Dose Modification Protocol Using Intravenous Busulfan (Busulfex) - Core

Biology of Blood and Marrow Transplantation 10:614-623 (2004) 䊚 2004 American Society for Blood and Marrow Transplantation 1083-8791/04/1009-0004$30.00/0 doi:10.1016/j.bbmt.2004.05.010

Dose Modification Protocol Using Intravenous Busulfan (Busulfex) and Cyclophosphamide Followed by Autologous or Allogeneic Peripheral Blood Stem Cell Transplantation in Patients with Hematologic Malignancies Casey B. Williams,1 Suzanne D. Day,1 Michael D. Reed,2 Edward A. Copelan,3 Thomas Bechtel,3 Helen L. Leather,4 John R. Wingard,5 Brian L. Abbott,1 Sunil Abhyankar,1 Joseph P. McGuirk1 1

Blood and Marrow Transplant Program of the Kansas City Cancer Centers and the Cancer Institute at Saint Luke’s Hospital, Kansas City, Missouri; 2Pharmacology Division, Case Western Reserve University, Cleveland, Ohio; 3Division of Hematology and Oncology, Ohio State University, Columbus, Ohio; 4Department of Pharmacy, University of Florida, Gainesville, Florida; 5Department of Medicine, University of Florida, Gainesville, Florida Correspondence and reprint requests: Casey Williams, Pharm D, BCOP, Kansas City Blood and Marrow Transplant Program, 4320 Wornall, Suite 220, Kansas City, MO 64111 (e-mail: [email protected]). Received October 10, 2003; accepted May 10, 2004

ABSTRACT We evaluated the safety and toxicity through a 5-cohort dose-modification model of once-daily administration of IV busulfan (Bu) in combination with high-dose cyclophosphamide (Cy) as preparative therapy for stem cell transplantation. Twenty-one adult patients with hematologic malignancies were evaluated. Eleven patients underwent autologous and 10 patients underwent HLA-matched sibling allogeneic transplantation. Patients were sequentially enrolled into 5 cohorts. Cohort 1 received intravenous (IV) Bu 1.6 mg/kg every 12 hours for 2 doses and then 0.8 mg/kg every 6 hours for 12 doses; cohort 2 received IV Bu 1.6 mg/kg every 12 hours for 4 doses and then 0.8 mg/kg every 6 hours for 8 doses; cohort 3 received IV Bu 3.2 mg/kg for 1 dose and then 1.6 mg/kg every 12 hours for 2 doses and 0.8 mg/kg every 6 hours for 8 doses; cohort 4 received IV Bu 3.2 mg/kg every 24 hours for 2 doses and then 0.8 mg/kg every 6 hours for 8 doses; and cohort 5 received IV Bu 3.2 mg/kg every 24 hours for 4 doses. In all groups, Bu was administered on day ⴚ7 through day ⴚ4 and was followed at least 6 hours after the last Bu dose by Cy 60 mg/kg daily for 2 doses on days ⴚ3 and ⴚ2. Blood samples were collected for pharmacokinetic analysis on the first and last day of IV Bu administration. All patients were alive and had engrafted at day 30. Five patients developed grade 3 or 4 toxicities. Four patients developed hepatic abnormalities, and 3 exhibited evidence of veno-occlusive disease. Two of 3 patients in cohort 5 with a Bu area under the curve >6000 ␮mol/min developed autopsy-confirmed veno-occlusive disease. Interpatient variability in AUCs was observed in patients within and between cohorts, but no statistically significant interpatient differences were observed in Bu half-life, volume of distribution, clearance, or dose-adjusted area under the curve. Further, minimal variability in Bu pharmacokinetics was observed between the 2 evaluations performed in each patient, thus reflecting the stability of Bu disposition within individual patients. On the basis of the dosing guidelines and schedule outlined in this study, our data suggest that administration of IV Bu 3.2 mg/kg IV every 24 hours for 4 doses in combination with Cy may result in excessive toxicity. © 2004 American Society for Blood and Marrow Transplantation

KEY WORDS Busulfan

●

Once-daily

●

Bone marrow transplant

INTRODUCTION The availability of an intravenous (IV) formulation of busulfan (Bu) combined with the desire to shift care to the outpatient setting led to the investigation of 614

●

Cyclophosphamide

alternative Bu administration schedules other than the 4-times-daily dosing schedule often used. Studies in patients undergoing BMT for hematologic malignancies suggest that IV Bu (IV Busulfex威; ESP Pharma, Edison, NJ) is associated with similar outcomes and

Dose-Modification Protocol for Hematologic Malignancies

toxicities when used instead of oral Bu as a component of the preparative regimen [1-8]. In addition, available information suggests that the incidence of hepatic veno-occlusive disease (VOD) may be lower in patients receiving IV Bu as compared with oral Bu [5-8]. Bu, a bifunctional alkylating agent, is often combined with cyclophosphamide (Cy) for conditioning of patients undergoing allogeneic or autologous hematopoietic stem cell transplantation [1-3,5-15]. The standard oral BuCy2 regimen includes the administration of Bu at a dose and schedule of 1.0 mg/kg every 6 hours for 16 doses and Cy 60 mg/kg daily for 2 doses. Attempts at developing an IV preparation of Bu were initially limited because of the drug’s poor aqueous solubility; however, several formulations have been investigated, including a formulation developed by Andersson et al. [16] that uses dimethyl acetamide and polyethylene glycol (IV Busulfex); it became commercially available in 1999. Data from the phase I trial of Andersson et al. determined that an IV Bu dose of 0.8 mg/kg provided systemic exposure similar to the systemic exposure obtained after a standard oral dose of 1 mg/kg [17]. Pharmacokinetic (PK) data from a phase II trial [8] in which patients with advanced hematologic malignancies were treated with 16 doses of IV Bu 0.8 mg/kg followed by 2 daily IV doses of Cy 60 mg/kg showed that the regimen was well tolerated and demonstrated a more consistent PK profile than that reported with oral Bu. The purpose of this investigation was to evaluate the safety and tolerability of a modified dosing regimen of IV Bu combined with high-dose IV Cy. Through a dose-modification strategy involving 5 unique Bu dose cohorts, we investigated the potential to administer IV Bu once daily for 4 days (cohort 5) in combination with Cy as the preparative regimen before bone marrow transplantation for hematologic malignancies. PK profiles associated with each dosing schedule are reported.

