Study on the Safety and Effectiveness of Switching Between Two Forms of Tapentadol in Patients With Chronic Low Back Pain

Inclusion Criteria: * Diagnosis of Low Back Pain (LBP) of non-malignant origin present for at least 3 months immediately before study entry * Taking drug treatment for pain for at least 3 months before screening and who are dissatisfied with current therapy * Subjects receiving opioid treatment must have a total daily opioid dose \<= 160 mg/day of oral morphine equivalent * For entry into open label period patients must have a baseline score \>=5 on an 11-point NRS, calculated as the average pain intensity during the last 3 days of the washout period * For entry into the double-blind period subjects must have remained on the same optimal stable dose and frequency of tapentadol (CG5503) IR administration during the last 3 days of the open-label treatment period Exclusion Criteria: * Presence of conditions other than Low Back Pain (LBP) that could make it hard to assess or self-evaluate pain * Surgery in low back area within 3 months of screening or expected surgery in the low back area during the study * Any scheduled surgery or painful procedure during the study, or any clinically significant disease that, in the opinion of the investigator, may affect efficacy or safety assessments * History of malignancy within the past 2 years, with the exception of basal cell carcinoma that has been treated and is no longer present * Women who are pregnant or breast-feeding * Moderately or severely impaired liver function * Severely impaired kidney function * History of chronic hepatitis B or C, or HIV, or presence of active hepatitis B or C in past 3 months * History of seizure disorder * Alcohol or drug abuse * Uncontrolled high blood pressure * Clinically relevant history of hypersensitivity, allergy, or contraindications to acetaminophen or opioid analgesics (or ingredients)