Therapeutic drug monitoring of intravenous busulfan in Thai children undergoing hematopoietic stem cell transplantation: A pilot study.

Busulfan (Bu) is commonly used in myeloablative conditioning regimens for children undergoing hematopoietic stem cell transplantation. The standard target area under the concentration-time curve (AUC) of Bu is approximately 900-1500 µM min. In previous studies using five fixed doses (0.8-1.2 mg/kg) for Bu without dose adjustment, 75% patients achieved the target AUC. The aim of this pilot study was to determine the percentage of target AUC for intravenous (IV) Bu in Thai children. IV Bu was administered every 6 h over 16 doses. Blood samples were collected for pharmacokinetic (PK) analysis after the first, ninth, and thirteenth doses of Bu. Seven patients (2-14 years; median 6 years) were diagnosed with thalassemia (n = 4), acute myeloid leukemia (n = 2), and pure red cell aplasia. Three, two, and two patients received Bu at 1.1, 1.2, and 0.8 mg/kg, respectively. The AUC of Bu varied from 292-1714 µM min (median = 804). Nine (42.86%), eleven (52.38%), and one (4.76%) AUC values were within, below, and above the target, respectively. The median (range) Bu clearance was 5.93 (1.91-14.65) mL/min/kg. In this study, 42.86% AUC value achieved the target, which was lower than that in previous studies. Therapeutic drug monitoring (TDM) of Bu should be considered in Thai children receiving five fixed doses of IV Bu, and dose adjustment should be performed as necessary. Further PK studies for Bu with a larger sample size are warranted for confirming the necessity of TDM in every step dose of Bu.(Trial registration numbers; TCTR20190528003).

Raman spectroscopy as a potential tool for label free therapeutic drug monitoring in human serum: the case of busulfan and methotrexate.

A methodology is proposed, based on Raman spectroscopy coupled with multivariate analysis, to determine the Limit of Detection (LOD) and Limit of Quantification (LOQ) for therapeutic drug monitoring in human serum, using the examples of Busulfan, a cell cycle non-specific alkylating antineoplastic agent, and, Methotrexate, a chemotherapeutic agent and immune system suppressant. In this study, ultrafiltration is employed to fractionate spiked human pooled serum to efficiently recover the drug in the filtrate prior to performing Raman analysis. The drug concentration ranges were chosen to encompass the recommended therapeutic ranges and toxic levels in patients. Raman spectra were collected from the filtrates in the liquid form, using an inverted backscattering microscopic geometry, using 532 nm as source. Finally, prediction models were built by using Partial Least Squares Regression (PLSR) and LOD and LOQ were calculated directly from the linear prediction models. The LOD calculated for Busulfan is 0.0002 ± 0.0001 mg mL-1, 30-40 times lower than the level of toxicity, enabling the application of this method in target dose adjustment of Busulfan for patients undergoing, for example, bone marrow transplantation. The LOD and LOQ calculated for Methotrexate are 7.8 ± 5 µM and 26 ± 5 µM, respectively, potentially enabling high dose monitoring. The promising results obtained from this study suggest the potential of Raman spectroscopy for therapeutic drug monitoring of drugs in bodily fluids.

Clinical Application of the Dried Blood Spot Method in the Measurement of Blood Busulfan Concentration.

The dried blood spot (DBS) method, which is a simple technique for blood sample processing involving the placement of a drop of whole blood onto filter paper, has been used recently in clinical pharmacology to determine blood concentrations of various drugs. This study examined the feasibility of the clinical application of the DBS method for individual busulfan dose adjustments. Pharmacokinetic (PK) parameters of blood samples for busulfan measurements determined using the DBS method were compared with those using plasma separation (the conventional method). Blood samples were collected from patients receiving i.v. busulfan as a conditioning regimen before allogeneic hematopoietic stem cell transplantation at Toranomon Hospital, Japan. Samples collected 2, 4, and 6 hours after the start of the first drip infusion were processed by DBS or the conventional method. The area under the blood concentration-time curve (AUC) and other PK parameters were calculated to compare the 2 methods. Divergence of <20% in each parameter was considered acceptable. The divergence range for each parameter was as follows: blood concentration at 2 hours after the start of drip infusion, .6 to 8.2%; at 4 hours, .3 to 10.0%; at 6 hours, .3 to 14.2%; and AUC0-∞, .0 to 10.3%. None of the PK parameters showed a divergence between the DBS method and the conventional method exceeding 20%, suggesting that both methods are well correlated. The clinical application of blood sample processing with the DBS method in the measurement of blood busulfan concentration may therefore be feasible, but further studies are needed to confirm these findings.

