Busulfan has a narrow therapeutic range, and in children, pharmacokinetic variability has been found to be high even after the use of intravenous (i.v.) busulfan. Recently, a reduced toxicity myeloablative regimen showed promising results, but the data of busulfan pharmacokinetics in hematopoietic stem cell transplantation (HSCT) using a targeted busulfan/fludarabine regimen in children has not yet been reported. We performed therapeutic drug monitoring (TDM) after once-daily i.v. busulfan combined with fludarabine and analyzed the outcomes. Busulfan (i.v.) was administered once daily for 4 consecutive days. The daily target area under the curve (AUC) was 18,125-20,000 μg*h/L/day (4415-4872 μmol*min/L/day), which was reduced to 18,000-19,000 μg*h/L/day (4384-4628 μmol*min/L/day) after a high incidence of toxicity was observed. A total of 24 patients were enrolled. After infusion of busulfan on the first day, patients showed AUC that ranged from 12,079 to 31,660 μg*h/L (2942 to 7712 μmol*min/L) (median 16,824 μg*h/L, percent coefficient of variation (%CV) = 26.5%), with clearance of 1.74-6.94 mL/min/kg (median 4.03 mL/min/kg). We performed daily TDM in 20 patients, and during the daily TDM, the actual AUC ranged from 73% to 146% of the target AUC, showing high intraindividual variability. The %CV of busulfan clearance of each individual ranged from 7.7% to 38.7%. The total dose of busulfan administered for 4 days ranged from 287.3 mg/m(2) to 689.3 mg/m(2). Graft failure occurred in 3 patients with total AUC less than 74,000 μg*h/L (18,026 μmol*min/L), and 2 patients with relatively high total AUC experienced veno-occlusive disease. Busulfan pharmacokinetics showed high inter- and intraindividual variability in HSCT using a targeted busulfan/fludarabine regimen, which indicates the need for intensive monitoring and dose adjustment to improve the outcome of HSCT. Currently, we are performing a newly designed phase II study to decrease regimen-related toxicities and reduce graft failure by setting an optimal target AUC based on this study.

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Conditioning regimens for pediatric acute lymphoblastic leukemia (ALL) usually include total body irradiation (TBI), but TBI may result in serious sequelae. Busulfan and cyclophosphamide have been used as an alternative to TBI. Etoposide also has been widely used to enhance antileukemic effect. However, toxicities have been reported in some studies using busulfan, cyclophosphamide, and etoposide regimen. A reduced toxicity myeloablative regimen using busulfan and fludarabine showed promising results. Also, therapeutic drug monitoring (TDM) and administration of targeted doses of busulfan have been recommended to improve the outcome of hematopoietic stem cell transplantation (HSCT). In this study, we evaluated the outcome of HSCT using a targeted once-daily i.v. busulfan-fludarabine-etoposide (BuFluVP) regimen in pediatric and infant ALL. Busulfan (age ≥ 1 year, 120 mg/m(2); age < 1 year, 80 mg/m(2)) was administered once daily as the first dose on day -8, and a targeted dose of busulfan was used according to the TDM results on days -7 to -5. Forty-four patients were evaluated. Donor-type neutrophil engraftment was achieved in all patients. Veno-occlusive disease occurred in 7 patients (15.9%), but all patients were successfully treated. Cumulative incidence of treatment-related mortality and relapse were 9.1% and 9.9%, respectively. One-year overall survival and event-free survival rates of all patients were 86.2% and 83.8%, respectively. Twelve patients (27.3%) were infants at diagnosis, and their 1-year overall survival rate was 83.3%. Our study demonstrated that HSCT using a targeted once-daily i.v. BuFluVP regimen showed favorable outcomes and could be an option for HSCT in pediatric and infant ALL.