PATIENTS AND METHODS Eligibility Criteria

Patients with hematologic malignancies who were 16 to 60 years old and without a previous stem cell transplantation were eligible if they were in complete remission but had a high risk of relapse or if they had relapsed or refractory disease. Patients older than 60 years of age with a good performance status and minimal comorbidities were considered for enrollment on an individual basis. Patients were required to have a life expectancy longer than 12 weeks and could not be severely limited by concomitant illness. Patients were excluded if they had any of the following: (1) a serum

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creatinine of ⬎2.0 mg/dL, (2) a serum bilirubin ⬎1.5 ⫻ the upper limit of normal, (3) evidence of hepatitis or cirrhosis, (4) abnormal pulmonary function, (5) a cardiac left ventricular ejection fraction ⬍40%, and (6) human immunodeficiency virus seropositivity. Patients receiving autologous transplants must have collected a minimum of 2.5 ⫻ 106 CD34⫹ cells per kilogram during peripheral blood stem cell mobilization. Patients undergoing allogeneic transplantation were required to have granulocyte colonystimulating factor–mobilized peripheral blood progenitor cells or bone marrow from an HLA-matched related donor available. The study protocol was approved by the Institutional Review Board for Human Subject Investigation from each of the participating study sites, and written, informed consent was obtained from each patient. Conditioning Regimen

Patients were hospitalized during IV Bu administration to facilitate observation of toxicities and PK monitoring. Patients were consecutively assigned to dose cohorts 1 through 5. IV Bu was given according to the designated cohort schedule and infusion rate beginning on day ⫺7. Cy 60 mg/kg was given IV over 2 hours for 2 consecutive days beginning on day ⫺3, no sooner than 6 hours after the last IV Bu dose. Doses for both Bu and Cy were based on the lesser of actual or adjusted ideal body weight [18]. Dose-Modification Schedule

Each cohort was to consist of 4 patients. All patients within a cohort were monitored for a minimum of 30 days after stem cell infusion to assess safety and initial efficacy. The last patient within a cohort must have completed the monitoring period of 30 days after stem cell infusion before proceeding to the next cohort. In the event that 1 of the following dose-limiting toxicities occurred within a cohort during the monitoring period, an additional 2 patients were added to the specified cohort before advancing to the next cohort: (1) seizures considered related to Bu; (2) severe VOD, as defined by death due to VOD or lack of resolution or improvement of VOD by day 30; (3) grade 4 gastrointestinal toxicity related to Bu; (4) delayed neutrophil engraftment related to Bu, defined by lack of achievement of absolute neutrophil count ⬎500 by day 28; and (5) an unexpected grade 4 or life-threatening toxicity related to Bu. If no doselimiting toxicity occurred in the 2 additional patients, we advanced to the next Bu dose cohort. If 2 or more dose limiting toxicities occurred within a Bu dose cohort, then subsequent patients were enrolled in the previous cohort. The maximally tolerated IV Bu dosing schedule was then defined as the cohort dose schedule below the cohort in which 2 or more dose 615

C. B. Williams et al.

Table 1. Dosing Schedules* Cohort 1 Day ⴚ7 Day ⴚ6 Day ⴚ5 Day ⴚ4 Cohort 2 Day ⴚ7 Day ⴚ6 Day ⴚ5 Day ⴚ4 Cohort 3 Day ⴚ7 Day ⴚ6 Day ⴚ5 Day ⴚ4 Cohort 4 Day ⴚ7 Day ⴚ6 Day ⴚ5 Day ⴚ4 Cohort 5 Day ⴚ7 Day ⴚ6 Day ⴚ5 Day ⴚ4

1.6 0.8 0.8 0.8

mg/kg mg/kg mg/kg mg/kg

IV IV IV IV

(over (over (over (over

4 2 2 2

h) h) h) h)

q12h ⴛ 2 doses q6h ⴛ 4 doses q6h ⴛ 4 doses q6h ⴛ 4 doses

1.6 1.6 0.8 0.8

mg/kg mg/kg mg/kg mg/kg

IV IV IV IV

(over (over (over (over

2 4 2 2

h) h) h) h)

q12h ⴛ 2 doses q12h ⴛ 2 doses q6h ⴛ 4 doses q6h ⴛ 4 doses

3.2 1.6 0.8 0.8

mg/kg mg/kg mg/kg mg/kg

IV IV IV IV

(over (over (over (over

4 2 2 2

h) h) h) h)

q24h ⴛ 1 dose q12h ⴛ 2 doses q6h ⴛ 4 doses q6h ⴛ 4 doses

3.2 3.2 0.8 0.8

mg/kg mg/kg mg/kg mg/kg

IV IV IV IV

(over (over (over (over

4 4 2 2

h) h) h) h)

q24h ⴛ 1 dose q24h ⴛ 1 dose q6h ⴛ 4 doses q6h ⴛ 4 doses

3.2 3.2 3.2 3.2

mg/kg mg/kg mg/kg mg/kg

IV IV IV IV

(over (over (over (over

4 4 4 4

h) h) h) h)

q24h q24h q24h q24h

ⴛ ⴛ ⴛ ⴛ

1 1 1 1

dose dose dose dose

12h indicates every 12 hours. *Doses are based on the lesser of actual or adjusted body weight. Ideal body weight [18]: male (kg), 56.2 ⫹ (1.41 ⫻ No. inches over 60); female (kg) 53.1 ⫹ (1.36 ⫻ No. inches over 60). Adjusted body weight: 0.25 (total body weight ⫺ ideal body weight) ⫹ ideal body weight.