High-Throughput Validated Method for the Quantitation of Busulfan in Plasma Using Ultrafast SPE-MS/MS.

BACKGROUND: Busulfan is an alkylating agent used to ablate bone marrow cells before hematopoietic stem cell transplantation. Because of its highly variable pharmacokinetics, studies have shown that therapeutic drug monitoring is clinically useful for patients undergoing bone marrow transplant so that toxic effects associated with high drug exposure could be reduced and improve clinical outcomes. Current methods for assaying busulfan include the use of gas chromatography mass spectrometry (GC/MS), high-performance liquid chromatography, and liquid chromatography mass spectrometry. The clinical need for faster turnaround times and increased testing volumes has required laboratories to develop faster methods of analysis for higher throughput of samples. Therefore, we present a method for the quantification of busulfan in plasma using an ultrafast solid-phase extraction/tandem mass spectrometry, which has much faster sample cycle times and similar analytical results to GC/MS. METHOD: Calibration standards, quality controls, and patient samples after addition of busulfan-d4 internal standard were extracted into n-butyl chloride from plasma. The organic fraction was dried and reconstituted in 600 µL of water containing ammonium acetate, trifluoroacetic acid, and formic acid. Sample analysis was performed at a rate of less than 20 seconds per sample using a Rapidfire 300 system coupled to an Agilent 6490 MS/MS using electrospray ionization in positive ion mode. Concentrations were calculated based on a 5-point calibration curve using a 1/x linear curve fit. RESULTS: The analytical method shows excellent precision, sensitivity, and specificity. Minimal ion suppression or enhancement due to the matrix effect was observed. No significant carryover was seen following a sample containing 15,000 ng/mL of busulfan. Seventy-two patient samples were cross-validated with a current GC/MS method. All patient results throughout the analytical range correlated within the acceptance criteria of ±20%. The linear regression demonstrated the following: slope = 1.0067, r = 0.9964, and intercept = -6.2. CONCLUSIONS: A simple, fast, and robust method was developed for the quantitation of busulfan in plasma with solid-phase extraction/tandem mass spectrometry cycle times of <20 seconds per sample.

Pharmacokinetics study of once-daily intravenous busulfan in conditioning regimens for hematopoietic stem cell transplantation.

In Japan, intravenous busulfan (ivBu) is usually given four times per day as an infusion at 0.8 mg/kg over 2 h. However, as this requires a midnight administration, a once-daily infusion of ivBu at 3.2 mg/kg over 3 h has been investigated as a more convenient and safer method. In this study, 20 Japanese patients received once-daily ivBu in conditioning regimens before allogeneic hematopoietic stem cell transplantation (HSCT), and blood samples were obtained just before, and 3, 3.5, 5, 7, 10, and 24 h after the initiation of ivBu infusion. The outcomes of HSCT were evaluated prospectively. The median area under the plasma concentration versus time curve (AUC) of Bu was 5272 µmol × min/L (range 3491-6284 µmol × min/L), and was similar to those in previous once-daily ivBu studies and to the estimated daily AUC in previous 4-times-daily ivBu studies. All of the patients but two, who died early due to infection, achieved neutrophil engraftment at a median of 25 days after transplantation. No patient was diagnosed with veno-occlusive disease according to the criteria established by Jones. No regimen-related toxicity was significantly associated with AUC. In conclusion, once-daily administration of ivBu has a stable pharmacokinetic profile, and was safely performed in Japanese patients.

Pharmacokinetics of treosulfan and its active monoepoxide in pediatric patients after intravenous infusion of high-dose treosulfan prior to HSCT.

