory tests. Venous blood samples will be collected for the determination of serum concentrations of CG5503 and morphine. The alternative trial hypothesis is that at least 1 dose strength of CG5503 will be different from placebo in controlling pain at 48 hours.