NCT01728246.

Methods	Official title: a randomized controlled trial on the efficacy, safety and quality of life effects of add‐on tramadol/acetaminophen combination in chronic osteoarthritis Open‐label, randomized controlled study to evaluate the efficacy, safety and effects on quality of life of tramadol/acetaminophen as an add‐on therapy in Filipino participants with chronic pain because of chronic OA. Participants will be randomly assigned to 2 groups: tramadol/acetaminophen group and non‐tramadol/acetaminophen group. Participants in tramadol/acetaminophen group will receive celecoxib 200 mg and fixed‐dose combination of tramadol 37.5 mg/acetaminophen 325 mg as add‐on therapy, and participants in non‐tramadol/acetaminophen group will receive celecoxib 200 mg only. Total duration of study will be 4 weeks. Participants in both groups will be given celecoxib 200 mg once daily for 4 weeks. In addition, participants in the tramadol/acetaminophen group will be given add‐on tramadol/acetaminophen doses 3 times/day for 4 weeks. Participants will be asked to return for follow‐up at weeks 2 and 4. Efficacy will be assessed using 100‐mm VAS while quality of life will be assessed using the Oswestry Disability Index. Participant safety will be monitored throughout the study.
Participants	Diagnosed with chronic OA of knee or hip for ≥ 1 year, and aged ≥ 18 years.
Interventions	Celecoxib 200 mg once daily and tramadol 37.5 mg and acetaminophen 325 mg, for 4 weeks Celecoxib once daily and non‐tramadol and acetaminophen, for 4 weeks
Outcomes	Major outcomes: Change from baseline in VAS for Pain score at week 2 Change from baseline in VAS for Pain score at week 4 Change from baseline in Oswestry Disability Index score at week 2 Change from baseline in Oswestry Disability Index score at week 4 Percentage of participants who discontinued because of rescue medication Time to discontinuation because of rescue medication
Notes	Study start date: October 2007 Primary completion date: May 2008 Study completion date: May 2008 Contact information: Address: Paranaque City, Metro Manila, Philippines, 1700 Email: info@janbe.jnj.com Phone: +32 14 60 21 11 ClinicalTrials.gov identifier: NCT01728246

ACR: American College of Rheumatology; BPI: Brief Pain Inventory; BS‐11: Box Score‐11; IR: immediate release; LBP: low back pain; ME: morphine‐equivalent; NRS: numerical rating scale; NSAID: non‐steroidal anti‐inflammatory drug; OA: osteoarthritis; PI: pain intensity; PI‐NRS: pain intensity numerical rating scale; PID: pain intensity difference; VA: Veteran Affairs; VAS24: visual analog scale for the last 24 hours; WOMAC: Western Ontario and McMaster Universities Arthritis Index.