Pro-drug treosulfan (TREO) is currently evaluated in randomized phase III clinical trials as a conditioning agent prior to HSCT. In the present paper pharmacokinetics of both TREO and its biologically active monoepoxide (S,S-EBDM) was investigated in pediatric patients for the first time. The studies were carried out in 16 children (median age 7.5 years) undergoing TREO-based preparative regimen prior to HSCT, who received 10, 12 or 14 g/m(2) of the drug as a 1h or 2h intravenous infusion. Plasma concentrations of TREO as well as S,S-EBDM were determined using the validated HPLC-MS/MS method. The changes in S,S-EBDM concentration over time followed TREO levels. The area under the curve (AUC) of TREO was 100-fold higher than AUC of S,S-EBDM. No statistically significant dependency of the dose-normalized AUC of either TREO or S,S-EBDM on the patients' age and body surface area was stated. Moreover, plasma C(max) as well as AUC of S,S-EBDM demonstrated linear correlation with the C(max) and AUC of TREO, respectively. The biological half-lives of TREO and S,S-EBDM were similar. This indicates that S,S-EBDM was completely eliminated from the patients' blood within relatively short time, comparable to TREO.

Effect of age on the pharmacokinetics of busulfan in patients undergoing hematopoietic cell transplantation; an alliance study (CALGB 10503, 19808, and 100103).

PURPOSE: Older patients with acute myeloid leukemia (AML) and myelodysplastic syndrome have often been excluded from myeloablative-conditioning regimens containing busulfan because of non-disease-related morbidity and mortality. We hypothesized that busulfan clearance (BuCL) in older patients (>60 years) would be reduced compared to that in younger patients, potentially explaining observed differences in busulfan tolerability. METHODS: AML patients in three CALGB hematopoietic cell transplantation studies were treated with a conditioning regimen using IV busulfan, dosed at 0.8 mg/kg. Plasma busulfan concentrations were determined by LC-MS and analyzed by non-compartmental methods. BuCL was normalized to actual (ABW), ideal (IBW), or corrected (CBW) body weight (kg). Differences in BuCL between age groups were examined using the Wilcoxon rank sum test. RESULTS: One hundred and eighty-five patients were accrued; 174 provided useable pharmacokinetic data. Twenty-nine patients ≥ 60 years old (median 66; range 60-74) had a significantly higher BuCL versus those <60 years old (median 50; range 18-60): BuCL 236 versus 168 mL/min, p = 0.0002; BuCL/ABW 3.0 versus 2.1 mL/min/kg, p = 0.0001; BuCL/IBW 3.8 versus 2.6 mL/min/kg, p = 0.0035; BuCL/CBW 3.4 versus 2.6 mL/min/kg, p = 0.0005. Inter-patient variability in clearance (CV %) was up to 48 % in both age groups. Phenytoin administration, a potential confounder, did not affect BuCL, regardless of weight normalization (p > 0.34). CONCLUSIONS: Contrary to our hypothesis, BuCL was significantly higher in older patients compared to younger patients in these studies and does not explain the previously reported increase in busulfan toxicity observed in older patients.

The pharmacokinetics and safety of twice daily i.v. BU during conditioning in pediatric allo-SCT recipients.

Intravenous BU divided four times daily (q6 h) has been shown to be safe and effective in pediatric allo-SCT recipients. Though less frequent dosing is desirable, pharmacokinetic (PK) data on twice daily (q12 h) i.v. BU administration in pediatric allo-SCT recipients is limited. We prospectively examined the PK results in a cohort of pediatric allo-SCT recipients receiving i.v. BU q12 h as part of conditioning before allo-SCT. BU levels were obtained after the first dose of conditioning. PK parameter analysis (n=49) yielded the following 95% confidence intervals (CI95): weight-normalized volume of distribution: 0.65-0.73 L/kg; t(1/2): 122-147 min; weight-normalized clearance (CL(n)): 3.4-4.3 mL/min/kg; and area under the curve: 1835-2180 mmol × min/L. From these results, a steady state concentration was calculated with CI95 between 628-746 ng/mL. Comparison between recipients ≤4 vs >4 years old revealed significant differences in t(1/2) (mean: 115 vs 146 min, P=0.008) and CL(n) (mean: 4.4 vs 3.5 mL/min/kg, P=0.038). Intravenous BU q12 h had a comparable PK to i.v. BU q6 h PK seen in the literature, and in pediatric allo-SCT recipients, is a feasible, attractive alternative to i.v. q6h dosing.

Busulfan pharmacokinetics following intravenous and oral dosing regimens in children receiving high-dose myeloablative chemotherapy for high-risk neuroblastoma as part of the HR-NBL-1/SIOPEN trial.