3019FN2 Introduction: Itraconazole is a widely used antifungal agent with a broad spectrum of activity, but pharmacokinetics has large inter- and intra-individual variability. The optimal usages of itraconazole from numerous pharmacokinetic studies have been proposed in adults. However, application of itraconazole in pediatric patients is limited since its pharmacokinetics in children is less known. This study assessed the efficacy of the empirical use of intravenous (IV) itraconazole in pediatric patients undergoing hematopoietic stem cell transplantation and investigated the pharmacokinetics of repeated-doses of itraconazole and its active metabolite hydroxyitraconazole. Patients & Methods: Efficacy was evaluated in 85 patients undergoing hematopoietic stem cell transplantation (32 allogeneic, 53 autologous). Oral itraconazole prophylaxis (2.5 mg/kg twice daily) was started on the day -2 of the conditioning chemotherapy. Itraconazole was changed to IV form in patients with persistent neutropenic fever over 2 days (5 mg/kg twice daily for 2 days for induction and 5 mg/kg daily for maintenance). Itraconazole was continued until the absolute neutrophil count was over 1, 000/uL, the development of fungal disease, the development of unacceptable drug toxicity or death, or the withdrawal from study. Empirical treatment was considered successful if all of the following criteria were met: successful treatment of baseline fungal infection, absence of breakthrough fungal infection, survival for 7 days after therapy, resolution of neutropenic fever, and no premature discontinuation due to toxicity or lack of efficacy. Full pharmacokinetic study was conducted in 6 patients (1 allogeneic, 5 autologous). For pharmacokinetic study, trough level during oral itraconazole was measured with blood collected before the 5th dose. Blood for trough level of IV administrations were sampled prior to every induction doses and 1–5th IV maintenance doses. For area under the plasma concentration-time curve (AUC) analysis, serial blood samples were collected prior to the 3rd IV maintenance infusion, and 1, 2, 4, 8, 12, 24hr after the infusion. Plasma concentrations of itraconazole and hydroxyitraconazole were determined using a validated HPLC method. Results: The overall success rates fulfilling all criteria were 32.9%. There was no patient with baseline fungal infection, but 1 patient with breakthrough fungal infection, and all patients were survived for 7 days after discontinuation of itraconazole. The rates of resolution of fever in 48 hours after itraconazole were 32.9%, and premature discontinuation occurred in 23.5% of patients. The causes of discontinuation were persistent fever in 17 (20%) patients, and nausea or vomiting in 3 (3.5%) patients. There was no Grade 3–4 toxicity associated with itraconazole. The mean trough plasma concentration of itraconazole after oral prophylaxis and intravenous induction were 577.2 and 1413.3 ng/ml. The median pharmacokinetic values for steady-state itraconazole and hydroxyitraconazole, respectively, were as follows: AUC form 0 to 24 h (AUC24), 42.8 and 63.1 μg · h/ml; clearance (CL) at steady state, 63.5 and 38.5 ml/min; and volume of distribution at steady state (Vdss), 201.8 and 711.2 L. According to the results, sufficient trough level was achieved during oral prophylaxis, and levels were rising rapidly by successive IV inductions so that the steady concentration of twice the level of oral itraconazole was maintained during IV maintenance with this empirical strategy. Compared with a previous pediatric single intravenous study, lower CL for itraconazole and metabolite were observed, which can be explained by saturable drug metabolism with multiple dosing, as found in adults. Dose adjusted steady state AUC24 of itraconazole and metabolite were about twice of those in the adults, and relatively smaller clearance of study drug needs to be considered for pediatric use. Conclusion: IV itraconazole was effective and safe as an empirical antifungal agent in pediatric patients undergoing hematopoietic stem cell transplantation, and this is considered to be due to the fast and satisfactory increase in the drug concentration by switching oral prophylaxis to IV itraconazole. There are considerable pharmacokinetic differences between children and adults with respect to itraconazole and its active metabolite, which should be considered with pediatric usages. Disclosures: No relevant conflicts of interest to declare.

3492 Introduction: Busulfan has narrow therapeutic range. High exposure is associated with systemic toxicity such as veno-occlusive disease (VOD) while underexposure results in graft failure or relapse. In children, pharmacokinetic variability was found to be high even after the introduction of intravenous busulfan. Busulfan is metabolized via liver through conjugation with glutathione S-transferase (GST) family, and inter-individual variability may be explained by GST polymorphisms. Thus, we investigated the influence of GST polymorphisms on the clinical outcomes of hematopoietic stem cell transplantation (HSCT) with busulfan based conditioning regimen in children. Patients and methods: We studied patients who underwent HSCT at Seoul National University Children's Hospital from November, 2001 to November, 2008. IV busulfan (0.8 mg/kg/dose for patients≥10 kg and 1.1 mg/kg/dose for patients <10 kg, q 6hr for 4 days) was used in combination with cyclophosphamide or fludarabine as conditioning regimen. Etoposide was added for acute lymphocytic leukemia (ALL). GST polymorphisms (GSTA1 375 A > G, -52 G > A, -567 G > T, -631 G > T, -69 C > T, GSTM1 deletion, GSTT1 deletion, and GSTP1 313 A > G) were analyzed by multiplex PCR amplification and SNP genotyping. Results: A total of 70 patients (48 male, 22 female) were analyzed. The diagnoses were ALL in 32, AML in 26, and other diseases in 12 patients. Median age at HSCT was 8.8 years (range 1.0–19.0 years). Bone marrow or peripheral blood stem cell transplantations (BMT/PBSCT) were conducted in 42 patients, and cord blood transplantations (CBT) in 28 patients. Graft failure occurred in 11 (15.7%) patients (1 (2.4%) in BMT/PBSCT, 10 (35.7%) in CBT) and relapse occurred in 15 (21.4%) patients (12 (28.6%) in BMT/PBSCT, 3 (10.7%) in CBT) after HSCT. Patients having GSTA1 *A/*A and GSTP1 313 A/A genotype (N=33) showed higher incidence of graft failure than the others (N=37) (27.3% vs 5.4%, P =.01). Conversely, the incidence of hyperbilirubinemia over grade 3 was significantly lower in the patients with GSTA1 *A/*A and GSTP1 313 A/A genotype than the other patients (6.1% vs 24.3%, P =.05). Event free survival (EFS) of patients with GSTA1 *A/*A and GSTP1 313 A/A genotype was significantly lower than the EFS of the other patients in both BMT/PBSCT and CBT, and the main causes of event were graft failure in CBT and relapse in BMT/PBSCT. Conclusions: In children undergoing HSCT with busulfan based conditioning regimen, GST A1 and P1 polymorphisms seem to have influence on the graft failure, relapse and complications. To confirm our results, further studies about the influence of GST A1 and P1 polymorphisms on the pharmacokinetics of busulfan are needed. Disclosures: No relevant conflicts of interest to declare.