The purpose of this study is to evaluate the efficacy and safety of extended release (ER) tramadol hydrochloride (HCl)/acetaminophen compared with placebo in participants with chronic (lasting a long time) low-back pain.

This is a double blind (a medical research study in which neither the researchers nor the participants know what treatment the participants is receiving), randomized (study drug is assigned by chance), placebo-controlled, parallel group (a medical research study comparing the response in 2 or more groups of participants receiving different interventions [treatments]) and up-titration study in participants with chronic low back pain. The study will consist of 6 visits (Day -7 to Day -1 [Visit 1], Day 1 [Visit 2], Day 3 [telephone visit], Day 8 [Visit 3], Day 15 [Visit 4] and Day 29 [Visit 5]) and 2 phases: a screening phase and treatment phase. Screening phase will be of 7 days during which, participants will receive stable dose of non-steroidal anti-inflammatory drugs (NSAIDS) or COX-2 selective inhibitors (NSAID that specifically inhibits an enzyme known as cyclooxygenase-2) for pain therapy. On the basis of average pain intensity over the last 48 hours which will be measured at baseline (at the end of screening period), participants will enter the treatment phase. Treatment phase will be of 28 days which includes 7-days of dose titration period. In treatment phase all participants will be randomly assigned to 1 of 2 possible treatments: tramadol HCl 75 milligram (mg)/acetaminophen 650 mg ER tablet treatment or the equivalent placebo (an inactive substance) treatment until study completion, Day 29. Participants will receive 1 tablet of tramadol HCl/acetaminophen ER or its equivalent placebo, once daily for 3 days. After the first 3 days, the participants will receive a telephone inquiry monitoring the occurrence of adverse events and will be given additional administration instructions for the next 4 days (1 tablet twice daily for 4 days). From Day 7, participants will receive 1 or 2 tablets twice a day depending on the degree of pain relief required. Participants will visit the center on the Day 8 (Visit 3), Day 15 (Visit 4), and Day 29 (Visit 5) after starting study drug. The efficacy will be assessed by measuring extent of reduction in pain intensity on a Visual Analog Scale (VAS). Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Participants diagnosed with low back pain at least 3 months before the screening or washout period
• Participants who have taken a stable dose of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) (drugs used for reducing inflammation and pain ) or Cyclo-Oxygenase 2 (COX-2) selective inhibitors (an anti-inflammatory drug that fights pain) from 7 days before investigational product administration, and could maintain the same dose during the period of the study
• Participants whose average pain intensity is more than or equal to 4.0 centimeters on Visual Analog Scale over the last 48 hours after the completion of screening
• Postmenopausal or surgically sterile or abstinent women or practicing a highly effective method of birth control
• Women with childbearing potential must have negative pregnancy test

Exclusion Criteria:

• Participants who have taken tramadol or tramadol HCl or acetaminophen, or narcotic (strong habit-forming drug that stops pain and depresses the central nervous system) analgesic tablet within 30 days before investigational product administration
• Participants who have taken acetaminophen tablet within 7 days before investigational product administration
• Participants with tumor or infection in meninges or spinal cord
• Participants who have fibromyalgia (neurosensory disorder characterized by muscle pain, joint stiffness, and fatigue), reflex sympathetic dystrophy (feeling of pain associated with evidence of minor nerve injury) or causalgia (persistent, severe burning sensation of the skin), acute spinal cord compression, acute nerve root compression, severe lower extremity weakness or numbness, regional pain syndrome, meningitis (inflammation of the meninges), diskitis (nonbacterial inflammation of an intervertebral disk or disk space), back pain because of secondary infection or tumor, or pain caused by a confirmed or suspected neoplasm
• Participants who have taken analgesic (including local agents or anesthetics), sedative-hypnotic (e.g., diazepam), or muscle relaxant other than a stable dose of NSAIDs or COX-2 selective inhibitors within 5 times the half-life of the concerned agent before investigational product administration