INTRODUCTION: Busulfan is widely used in a neuroblastoma setting, with several studies reporting marked inter-patient variability in busulfan pharmacokinetics and pharmacodynamics. The current study reports on the pharmacokinetics of oral versus intravenous (IV) busulfan in high-risk neuroblastoma patients treated on the European HR-NBL-1/SIOPEN study. METHODS: Busulfan was administered four times daily for 4 days to children aged 0.7-13.1 years, either orally (1.45-1.55 mg/kg) or by the IV route (0.8-1.2mg/kg according to body weight strata). Blood samples were obtained prior to administration, 2, 4, and 6h after the start of administration on dose 1. Busulfan analysis was carried out by gas chromatography-mass spectrometry and data analysed using a NONMEM population pharmacokinetic approach. RESULTS: Busulfan plasma concentrations obtained from 38 patients receiving IV busulfan and 25 patients receiving oral busulfan, were fitted simultaneously using a one-compartment pharmacokinetic model. Lower variability in drug exposure was observed following IV administration, with a mean busulfan area under the plasma concentration versus time curve (AUC) of 1146 ± 187 µM.min (range 838-1622), as compared to 953 ± 290 µM.min (range 434-1427) following oral busulfan. A total of 87% of children treated with IV busulfan achieved AUC values within the target of 900-1500 µM.min versus 56% of patients following oral busulfan. Busulfan AUC values were significantly higher in HR-NBL-1/SIOPEN trial patients who experienced hepatic toxicity or veno-occlusive disease (VOD) (1177 ± 189 µM.min versus 913 ± 256 µM.min; p=0.0086). Further stratification based on route of administration suggested that the incidence of hepatic toxicity was related to both high busulfan AUC and oral drug administration. CONCLUSION: The reduced pharmacokinetic variability and improved control of busulfan AUC observed following IV administration support its utility within the ongoing HR-NBL-1/SIOPEN trial.

Maximally tolerated busulfan systemic exposure in combination with fludarabine as conditioning before allogeneic hematopoietic cell transplantation.

Systemic exposure to high-dose busulfan has been correlated with efficacy and toxicity after hematopoietic cell transplantation for malignancy. We used the area under the concentration-time curve (AUC) to prospectively determine the maximally tolerated systemic exposure to i.v. busulfan when given once daily after fludarabine administered at 40 mg/m(2) for 4 days. Three target AUC levels were planned: 6,000, 7,500, and 9,000 µM-min. Included were patients 16 to 65 years old, with a hematologic malignancy, an HLA A, B, or C, DRB1 8/8 or 7/8 matched donor, Karnofsky performance status ≥70%, and adequate organ function. For level 1 patients, i.v. busulfan doses 1 and 2 were 170 mg/m(2)/day, then doses 3 and 4 were adjusted based on first-dose pharmacokinetic modeling to achieve an average daily AUC of 6,000 µM-min. Doses 1 and 2 for the subsequent cohorts were based on the level 1 data: 180 mg/m(2)/day for AUC 7,500 µM-min (level 2) and 220 mg/m(2)/day for AUC 9,000 µM-min (level 3), with pharmacokinetic targeting for doses 3 and 4. Pharmacokinetic analysis after the last dose showed that 88% of the patients had been exposed to a mean AUC within 10% of the target. Forty patients were treated at level 1, 29 patients at level 2, and three patients at level 3. DLT was veno-occlusive disease of the liver, which occurred in none of 40 patients (0%) at level 1, two of 29 patients (7%) at level 2, and three of three patients (100%) at level 3. Dermatitis (P < .01) and pulmonary toxicity (P = .01) were also increased at higher AUC levels. Level 2 (7,500 µM-min × 4 days) was the maximally tolerated AUC. Within the confines of the trial's small sample size, there was no suggestion that escalating busulfan AUC from 6,000 to 7,500 µM-min × 4 days increased nonrelapse mortality. Assessment of the higher busulfan AUC on relapse prevention requires trials in patients with a homogeneous risk of relapse.

Busulfan and metronidazole: an often forgotten but significant drug interaction.