dose 11 for cohort 1, dose 9 for cohort 2, dose 8 for cohort 3, dose 7 for cohort 4, and dose 4 for cohort 5. The PK parameter estimates for Bu were determined by using standard noncompartmental methods [21] with Kinetica version 4.1 (Innaphase Corp., Champs-sur-Marne, France). For each patient, plasma Bu concentrations were plotted against time on a semilogarithmic scale. The peak Bu plasma concentration and time to peak concentration were determined directly from the plasma concentration/time curves. The area under the curve (AUC) was obtained by using the linear trapezoidal rule up to the final measured concentration and was extrapolated to infinity by using ␤ after the first dose and to the end of the dosing interval (t) under multidose conditions. The elimination half-life (t ⁄ ) was determined from the postdistributive terminal portion of the plasma concentration/time curve. Total body clearance (Cl) was determined with the formula dose/AUC0-infinity after the first dose and dose/AUC0-t under multidose conditions. The apparent steady-state volume of distribution (Vdss) was determined with the following equation: 12

Vdss ⫽ [(dose)(AUMC)]/AUC2 ⫺ [(dose)(T)/(AUC)(2)] where AUMC is the area under the first moment of the concentration/time curve and T is the infusion duration. Sample Preparation

limiting toxicities occurred with at least 6 patients studied. Supportive Care

Phenytoin was administered as seizure prophylaxis before and during Bu treatment in all patients. Mesna, antiemetics, blood products, and other supportive care measures were used according to institutional guidelines and at the discretion of the attending physician as deemed necessary by a patient’s disease history and risk factors. For patients undergoing allogeneic transplantation, cyclosporine and short-course mini-methotrexate were used as graft-versus-host disease prophylaxis [19,20]. PK Analysis

Multiple timed blood samples (5 mL) for Bu PK analysis were obtained from each patient. The time and quantity of samples obtained were dependent on which Bu dose cohort each patient was participating in. The IV Bu dose regimen for each of the 5 dose cohorts is outlined in Table 1. In all cohorts, samples were collected on day ⫺7 and day ⫺4. On day ⫺7, samples were collected around dose 1, regardless of cohort. On day ⫺4, samples were collected around Bu 616

A 0.2-mL plasma sample was added to a borosilicate glass tube containing 0.04 mL of internal standard and vortexed; 0.5 mL of methanol was added and vortexed again for 10 seconds. The samples were derivatized by using a modification of the method of Rifai et al. [22] by adding 0.15 mL of 5% diethyldithiocarbamate and vortexing for 10 seconds. To this sample, 0.5 mL of ultrapure water was added and vortexed for 10 seconds, after which 2 mL of ethyl acetate was added. The tube was covered with aluminum foil and capped, vortexed for 1 minute, and centrifuged at 4000 rpm for 2 minutes. The supernatant was transferred to a clean borosilicate tube with the contents dried under nitrogen at 40°C by using a Zymark Turbo Vap Evaporator (Zymark, Hopkinton, MA), resuspended in 0.05 mL of butanol, and transferred to a clean vial. Subsequently 1 ␮L was injected into a Varian 3400 gas chromatograph (Varian, Walnut Creek, CA) equipped with a thermionic specific detector (nitrogen/phosphorous detector) and an 8100 autosampler. A Varian 1077 split/splitless injector at 270°C and a Restek Cyclosplitter inlet sleeve (Restek, Bellefonte, PA) were used; the injector was operated in the splitless mode. Analysis was performed with a J&W Scientific capillary DB5 mass spectrometry column (30 m ⫻ 0.25 mm) with a film thickness of 0.25

Dose-Modification Protocol for Hematologic Malignancies

␮m (J&W Scientific, Folsom, CA). UHP helium (Matheson Gas Products, Parsippany, NJ) was used as carrier gas at a flow rate of 4.3 mL/min. The thermionic specific detector was set at 280°C with flow rates of 4.6 mL/min for hydrogen and 169 mL/min for air. The initial oven temperature was maintained at 150°C for 1.5 minutes and was then increased 25°C/min to 260°C with a hold time of 2.6 minutes, followed by a second increase of 25°C/min to 280°C with a hold time of 10.3 minutes. Standards were prepared from a stock solution, 2 mg Bu per milliliter of acetone, that was immediately diluted 10:1 in methanol. Bu and sodium diethyldithiocarbamate trihydrate were obtained from Aldrich Chemical Company (St. Louis, MO). Internal standard—1,6-bis-(methane sulfonlyoxy) hexane—was synthesized by a modification of the method of Rifai et al. [22]. Ethyl acetate, methanol, n-butyl alcohol, and acetone were obtained from Honeywell Burdick and Jackson (Muskegon, MI), and all were high-performance liquid chromatography grade. Internal standard (0.05 mg Bu per milliliter methanol) was prepared by the addition of 3.8 mL of methanol to 200 ␮L of stock solution. A 5% diethyldithiocarbamate solution was prepared daily in ultrapure water. Bu analysis in plasma was linear to 5.0 ␮g/mL. The within-day mean coefficient of variation was 1.41%, and the mean SD was 0.017 (n ⫽ 24). For the between-day variance, triplicate plasma standard curves yielded mean correlation coefficients of 0.9991, 0.9993, and 0.9996. The between-day mean coefficient of variation was 2.43%, and the mean SD was 0.045 (n ⫽ 24). Statistical Analysis

PK parameter estimates and demographic data were examined univariately and graphically to determine distributional characteristics. Bu AUC and peak plasma concentration were normalized for each subject by dividing the parameter by the Bu dose per kilogram administered. The effect of cohort and time on these parameters, as well as Cl corrected for weight, was tested by using a mixed model approach that allows for a possible within-subject correlation across time. An interaction term of time and cohort was also added to the model. If the AUCs were proportional to the dose, then one would not expect to see a cohort effect with this analysis. Differences between first-dose and multidose Bu PK parameter estimates were tested as post hoc contrasts in the mixed model. Hepatic VOD Diagnosis and Evaluation

A clinical diagnosis of VOD was made by the treating physician after clinical examination and laboratory findings were analyzed. Diagnosis was based on the criteria of Jones et al. [23] and assigned a severity grade based on the criteria of Bearman et al. [24].

