Pharmacokinetics of fludarabine and its association with clinical outcomes in paediatric haematopoietic stem cell transplantation patients

Fludarabine is used as a common component of conditioning regimens for haematopoietic stem cell transplantation (HSCT). However, knowledge regarding the pharmacokinetic characteristics of once-daily fludarabine dosing in children is limited. This study investigated the pharmacokinetics of fludarabine and evaluated its associations with clinical outcomes in paediatric patients. A total of 802 blood samples obtained from 43 paediatric patients who underwent HSCT were included in a population pharmacokinetic analysis using non-linear mixed-effects modelling. The relationships between systemic 9-β-d-arabinofuranosyl-2-fluoroadenine (F-ara-A) exposure derived from the model and the clinical outcome variables were explored. A two-compartment model with proportional residual error adequately described the pharmacokinetics of F-ara-A. The body surface area and glomerular filtration rate were significant covariates for the clearance of F-ara-A. After the first dose of fludarabine at 40 mg/m ² , the median (min—max) values for the area under the concentration-time curve (AUC) from dosing to infinity and the elimination half-life were 4696 (3056–10,477) ng·h/mL and 7.95 (4.78–10.88) h, respectively. No significant associations were found between systemic exposure and graft-vs.-host disease, neurologic and pulmonary complications, relapse or survival. Systemic exposure was comparable to that of previous reports from different populations and had no association with clinical outcomes.