OBJECTIVE: To report the case of a clinically significant drug interaction between intravenous busulfan and oral metronidazole observed through busulfan therapeutic drug monitoring (TDM). CASE SUMMARY: A 7-year-old boy with a history of myelodysplasia that progressed to acute myeloid leukemia received busulfan with therapeutic drug monitoring (TDM), clofarabine, and thiotepa as a pretransplant conditioning regimen for a cord blood transplant. The patient received metronidazole the day after a busulfan test dose of 0.5 mg/kg was administered. On the day of the first busulfan therapeutic dose, TDM was performed and the clearance of busulfan was significantly decreased by 46%. After 2 doses of busulfan therapy, the course area under the curve was exceeded, requiring discontinuation of busulfan. Metronidazole is not known to affect glutathione or the glutathione S-transferase A1 (GSTA1) enzyme system or cytochrome P450 (CYP) 3A4. DISCUSSION: Busulfan is a bifunctional alkylating agent widely used in pretransplant conditioning regimens in patients undergoing stem cell transplantation for hematologic malignancies. Busulfan metabolism is best described by hepatic conjugation to glutathione by GSTA1, although some CYP-dependent pathways have been described. Currently there is 1 publication describing the drug interaction between oral busulfan and oral metronidazole, in which concomitant use of metronidazole resulted in higher busulfan trough concentrations and higher risk of veno-occlusive disease. Our case represents a possible drug interaction based on the Horn Drug Interaction Probability Scale. CONCLUSIONS: Though the mechanistic basis for this interaction is unknown, the risks and benefits of using metronidazole during and in close proximity to busulfan should be carefully considered and therapeutic alternatives to metronidazole should be used when appropriate.

Safety and efficacy of targeted busulfan therapy in children undergoing myeloablative matched sibling donor BMT for sickle cell disease.

Busulfan influences engraftment and toxicities during hematopoietic stem cell transplantation (HSCT). We report our single-institution experience of targeted busulfan therapy for myeloablative, matched sibling donor (MSD) HSCT for sickle cell disease (SCD) and assess the relationships of busulfan levels to engraftment and toxicities. Twenty-seven patients with SCD underwent MSD HSCT from 1993 to 2007, 25 with busulfan measurements. The conditioning regimen was busulfan (initial dose 0.875 mg/kg for 16 doses), CY and antithymocyte globulin. Busulfan area under curve (AUC) was determined with the first dose, and dose adjustments were made to target the desired AUC range. Median AUC was 963 µmol min/L (range 780-1305 µmol min/L). Engraftment occurred in all cases: 21 (84%) full donor chimerism (> 95% donor cells), 4 (16%) partial donor chimerism. Hepatic veno-occlusive disease (VOD) occurred in 8 (32%) patients. Lower AUC was seen with partial donor chimerism (862 ± 73 µmol min/L) versus full donor chimerism (AUC 1018 ± 122 µmol min/L) (P = 0.022). VOD was not associated with busulfan AUC (P = 0.153). Of 25 patients, 24 survived with median follow-up of 4.9 years. Our experience shows that targeting busulfan AUC above the range used in previous multicenter trials appears safe and may contribute to sustained engraftment in SCD.

Integration of modelling and simulation into the development of intravenous busulfan in paediatrics: an industrial experience.

Busulfan (Bu) is commonly used in preparative conditioning regimen prior to bone marrow transplantation in infants (< 1 year old), children and adolescents (up to 17 years old). The clinical development of an intravenous form of busulfan (Busilvex) was based on pharmacokinetic (PK) modeling and simulation techniques. A retrospective population PK analysis was initially performed from a first study in 24 pediatric patients (0.45-16.7 years old) and a log-linear relationship between body weight and Busilvex clearance was demonstrated with no age-dependency. For an optimal area under the curve (AUC) targeting, a new Bu dosing regimen [i.e. 5 dose levels (0.80 to 1.20 mg/kg) adjusted to 5 discrete weight categories] was developed and assessed through population PK-based simulations. The benefit from this new dosing strategy was validated in a second trial including 55 children (0.30-17.2 years old). This prospective trial confirmed the previous simulations: an efficient therapeutic targeting whatever the patient's age or body weight. Over 80% of the children were within the desired plasma exposure window, and the initial PK model was validated on the confirmatory dataset.

Pharmacokinetics of once-daily IV busulfan as part of pretransplantation preparative regimens: a comparison with an every 6-hour dosing schedule.

