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 of product characteristics for morphine PR), or naloxone. * History or current condition of any one of the following: * Seizure disorder or epilepsy. * Serotonin syndrome. * Traumatic or hypoxic brain injury, brain contusion, stroke, transient ischemic attack, intracranial hematoma, posttraumatic amnesia, brain neoplasm, or episode(s) of more than 24 hours duration of unconsciousness. * History or current condition of any one of the following: * Moderate to severe renal or hepatic impairment. * Abnormal pulmonary function or clinically relevant respiratory disease (e.g., acute or severe bronchial asthma, hypercapnia) * Complex regional pain syndrome. * A pain indication with a strong psycho-somatic component that, in the judgment of the investigator, is unlikely to respond to opioids. * History of alcohol or drug abuse in the investigator's judgment, based on history and physical examination. Drugs of abuse detected in urine screen unless explained by allowed concomitant medication * Participant has: * A clinically relevant abnormal electrocardiogram. * Signs of pre-excitation syndrome. * Brugada's syndrome. * QT or corrected QT (QTcF, Fridericia) interval greater than 470 ms. * Any surgery scheduled during the first 14 days of the study that is expected to require post-surgical intensive care unit (ICU) treatment, or that requires post-surgical parenteral pain-treatment, or may, affect the safety of the participant. * Participant is not able to understand and comply with the protocol as appropriate for the age of the participant or participant is cognitively impaired in the investigator's judgment such that they cannot comply with the protocol. * Participant, parent or the legal representative is an employee of the investigator or study site, with direct involvement in the proposed study or other studies under the direction of that investigator or study site, or family member of the employees or the investigator. The following was checked at the enrollment and the allocation visits: * Has a concomitant disease or disorder (e.g., endocrine, metabolic, neurological, psychiatric, infection) that in the opinion of the investigator may affect or compromise participant safety during the study participation. * Pancreatic/biliary tract disease (e.g., pancreatitis) or paralytic ileus. * Intake of forbidden concomitant medication/use of forbidden therapies (see synopsis section Concomitant medications/therapies). * Female participant is breastfeeding a child. The following was checked at the allocation to treatment visit: * Has received a drug or used a medical device not approved for human use within 30 days prior to visit. * Based on data from the local laboratory, one or more of: * Total serum bilirubin greater than 2.0 mg/dL. * Serum albumin less than 2.8 g/dL. * Aspartate transaminase or alanine transaminase greater than 5 times upper limit of normal. * Based on data from the local laboratory, creatinine clearance less than 30 mL/min per 1.73 m2 (calculated according to a formula that is appropriate for the respective age group).