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RESULTS Patient Characteristics

Clinical data are presented on 21 patients with hematologic malignancies treated at 3 institutions between August 2000 and September 2002. Patient characteristics are listed in Table 2. The median age was 47 years (range, 26-66 years), and there were 12 men and 9 women. Eleven patients underwent autologous transplantation: 8 for non-Hodgkin lymphoma, 1 each for acute myelogenous leukemia (AML), Hodgkin disease, and multiple myeloma. Ten patients underwent allogeneic transplantation: 3 for non-Hodgkin lymphoma, 3 for chronic myelogenous leukemia (CML), 2 for myelodysplastic syndrome (MDS), 1 for AML, and 1 for myeloproliferative disease. Five patients were in complete remission at the time of transplantation. Fifteen patients (71%) had received at least 2 therapies before transplantation, and 9 patients had relapsed or refractory disease at the time of transplantation. The 3 CML patients were in chronic phase, and 2 patients were newly diagnosed with MDS and myeloproliferative disease. The patient with multiple myeloma had stable disease. All patients were alive at day 30. Neutrophil engraftment (absolute neutrophil count ⬎500/␮L) occurred at a median of 14 days (14 days for autologous and 15 days for allogeneic transplantations). The median time to a sustained platelet count of ⬎20000/␮L was 19 days (20 days for autologous and 19 days for allogeneic transplantations). Three patients received granulocyte colony-stimulating factor to speed up neutrophil engraftment. One patient with chronic phase CML initially engrafted platelets on day 0 (platelet nadir ⬎30000), on the basis of the International Bone Marrow Transplant Registry definition of engraftment [25], but later the platelet count decreased, and the patient was transfusion dependent starting on day 25. The patient later died from complications related to the development of VOD. Busulfan Pharmacokinetics

The results of the Bu PK evaluation are shown in Table 3. Interpatient variability in Bu disposition was observed for the Bu PK parameter estimates t ⁄ , volume of distribution, Cl, and dose-adjusted AUC. This variability in Bu disposition parameters was observed between patients within the same dose cohort as well as between patients in each of the 5 dose cohorts. However, no statistically significant differences in Bu t ⁄ , volume of distribution, Cl, or dose-adjusted AUC were observed between dose cohorts. Although a large degree of interpatient variability was observed in Bu disposition, intrapatient Bu PK remained relatively constant between the first and second PK analysis for individual pa12

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Table 2. Patient Characteristics Patient No. Cohort 1 01-001 01-002 01-103 02-104 Cohort 2 02-201 01-202 03-203 01-204 Cohort 3 01-301 03-302 02-303 02-304 Cohort 4 01-401 03-402 03-403 02-404 02-405 02-406 Cohort 5 02-501 02-502 01-503

Age (y)

Disease

Pre-BMT Status

Type of BMT

26 40 52 66

NHL AML MDS NHL

Primary refractory CR1 CMML First relapse

Auto PBSCT Auto PBSCT Allo PBSCT Auto PBSCT

45 59 55 30

MM NHL AML HD

Stable disease CR1 Primary refractory Second relapse

Auto PBSCT Auto PBSCT Allo PBSCT Auto PBSCT

29 61 49 46

NHL NHL NHL CML

CR1 CR3 CR2 First chronic phase

Auto PBSCT Auto PBSCT Allo PBSCT Allo PBSCT

39 64 51 59 48 46

MPD NHL NHL NHL CML NHL

New diagnosis Primary refractory CR2 Relapsed refractory First chronic phase Primary refractory

Allo PBSCT Auto PBSCT Auto PBSCT Allo PBSCT Allo PBSCT Allo PBSCT

46 33 52

MDS CML NHL

New diagnosis First chronic phase Relapsed refractory

Allo PBSCT Allo PBSCT Auto PBSCT

AML indicates acute myelogenous leukemia; Allo, allogeneic; Auto, autologous; CML, chronic myelogenous leukemia; CR1, first complete remission; CR2, second complete remission; CR3, third complete remission; HD, Hodgkin disease; MDS, myelodysplastic syndrome; MM, multiple myeloma; MPD, myeloproliferative disease; NHL, non-Hodgkin lymphoma; PBSCT, peripheral blood stem cell transplantation; Allo, allogeneic; Auto, autologous; CMML, chronic myelomonocytic leukemia; BMT, bone marrow transplantation.

tients (data not shown). With the exception of AUC in cohort 5, no relationship was observed between Bu PK parameter estimates and patient toxicity. As expected, and reflecting the dose administered, the 3 patients enrolled in cohort 5 had the greatest Bu AUC. In cohorts 3, 4, and 5, a total of 7 patients had Bu AUC ⬎5000 ␮mol/min, and 5 patients exhibited no significant toxicities. Toxicity

