Efficacy and Safety Study of Gabapentin as add-on to Morphine in Paediatric Patients Affected by Chronic Pain

Inclusion Criteria: 1. Male or female, aged 3 months to less than 18 years at screening (V1) 2. Informed consent by parent(s) and/or legal guardian according to each country legal requirement. 3. Assent, where applicable, according to each country legal requirement.Informed (co-) consent of child, where applicable, according to each country legal requirement. 4. Subjects that meet the diagnostic criteria for neuropathic or mixed pain. 5. Subjects that present with chronic pain defined as the recurrent or continuous pain persisting more than 3 months. 6. Subject that present with severe pain as defined by average pain intensity of ≥7 /10 as assessed during a 3-day screening period 7. Stable underlying disease condition and treatment. 8. Patients with Chemotherapy Induced Peripheral Neuropathy, when in clinical remission or maintenance phase of their therapeutic protocol. Exclusion Criteria: 1. Pain duration of more than 5 years. 2. Current use of gabapentin. 3. Current use of strong opioids (morphine, methadone, fentanyl, ketamine, oxycodone). 4. History of failure to respond to adequate treatment by gabapentin or opioids for neuropathic pain. 5. History of epileptic condition (except febrile seizure disorder). 6. Subjects with diagnosis of sickle cell disease. 7. Subjects that present significant cognitive impairment. 8. Subjects that present current, controlled or uncontrolled, co-morbid psychiatric diagnosis that can impair pain diagnosis and assessment such as severe depressive conditions or psychosis. 9. Subjects with history of or current suicidal ideation or behaviour. 10. Subjects with history of substance abuse in particular opioids. 11. Subjects under prohibited concomitant medication . 12. Subjects with a body mass index (BMI) for age and gender of \< 5th percentile or \> 95th percentile (charts provided as Appendix 3). 13. Subjects with significant renal impairment, i.e., glomerular filtration rate \< 90 mL/min/1.73 m2 (Revised Schwarz equation). 14. Subjects with significant hepatic impairment or with Aspartate Transaminase (AST) or Alanine Transaminase (ALT) enzymes 3 times the upper limit of the age-specific reference range. 15. Subjects in need for corticosteroid oral treatment or corticosteroid infiltrations to treat pain caused by infiltration or compression of neural structures, e.g. peripheral nerves or spinal cord. 16. Subjects with clinically relevant abnormal ECG at the screening visit in the discretion of the Investigator/cardiologis…