An Efficacy and Safety Study of Extended Release (ER) Tramadol Hydrochloride (HCl)/Acetaminophen in Participants With Chronic Low-Back Pain

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