In pretransplantation therapy busulfan is typically given every 6 hours. We infused busulfan once daily at 130 mg/m2 for 4 days, performing pharmacokinetic analyses on plasma concentration-time data (n = 60 patients) on days 1, 3, and/or 4. Mean (percent coefficient of variation) maximum concentration, volume of distribution, half-life, and clearance were 3.6 microg/mL (13.8%), 22.6 L/m2 (20.2%), 2.73 hours (27.5%), and 109 mL/min/m2 (26%), respectively. The mean (percent coefficient of variation) and median daily areas under the curve were 4873 (21.8%) and 4871 microM x minute. Intrapatient variability in day-to-day estimated clearance was <20%, without day-to-day drug accumulation. The pharmokinetic parameters were compared with those from 47 patients given intravenous busulfan at approximately 0.8 mg/kg (approximately 32 mg/m2) every 6 hours. We conclude that there is (1) a dose proportionality based on mean and median areas under the curve, (2) unchanged estimated clearance with a 4-fold increase in dose and a 2.5-fold difference in dosing rate, (3) negligible variability in dose-to-dose pharmacokinetics and negligible interdose accumulation with once-daily administration, and (4) no change in pharmokinetic parameter(s) with concomitant use of imidazole antifungals, oral contraceptives, or phenytoin. In summary, intravenous busulfan has highly predictable, linear pharmacokinetics from 32 mg/m2 (approximately 0.8 mg/kg) to 130 mg/m2 (approximately 3.2 mg/kg). Further, once-daily intravenous busulfan dosing is convenient, favoring its more widespread application.

A comparison of the biodistribution and biokinetics of (99m)Tc-anti-CD66 mAb BW 250/183 and (99m)Tc-anti-CD45 mAb YTH 24.5 with regard to suitability for myeloablative radioimmunotherapy.

Radioimmunotherapy (RIT) with radiolabelled monoclonal antibodies (mAbs) is an effective method of achieving myeloablation in leukaemia patients prior to stem cell transplantation (SCT). We wished to compare the approaches of specific binding to leukaemic blasts and non-specific binding to benign red marrow cells, which results in a myeloablative "cross-fire" effect. Therefore, we prospectively evaluated the biodistribution and biokinetics of the anti-CD45 mAb YTH 24.5 and the anti-CD66 mAb BW 250/183 with regard to their suitability for myeloablative RIT. The red marrow selective anti-CD66 mAb BW 250/183 (IgG1) binds to normal granulopoietic cells. In contrast, the anti-CD45 mAb YTH 24.5 (IgG2b) binds to 85-90% of acute leukaemic blasts and almost all haematopoietic white cells. Patients with leukaemic blast infiltration of the marrow <25% and assigned for RIT and SCT were included. Twelve patients (eight male, four female; median age 46+/-7 years) with AML (5), CML (5) or ALL (2) were examined. Both mAbs were labelled with technetium-99m. Within 48 h, 906+/-209 MBq (99m)Tc-anti-CD66 mAb and 760+/-331 MBq (99m)Tc-anti-CD45 mAb were injected consecutively. Scintigraphic and urinary measurements were performed 1, 2, 4 and 24 h after injection. Serum activities were evaluated 2, 5, 10, 15, 30 and 60 min and 2, 4 and 24 h after injection. Compared with the anti-CD45 mAb, the anti-CD66 mAb showed an approximately fourfold higher accumulation in the red marrow, a 2.5-fold lower accumulation in the liver and similar accumulation in the kidneys. The serum activity (% of the injected dose) initially decreased faster for the anti-CD45 mAb but was similar for the two mAbs 24 h after injection: 3.3%+/-1.2% (anti-CD66 mAb) and 2.4%+/-1.1% (anti-CD45 mAb). The cumulated urinary excretion was 17%+/-6.6% (anti-CD66 mAb) and 27.3%+/-7.9% (anti-CD45 mAb) 24 h after application. In these patients with low tumour load, the anti-CD66 mAb BW 250/183 showed more favourable properties in terms of biodistribution and pharmacokinetics. Thus, it appears superior to anti-CD45 mAb YTH 24.5 in selectively increasing the marrow dose and avoiding extramedullary organ toxicity.