• The proportion of patients with "sustained pain control" for the 5-day fixed-dose phase phase determined by numeric rating scale and the number of rescue dose prescribed at fixed dose period.
  

• 24-hour numeric rating scale; visual analogue scale; rescue dose; proportion of patient achieved dose adjustment; sleep questionnaire; patient's global impression of change; adverse event; vital signs; ECG examinations;serum tapentadol concentration,etc
  

Tapentadol is an analgesic as effective as conventional mu-opioid analgesics and the safety profiles are expected to be more favorable for the gastrointestinal system as represented by nausea/vomiting and constipation. This is a multicenter, open-label, uncontrolled, optional dose-titration study. tapentadol PR will be administered orally twice daily (every 12 hours) before meal. For patients previously using opioids, the initial dose of tapentadol PR will be selected depending on the daily dose of opioid at the completion of screening period. For opioid-naive patients, the initial dose of tapentadol PR will be 25 mg b.i.d. Patients receive the same dose tapentadol PR for the first 2 days of the dose-adjustment phase and from Day 3, the dose can be titrated under the investigator's or subinvestigator's discretion up to the maximum of Day 14. Patients are then applied fixed dose regimen for 5 days as same as that used at the end of the dose-adjustment phase. This study consists of 3 to 7 days of screening period, 3 to 14 days of dose adjustment period, 5 days of fixed dose period and 7 days of follow-up period. The efficacy endpoints are 24-hour Numeric Rating Scale score, 100-mm visual analogue scale, achievement of dose adjustment, rescue dose, status of treatment discontinuation due to any adverse event or lack of efficacy, sleep questionnaire and Patient's global impression of change. The safety endpoints are adverse events, vital signs, laboratory examinations and electrocardiogram examination. Pharmacokinetic endpoints is to measure the serum tapentadol and tapentadol-O-glucuronide concentrations.

Tapentadol PR will be administered orally twice daily. The initial dose will be determined by previously used opioid or 25 mg b.i.d (opioid-naive patients). Patients receive the same dose for the first 2 days of the dose-adjustment phase and from Day 3, the dose can be titrated under the investigator's or sub-investigator's discretion up to the maximum of Day 14. Patients are then applied fixed dose regimen for 5 days the same as that used at the end of the dose-adjustment phase.