Study of Clofarabine and Fludarabine Drug Exposure in Pediatric Bone Marrow Transplantation (HCT)

Fludarabine and clofarabine are nucleoside analogs with potent antitumor and immunosuppressive properties used in conditioning regimens of pediatric allogeneic hematopoietic cell transplantation (alloHCT) to promote stem cell engraftment. This is a single-center, prospective, non-interventional pharmacokinetic (PK) study investigating the clinical pharmacology of combination nucleoside analogue therapy in 24 children undergoing alloHCT at University of California, San Francisco Benioff Children's Hospital. Patients would receive clofarabine and fludarabine regardless of whether or not they decide to consent to PK sampling. Clofarabine and fludarabine doses will not be adjusted based on PK data. The investigators will apply the combination of a limited sampling strategy and population PK methodologies to determine specific factors influencing clofarabine and fludarabine exposure in pediatric alloHCT recipients and identify exposure-response relationships. Subjects will undergo PK sampling of clofarabine and fludarabine drug concentrations over the duration of combination therapy (3 to 5 days). To evaluate sources of variability impacting clofarabine and fludarabine exposure clinical data will be obtained from the patient's medical chart on each day of PK sampling. To assess exposure-response relationships neutrophil engraftment, treatment-related toxicity, and survival data will be collected through day 100 post-transplant.