Most toxicities were grade 1 and 2, including nausea, vomiting, diarrhea, fatigue, and mucositis. Five patients developed grade 3 or greater toxicities, 3 of which resulted in death. One patient had a seizure assumed to be from herpetic encephalitis and subsequently developed complications relating to toxic epidermal necrolysis; this patient died on day 40. Four patients developed hepatic abnormalities, and 3 exhibited evidence of VOD. Of these 4 patients, the only patient in the group who was not diagnosed with VOD was enrolled in cohort 4. This patient (maximum Bu AUC, 6272 ␮mol/min) developed biopsy-confirmed drug-induced hepatitis on day 22, which resulted in a maximum aspartate aminotransferase level of 1332 U/L. Of the 3 patients with VOD, 1 patient enrolled in cohort 2 618

developed moderate clinical VOD on day 18 (maximum total bilirubin, 18 mg/dL; maximum Bu AUC, 2062 ␮mol/min), which resolved without treatment. The remaining 2 cases of VOD occurred in patients enrolled in cohort 5. One patient (maximum Bu AUC, 6380 ␮mol/min) with VOD— based on a maximum total bilirubin of 32.7 mg/dL, jaundice, ascites, weight gain, and right upper quadrant pain—was diagnosed with VOD on day 40 and died on day 51. Autopsy and liver biopsy results confirmed the diagnosis of VOD. The other cohort 5 patient (maximum Bu AUC, 6198 Mol-min) was diagnosed as having moderate VOD on day 17. This was further defined as severe VOD because of a lack of resolution by day 30. The same patient also experienced a grade 3 paralytic ileus and later died. Five patients had a measured Bu AUC ⬎6000 ␮mol/min. Three of the patients were in cohorts 3 and 4, in which the AUC was the highest after day 1 of Bu. The remaining 2 patients were in cohort 5, in which the AUC was highest on day 4 of Bu. Both patients in cohort 5 developed VOD, whereas the other 3 patients did not. In contrast, the patient in cohort 5 who did not develop VOD had Bu AUCs of 4573 ␮mol/min on day 1 and 5391 ␮mol/min on day 4 (Table 4).

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AUC ratio Total mean AUC (␮m/min)

Data are presented as the median (range). AUC indicates area under the busulfan concentration curve; CI ⫽ busulfan body clearance; Cmax ⫽ maximal plasma busulfan concentration; cor ⫽ pharmacokinetic parameter corrected for dose administered; Tmax ⫽ time to maximal plasma busulfan concentration; t1⁄2 ⫽ elimination half-life; Vd ⫽ volume of distribution; T1 ⫽ sample 1; T2 ⫽ sample 2.

3.3 (2.7-3.5) 2.9 (2.7-3.9) 1.0 (0.8-1.1) 0.9 (0.8-1.2) 4.1 (4.1-4.2) 3.9 (3.3-4.0) 3.0 (2.6-3.1) 2.9 (2.3-3.6) 0.4 (0.36-0.6) 2.2 (1.9-2.3) 1.8 (1.6-2.0) 5127.5 6197.9 (4572.9-5410.4) (5391.1-6380.4) 1599 1932.3 (1423.3-1686.8) (1678-1989.6) 0.9 (0.8-0.9) 20 147 2.8 (2.1-3.8) 1.5 (1.0-2.0) 0.87 (0.7-1.2) 1.9 (1.2-2.5) 3.9 (3.7-4.1) 2.0 (1.7-2.5) 3.3 (2.5-4.3) 2.9 (1.8-4.1) 0.66 (0.49-0.79) 0.5 (0.4-0.74) 2.2 (1.3-3.7) 2.5 (1.1-3.7) 4650.2 1125.6 (2999-6634.4) (801.1-1869) 1453.9 1407 (941-2071.7) (997.4-2343.2) 4.0 (3.6-4.6) 19 736 3.3 (2.8-3.5) 1.4 (1.2-1.7) 1.03 (1.5-2.1) 1.8 (1.5-2.1) 4.0 (3.9-4.0) 2.0 (1.5-2.2) 3.0 (2.6-3.5) 2.3 (2.0-3.3) 0.54 (0.49-0.55) 0.45 (0.35-0.63) 2.0 (1.8-2.5) 1.9 (1.7-3.0) 4947.1 1360.1 (4767.4-6027.1) (1076.8-1373.7) 1550.4 1701.6 (1492-1882.1) (1355.9-1722.3) 4.0 (3.5-4.7) 20 685 1.7 (1.7-2.1) 1.2 (1.1-1.4) 1.1 (1.04-1.3) 1.5 (1.4-1.7) 2.0 (1.6-2.1) 2.1 (2-2.1) 2.9 (2.7-3) 2.8 (2.4-2.9) 0.59 (0.49-0.61) 0.6 (0.43-0.68) 2.5 (1.9-2.7) 2.6 (1.8-3) 2261.7 1121.6 (2062.2-2421.3) (955.5-1144.5) 1417.3 1387.8 (1281.1-1518.4) (1187.1-1424.4) 2.1 (1.97-2.2) 17 693 1.5 (1.3-2) 1.3 (0.95-2.2) 0.9 (0.8-1.3) 1.1 (1.0-3.0) 3.5 (3.4-3.8) 2.0 (1.5-2.1) 2.7 (1.9-3.6) 3.1 (2.3-4.4) 0.66 (0.47-0.67) 0.6 (0.51-0.73) 2.5 (2.1-4) 2.3 (1.4-3.7) 2142.5 1209.6 (1626.3-3193.5) (881.1-2522.8) 1335.3 1507.7 (1010.6-1996) (1123.8-3153.5) 1.8 (1.3-1.9) 22 021 Cmax (␮g/mL) Cmaxcor (␮g/mL) Tmax (h) t1⁄2 (h) Vd (L/kg) Cl (mL/min/kg) AUC (␮mol/min) AUCcor

T2 T1 T2 T1 T2 T1 T2 T1 T1

T2

Dose Cohort 2 (n ⴝ 4) Dose Cohort 1 (n ⴝ 4)

Pharmacokinetic Parameter Estimate

Table 3. Pharmacokinetic Profile of Intravenous Busulfan

Dose Cohort 3 (n ⴝ 4)

Dose Cohort 4 (n ⴝ 6)

