26DT052; Scaling Busulfan Dose to Body Surface Area in Children

Busulfan is a drug used in conditioning regimens for bone marrow transplantation. Busulfan levels outside the desired range can cause excessive side effects or failure of bone marrow engraftment. The initial dose of busulfan is currently scaled to body weight; on subsequent days the dose may be adjusted to achieve busulfan levels in a therapeutic range. However, only half of children receiving a busulfan dose scaled to body weight achieve therapeutic blood levels after the first dose. We performed computer simulations of alternative dosing methods for infants and children, and identified that dosing based on body surface area (BSA) could significantly increase the number of children achieving therapeutic blood levels after the first dose. This study will test whether this new dosing method results in a higher percentage of patients achieving the desired busulfan blood levels after the first dose. The study will enroll up to 38 children receiving high doses of busulfan as part of their standard conditioning regimen prior to bone marrow transplant. We will use the busulfan blood levels that are routinely measured after the first dose to determine the effectiveness of our new dosing method.

Inclusion criteria

• Subject age: ≤21 years
• Body Surface Area (BSA):

• Group A: BSA ≥0.5 m2
• Group B: BSA <0.5 m2
• Planned for once-daily busulfan-containing conditioning regimen pre-bone marrow transplant
• Scheduled to have TDM after the first dose of busulfan
• Diagnosis: both benign and malignant conditions are eligible

Exclusion criteria

• At the time of enrollment, patients may not receive medications that significantly alter busulfan clearance, as specified below.

a. If patients had received the drugs listed below prior to enrollment, the following washout periods, based on ≥ 6 times drug t½, are required.

Deferasirox: ≥7 days Metronidazole: ≥7 days Ketoconazole, voriconazole: ≥7 days Itraconazole, posaconazole: ≥14 days Phenytoin: ≥21 days