Buprenorphine for the Management of Pain in Children With Sickle Cell Disease

The goal of this clinical trial is to learn whether a single dose of buccal buprenorphine (BELBUCA) is safe when used in place and/or with full agonist opioids that would otherwise be started during a sickle cell pain crisis admission, in adolescents and young adults (ages 12-22) with sickle cell disease (SCD) who are hospitalized for acute pain. The main questions it aims to answer are: * Is a single dose of buccal buprenorphine, given at doses between 75 and 450 micrograms, safe in this population? * Does buccal buprenorphine reduce the amount of full agonist opioid pain medicine participants need through their patient-controlled analgesia (PCA) pump, and does it change pain scores? * Are participants and their care team satisfied with pain management when buccal buprenorphine is used? * What are the pharmacokinetic properties (how the body absorbs, distributes, and clears the drug) of buccal buprenorphine in this age group? This is a single-arm, open-label, dose-escalation study: every participant receives buccal buprenorphine, and there is no placebo or separate comparison group. Instead, researchers will compare each participant's own opioid use and pain scores in the 8 hours before receiving buccal buprenorphine to the 8 hours afterward, to see whether the dose reduces the need for additional opioid pain medicine. Participants will: * Be treated first with standard-of-care patient-controlled analgesia (PCA) pain medicine (hydromorphone) during the early, acute-stabilization phase of their hospital stay. * Once their pain is stable and they meet criteria to transition to oral opioids, as would happen under usual care, they will receive a single dose of buccal buprenorphine instead, at a dose (75, 150, 300, or 450 micrograms) assigned according to a dose-escalation design. * Continue to have access to demand-only PCA pain medicine for breakthrough pain after the study dose. * Undergo continuous monitoring of heart rate, oxygen level, and carbon dioxide leve