Dose Cohort 5 (n ⴝ 3)

Dose-Modification Protocol for Hematologic Malignancies

DISCUSSION Although the standard oral BuCy2 regimen is effective, it is often not well tolerated. Oral Bu is available in the United States only as a 2-mg tablet. This requires patients to ingest large numbers of pills with each dose. Administration can be eased by repackaging the tablets, but ingestion remains difficult, particularly if the patient is nauseated or has difficulty swallowing. The PK profile of orally administered Bu demonstrates wide interpatient and intrapatient variability due to age-related differences, alterations in absorption, circadian variations, drug-drug and drugfood interactions, and patient-specific parameters [2631]. PK studies with oral Bu demonstrate variations as high as 50% in calculated PK parameter estimates and may not be calculable in up to 20% of patients because of slow absorption, delayed elimination, or both [2628]. Although the practice of first-dose Bu PK analysis directing subsequent dosing for an individual treatment course is routine at many centers, common problems with sampling and monitoring of oral Bu underscore the need for alternate methods of drug delivery that provide more consistent and reliable Bu disposition and systemic exposure. Initial BuCy regimens required Bu to be administered 4 times daily. Similar to the oral Bu dosing strategies, initial IV Bu studies used the same dosing strategy (ie, every-6-hour dosing) and have demonstrated predictable and consistent PK profiles with acceptable toxicity [1-3,5-8,17]. The data presented here with IV Bu dosing across the range studied confirm the overall intrapatient consistency and predictability of IV Bu PK. Once-daily IV Bu dosing would seem to be more convenient for the patient, possibly allowing for outpatient transplantations, and could be equally effective if overall Bu exposure were comparable to standard oral Bu dosing regimens. The primary objective of this study was to assess the safety, by using a dose-modification cohort schedule, of once-daily IV Bu in combination with highdose IV Cy as the preparative regimen for patients undergoing autologous or allogeneic stem cell transplantation. We found that once-daily administration of high-dose IV Bu in combination with Cy was associated with an increased risk of liver toxicity and the development of VOD. Patients in cohorts that used conventional every-6-hour IV Bu dosing after the investigational portion of the dosing regimen tolerated the preparative regimen better. However, on the basis of our study protocol and the apparently disproportionate increase in observed adverse effects (VOD) for cohort 5 patients, we believed it prudent and appropriate after enrolling 3 patients to discontinue enrollment. Data from PK evaluations after oral Bu given every 6 hours indicated that increased Bu exposure 619

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Table 4. Treatment-Related Risk Factors for the Development of VOD

Patent No. Cohort 1 01-001 01-002 01-103 02-104 Cohort 2 02-201 01-202 03-203 01-204 Cohort 3 01-301 03-302 02-303 02-304 Cohort 4 01-401 03-402 03-403 02-404 02-405 02-406 Cohort 5 02-501 02-502 01-503

Pre-BMT Treatment(s) ABVD ⴛ 8 cycles, ESHAP ⴛ 2 cycles 3-drug induction and Cy/VP/G-CSF mobilization No prior treatment CHOP ⴛ 8 cycles, MINE ⴛ 3 cycles

Time Interval between Last Dose of Bu and First Dose of Cy

9h 8h 9h 8h

VAD ⴛ 4 cycles, Cy/G-CSF mobilization CHOP ⴛ 6 cycles Ida/ARA-C induction and high-dose ARA-C consolidation ⴛ 1 ABVD ⴛ 10 cycles, ESHAP ⴛ 2 cycles, Cy/GCSF mobilization, XRT to spine and mediastinum

8h 8h 10 h 8h

CHOP ⴛ 4 cycles, RICE ⴛ 2 cycles M-BACOD ⴛ 10 cycles, CHOP ⴛ 10 cycles CHOP ⴛ 4 cycles, MINE ⴛ 6 cycles, rituximab ⴛ 4 cycles, XRT to abdomen and pelvis No prior treatment

8h 7h 8.5 h 8h

Local XRT Left nephrectomy and adrenalectomy, splenectomy, CHOP ⴛ 4 cycles, ESHAP ⴛ 2 cycles, rituximab ⴛ 5 cycles, Cy/VP mobilization CVP ⴛ 10 cycles, rituximab ⴛ 8 cycles, FNP ⴛ 2 cycles CVP ⴛ 4 cycles, fludarabine ⴛ 12 cycles, DHAP ⴛ 2 cycles, rituximab ⴛ 5 cycles, CHOP ⴛ 3 cycles Hydroxyurea ⴛ 2 mo R-CHOP ⴛ 7 cycles, ESHAP ⴛ 2 cycles, XRT to spine

8h 4.5 h

Mitomycin/5-FU ⴛ 2 cycles, XRT to pelvis, abdominal surgery Imatinib ⴛ 2 mo R-CHOP ⴛ 8 cycles and Cy/VP/G-CSF mobilization

5h 8h 8h 8h 23.5 h 20 h 20 h

G-CSF indicates granulocyte colony-stimulating factor; XRT, radiotherapy; 5-FU, 5-fluorouracil; BMT, bone marrow transplantation; ABVD, doxorubicin, bleomycin, vinblastine, dacarbazine; ESHAP, etoposide, methylprednisolone, cytarabine, cisplatin; Cy/VP/G-CSF, cyclophosphamide, etoposide, G-CSF; R-CHOP, cyclophosphamide, doxorubicin, vincristine, prednisone, rituximab; MINE, mesna, ifosfamide, mitoxantrone, etoposide; VAD, vincristine, doxorubicin, dexamethasone; M-BACOD, methotrexate, bleomycin, doxorubicin, cyclophosphamide, vincristine, dexamethasone; RICE, rituximab, ifosfamide, carboplatin, etoposide; Ida/ARA-C, idarubicin, cytarabine; ARA-C, cytarabine; CVP, cyclophosphamide, vincristine, prednisone; FNP, fludarabine, mitoxantrone, prednisone; DHAP, dexamethasone, cytarabine, cisplatin.

