Could methadone ease agonizing mouth pain in kids after transplant?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * All subjects admitted will receive a myeloablative conditioning regimen followed by autologous or allogeneic bone marrow transplant during transplant admission. Conditioning may include chemotherapy, radiation, or a combination of both methods to be determined by primary attending transplant physician. Diagnoses will include but not limited to those with liquid tumors, solid tumors, hematological/congenital blood disorders, or severe combined immunodeficiency syndromes. * Subjects must be 6-18 years of age and demonstrate understanding of PCA use or have a parent available for PCA by proxy, meaning parent can push the button for the patient. Patient maximum age is 18 years old. PCA proxy in compliance with Pain Assessment and Management policy per institution. * Performance status: Karnofsky/Lansky \>50% prior to receiving conditioning. * Be cognitively able to utilize and understand patient-controlled analgesia (PCA). * Informed consent will be obtained from all participants or their parents or guardians, assent will be obtained from children ages 10-17 years of age per institutional policy. Exclusion Criteria: * QT prolongation prior to receiving myeloablative conditioning as evidenced by QTc being \>450 for both girls and boys prior to starting methadone. * Medical history of QT prolongation, VF, or VT. * Patients on chronic pain medications on admission or have received more than 30 days of continuous opioids over the past month. * Patients receiving a non-myeloablative regimen or no conditioning. * Neurological or psychiatric condition that could confound reliable assessment of pain and sedation (non-verbal, global delay). * History of allergic reactions attributed to compounds of similar chemical or biologic composition to morphine or other agents used in study. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that, in the opinion of the investigator, would limit compliance with study requirements. * History of opioid misuse disorder OR opioid risk assessment tool score \>8.