A Study to Look at Tapentadol Tablets in Children and Adolescents in Pain

Inclusion Criteria: Part 1 - Randomized to open-label, active comparator controlled treatment Participants were eligible for the study at enrollment if all the following applied: * Informed consent (if applicable assent) obtained. * Male or female participant at least 6 years of age at the Enrollment Visit and less than 18 years of age on Day 14. * Participant has an underlying long-term pain condition (e.g., cancer, chronic disease, planned or performed surgery) that is, according to the judgment of the investigator, expected to require a twice-daily prolonged release opioid treatment until at least the end of the 14-day Treatment Period. * Participant can swallow tablets of appropriate size. * Participant is able to participate in the study as planned and willing to comply with the requirements of the protocol including refraining from drinking beverages containing alcohol and recreational intake of drugs while on study medication. Participants had to satisfy the following criteria before allocation to treatment: * Less than 18 years of age. * No opioid intake or last calculated morphine equivalent dose of less than 3.5 mg/kg per day. * Participant has a body weight of at least 17.5 kg. * If a female of childbearing potential (post menarchal and not surgically incapable of childbearing) and sexually active, must practice an effective method of birth control (e.g., prescription oral contraceptives, contraceptive injections, intrauterine device, double barrier method, contraceptive patch) before allocation to study medication until the end of intake of study medication. * If a female and post menarchal or older than 12 years, has a negative urine pregnancy test on the day before or on the day of allocation to study medication. Part 2 Inclusion criteria for the Tapentadol Open-label extension period: * Participant has completed the 14-day Treatment Period. * Participant is still in need of prolonged release opioid treatment. * Participant does not meet any of the compulsory discontinuation criteria. Exclusion Criteria: Participants were not eligible for the study if any of the following applied. The following was checked at enrollment: * Has been previously enrolled in this study or a previous study with tapentadol. * Has a clinically relevant history of hypersensitivity, allergy, or contraindication to morphine or tapentadol or any ingredient, including galactose intolerance (see investigator's brochure for tapentadol prolonged-release \[PR\] and summary o…