was associated with an increased risk for VOD and also with other regimen-related toxicities [30-35]. Copelan et al. [30,36] demonstrated that patients who had received more extensive chemotherapy before transplant were at greater risk for the development of VOD as a result of having higher Bu AUC. Patients receiving antileukemic therapy (induction/consolidation) before allogeneic bone marrow transplantation also showed a greater chance of developing severe VOD than patients without therapy before transplantation [37]. This study was not designed to examine or correlate pretransplantation treatment and risk of developing VOD. However, patients who developed hepatic abnormalities, VOD, or both had at least 1 risk factor (heavy pretreatment; induction/consolidation for leukemia), as reported previously [30-37]. Excessive systemic exposure to Bu has been associated with higher morbidity and mortality [36]. In this study, dose cohorts 1 through 4 received higher initial doses of IV Bu; subsequent doses were consis620

tent with conventional Bu dosing. The observed incidence of VOD and other toxicities in these first 4 dose cohorts was similar to what has been previously published [5-8,17]. In contrast, 2 of 3 patients enrolled in the cohort receiving 4 once-daily doses of IV Bu developed severe VOD and died from regimen-related toxicity. In cohort 5, exposure to high Bu plasma concentrations was prolonged, as demonstrated by the increased AUC concentrations on day ⫺4 (dose 4) as compared with day ⫺7 (dose 1). However, total Bu exposure between cohorts was not significantly different. A series of recently published articles [4-7] presented the clinical and pharmacologic experience of IV Bu administered in combination with either Cy or fludarabine. Studies by Russell et al. [4] and Fernandez et al. [6] reported results with once-daily IV Bu. The first study reported the results observed in 70 patients treated concurrently with once-daily IV Bu and fludarabine. Patients were dosed on the basis of ideal

Dose-Modification Protocol for Hematologic Malignancies

body weight, and the IV Bu infusion was given over 3 hours. The investigators performed a detailed PK analysis in 12 patients; results showed remarkable consistency among patients, with no significant differences in PK parameters between the first and fourth doses. No patient developed VOD, but 62 (88%) of 70 patients had transient bilirubin increases. Overall, the combination of IV Bu and fludarabine seemed to be well tolerated. An article by de Lima et al. [38] describes the results of using once-daily IV Bu in combination with fludarabine in 96 patients with either AML or MDS. Only 2 cases of reversible VOD are reported. PK analysis showed that the once-daily IV Bu was cleared in less than 24 hours without drug accumulation, which is supported by our results. Fernandez et al. [6] reported the results of 12 patients treated with the combination of IV Bu and Cy as preparative therapy. Six patients received twicedaily IV Bu 1.6 mg/kg per dose for 8 doses, and the other 6 patients received once-daily IV Bu 3.2 mg/kg per dose for 4 doses. All doses were infused over 4 hours and were based on actual body weight, with the exception of 2 patients who received reduced doses because of obesity. Hepatic abnormalities were seen in 2 patients; 1 of these patients developed VOD on day 23. The development of VOD in this patient was attributed to the administration of medroxyprogesterone acetate; the VOD resolved by day 43 after discontinuation of the drug. PK analysis demonstrated highly consistent and reproducible Bu PK parameters in both cohorts. The inconsistency between our outcomes and the outcomes reported by Russell et al. [4], de Lima et al. [38], and Fernandez et al. [6] may be explained by several factors. One possible explanation is a loss of linear Bu elimination in the patients receiving oncedaily dosing, with resulting increased Bu exposure and toxicity. Patients in cohort 5 seemed to show decreased Bu Cl and drug accumulation from the first dose to the fourth dose. However, when AUC is corrected for dose administered and allowing for usual interpatient variability, no statistically significant conclusions can be made. Another possible explanation is the potential additive toxicity from the combination of Bu and Cy. Cy is already known to cause VOD [23,39], and the risk of VOD is of particular concern when Bu is used in combination. McDonald et al. [39] found a strong correlation between blood levels of various Cy metabolites and VOD. Hassan et al. [40] showed that the metabolism of Cy when used in combination with oral Bu greatly influenced toxicity and outcome. When doses of Cy were given within 24 hours of the last dose of oral Bu, prolonged exposure and decreased Cl of Cy were observed. The authors concluded that the hepatic de-

BB&MT

pletion of glutathione-S-transferase by Bu negatively influences the PKs of Cy and ultimately leads to increased toxicity. In this study, all patients were required to receive at least a 6-hour interval between the last dose of Bu and the first dose of Cy, depending on the cohort. Two patients received the first dose of Cy without waiting the entire 6 hours. This coincided with druginduced hepatitis in 1 patient. This patient received the first dose of Cy 4.5 hours after the last dose of Bu. In cohort 5, in which 2 of 3 patients died as a result of complications related to VOD, all 3 patients received the first dose of Cy without waiting a full 24 hours. A third possible explanation is that pretransplantation therapy significantly influenced outcomes in heavily pretreated patients. No patient received medroxyprogesterone acetate or gemtuzumab ozogamicin, which have both previously been documented to increase the risk of developing hepatic VOD [6,41]. Fifteen (71%) of 21 patients were moderately to heavily treated before transplantation. Four patients (19%) received 4 or more prior therapies. Of the 5 patients who developed grade 3 or greater toxicities, 3 were considered heavily pretreated. Multiple factors likely influenced the observed outcomes in this study, most notably treatment before transplantation and the dosing interval between Bu and Cy. All of the patients who developed grade 3 or greater toxicities were either pretreated, received Cy earlier than directed after the final dose of Bu, or both. Our data suggest that the administration of IV Bu 3.2 mg/kg every 24 hours for 4 doses in combination with Cy may result in excessive toxicity, presumably because of increased Bu exposure. It seems probable that the observed intolerance was augmented by the administration of Cy, but the current data do not permit such analysis. In contrast, it seems that the once-daily administration of IV Bu in combination with fludarabine is well tolerated [4,38]. The combination of once-daily IV Bu and Cy as preparative therapy for transplantation should be done with caution and is not recommended unless it is part of a clinical trial. Future studies examining once-daily IV Bu dosing in combination with Cy should evaluate increasing the dosing interval between Bu and Cy to at least 24 hours and potentially targeting lower Bu AUCs to improve outcomes and patient tolerability.

