A Study to Characterize the Pharmacokinetics and Tolerability of Buprenorphine Patches in Children With Moderate to Severe Mouth Pain

Inclusion criteria: 1. Male or female children experiencing severe mouth pain secondary to chemotherapy induced mucositis requiring opioid analgesic therapy and who will be an inpatient, as a minimum up to Day 8 (patch removal). 2. Subjects experiencing 'severe' pain in the Investigators clinical judgment. 3. Body weight ≥ 15 kg. Subjects weighing ≥ 25 kg will be recruited in the first phase of the study with those weighing \< 25 kg also being included in the second phase, (after a successful review by an IDSMC). Upper age range to be 16 years. 4. In dwelling IV cannula or central line from which blood can be obtained. 5. Written informed consent obtained from parent(s)/legal representative, and where possible assent obtained from the subject if appropriate, in line with local regulations. 6. Females of child bearing potential must have a negative urine pregnancy test if the Principal Investigator considers there to be a reasonable possibility of pregnancy. Exclusion criteria: 1. Subjects with known hypersensitivity to buprenorphine or any of its excipients in the transdermal system, as outlined in the Summary of Product Characteristics for BuTrans. 2. Known hypersensitivity to other opioids. 3. Skin disease affecting application or local tolerance of BTDS. 4. Clinically significant history of allergic reaction to wound dressings or adhesives. 5. Severe respiratory impairment. 6. Clinically significant hepatic dysfunction. 7. Severe renal impairment. 8. Subjects who are receiving MAO inhibitors or have taken them within the previous 2 weeks. 9. Subjects receiving hypnotics or other central nervous system (CNS) depressants that, in the investigator's opinion, may pose a risk of additional CNS depression with study medication. 10. Subjects who have taken any buprenorphine preparations in the last 14 days. 11. Subjects with myasthenia gravis. 12. Subjects with convulsive disorders, head injury, shock, or reduced level of consciousness of uncertain origin. 13. Subjects who are currently participating in another clinical research study involving a new chemical entity (NCE) unless the sole purpose of the other trial at the time of BUP1501 screening is for long term follow-up/survival data or subjects who have participated in a clinical study within the previous 30 days. Participation in a chemotherapy clinical trial that is not evaluating a NCE will be accepted for inclusion. 14. Subjects who are pregnant, lactating or in the Investigators opinion are at risk of conceiving. 15. Previous enrollment in this clinical study. 16. Subjects who the Investigator believes are unsuitable for the study.