• The primary outcome is the change from baseline at randomization in average pain intensity over the last week of the double-blind maintenance period at Week 12, as determined by twice-daily measurements on an 11-point numerical rating scale. [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]
  

• The proportion of patients achieving various levels of pain improvement based on the percent change from pre-titration at Week 12 of the double-blind maintenance period on an 11-point numerical rating scale. [ Time Frame: 15 weeks ] [ Designated as safety issue: No ]
  

The primary objective of this randomized-withdrawal (randomized means study medication assigned to patients by chance and withdrawl means to stop using), multicenter, double-blind (neither patient nor investigator knows the study medication), placebo-controlled, Phase 3 study is to determine the effectiveness and safety of orally administrated Tapentadol (CG5503) extended release (ER) (base) at doses of 100-250 mg twice daily in patients with moderate to severe pain from diabetic peripheral neuropathy. The study is being conducted for registration and approval of CG5503 in the US and outside US. The trial will consist of two phases: Phase I is open-label and Phase 2 is double- blind. In the Open-Label Phase 1 there will be four periods: screening (to assess eligibility) , washout (dependent on the pain medication the patient was previously taking), pain intensityperctoris evaluation (over a 3 day period), and open-label titration (study drug will be titrated to an optimal dose starting with 50 mg twice a day and adjusted to an optimal dose for a period of 3 weeks). Patients with at least a 1-point reduction in the average pain intensity score at the end of the open-label titration period, as compared with pre-titration will be eligible for randomization in the double-blind phase. In the double-blind Phase 2, there will be two periods: double-blind maintenance period (take drug for 12 weeks), and follow-up (a visit within 4 days of the intake of the last dose of study drug and a follow-up call approximately 10-14 days after the intake of the last dose of the study drug). The patient will maintain the dose level achieved at the end of the Phase 1 during the double-blind treatment phase. The study hypothesis is that the study drug will be different from placebo in the change in pain intensity.

Titrate Tapentadol (CG5503) extended release (ER) 50 mg to patient's optimal dose ranging between 100mg and 250mg twice a day; Placebo (no active ingredients). All doses of trial treatment will be taken orally with or without food, for a maximum timeframe of 15 weeks.