The purpose of this study is to analysis of the pharmacokinetics of fludarabine for hematopoietic stem cell transplantation in pediatric patients.

Fludarabine is a commonly used chemotherapeutic agent for hematopoietic stem cell transplantation in children. However, no pharmacokinetic study has thus far been conducted in pediatric patients. Fludarabine can cause adverse reactions which include neurotoxicity, damage to lungs. Pharmacokinetic study is critical to predict the safety of fludarabine in pediatric patients.

Through an individualized pharmacokinetic study (which entails numerous samplings) of fludarabine in pediatric patients, this study aims to develop a sampling-minimized analysis method and study the population pharmacokinetics.

Through a pharmacokinetic analysis, we aim to evaluate whether pediatric patients show similar population pharmacokinetics of adults, for whom fludarabine is authorized, and evaluate the safety (toxicity) and efficacy (event free survival).

Inclusion Criteria:

1. Conditioning regimen including fludarabine

2. Age: < 19 years old

3. Functional class: ECOG 0-2

4. No loss of function of major organs. Criteria may be individualized.

   • Heart: shortening fraction > 30%, ejection fraction > 45%.
   • Liver: total bilirubin < 2 ⅹ upper limit of normal; ALT < 3 ⅹ upper limit of normal.
   • Kidney: creatinine < 2 ⅹ normal or a creatinine clearance (GFR) > 60 ml/min/1.73m2.

5. No active viral or fungal infection

6. Appropriate hematopoietic stem cell donor

7. Informed consent from patients' parents

Exclusion Criteria:

1. Pregnant or breast feeding
2. Disease progression due to clinical test
3. Psychiatric disease may interfere with clinical test
4. Whether attending physician consider the patient inappropriate for study enrollment