ACKNOWLEDGMENTS The authors thank Jami Niehus, RN, Marcia Jacobson, RN, Diane Scholl, RN, Becky Whittaker, RN, Renee Boyette, RN, Stephanie Picken, RN, and Patty Gerken, RN, FNP, for their outstanding contributions to our research efforts. We also thank Teresa Maag for exemplary administrative support. IV 621

C. B. Williams et al.

Busulfex was provided and the investigation was supported in part by an unrestricted grant from Orphan Medical.

13.

REFERENCES 1. Andersson BS, McWilliams K, Tran H, et al. IV busulfan, cyclophosphamide (BuCy) and allogeneic hematopoietic stem cells (BMT) for chronic myeloid leukemia (CML). Blood. 1998; 92(suppl 1): (abstr. 1168). 2. Kashyap A, Forman S, Cagnoni P, et al. Intravenous busulfan (Busulfex威)/Cytoxan (Cy) preparative regimen for allogeneic (allo) and autologous (auto) hematopoietic stem cell transplantation (BMT) is well tolerated by patients over 50 years of age. Blood. 1998;92(suppl 1):.(abstr. 515) 3. Vaughan WP, Cagnoni P, Fernandez H, et al. Decreased incidence of and risk factors for hepatic veno-occlusive disease with an IV busulfan (bu) containing preparative regimen for hematopoietic stem cell transplantation (HSCT). Blood. 1998; 92(suppl 1): (abstr. 2121). 4. Russell J, Tran H, Quinlan D, et al. Once-daily intravenous busulfan given with fludarabine as conditioning for allogeneic stem cell transplantation: study of pharmacokinetics and early clinical outcomes. Biol Blood Marrow Transplant. 2002;9:468476. 5. Andersson B, Thall P, Madden T, et al. Busulfan systemic exposure relative to regimen-related toxicity and acute graftversus-host disease: defining a therapeutic window for IV BuCy2 in chronic myelogenous leukemia. Biol Blood Marrow Transplant. 2002;9:477-485. 6. Fernandez H, Tran H, Albrecht F, et al. Evaluation of safety and pharmacokinetics of administering intravenous busulfan in a twice-daily or daily schedule in patients with advanced hematologic malignant disease undergoing stem cell transplantation. Biol Blood Marrow Transplant. 2002;9:486-492. 7. Kashyap A, Wingard J, Cagnoni P, et al. Intravenous versus oral busulfan as part of a busulfan/cyclophosphamide preparative regimen for allogeneic hematopoietic stem cell transplantation: decreased incidence of hepatic veno-occlusive disease (HVOD), HVOD-related mortality, and overall 100-day mortality. Biol Blood Marrow Transplant. 2002;9:493-500. 8. Andersson BS, Ashwin K, Gian V, et al. Conditioning therapy with intravenous busulfan and cyclophosphamide (IV BuCy2) for hematological malignancy prior to allogeneic stem cell transplantation: a phase II study. Biol Blood Marrow Transplant. 2002;8:145-154. 9. Santos GW, Tutschka PJ, Brookmeyer R, et al. Marrow transplantation for acute nonlymphocytic leukemia after treatment with busulfan and cyclophosphamide. N Engl J Med. 1983;309: 1347-1353. 10. Tutschka PJ, Copelan EA, Klein JP. Bone marrow transplantation for leukemia following a new busulfan and cyclophosphamide Regimen. Blood. 1987;70:1382-1388. 11. Geller RB, Saral R, Piantadosi S, et al. Allogeneic bone marrow transplantation after high-dose busulfan and cyclophosphamide in patients with acute nonlymphocytic leukemia. Blood. 1989; 73:2209-2218. 12. Weaver CH, Schwartzberg L, Rhinehart S, et al. High-dose chemotherapy with BuCY or BEAC and unpurged peripheral blood stem cell infusion in patients with low-grade non622

14.

15.

16.

17.

18. 19.

20.

21. 22.

23.

24.

25. 26.

27.

28.

Hodgkin’s lymphoma. Bone Marrow Transplant. 1998;21:383389. Ringden O, Labopin M, Tura S, et al. A comparison of busulfan versus total body irradiation combined with cyclophosphamide as conditioning for autograft or allograft bone marrow transplantation in patients with acute leukemia. Acute leukemia working party of the European Group for Blood and Marrow Transplantation (EBMT). Br J Haematol. 1996;93:637-645. Devergie A, Blaise D, Attal M, et al. Allogeneic bone marrow transplantation for chronic myeloid leukemia in first chronic phase: a randomized trial of busulfan-cytoxan versus cytoxantotal body irradiation as preparative regimen—a report from the French Society of Bone Marrow Graft (SFGM). Blood. 1995;85:2263-2268. Blume KG, Kopecky KJ, Henslee-Downey JP, et al. A prospective randomized comparison of total body irradiation-etoposide versus busulfan/cyclophosphamide as preparative regimens for bone marrow transplant in patients with leukemia who were not in first remission: a Southwest Oncology Group study. Blood. 1993;81:2187-2193. Andersson BS, Bhagwatar H, Chow D. Parenteral busulfan for treatment of malignant disease. US patents 5,430,057 (1995) and 5,559,148 (1996). Andersson BS, Madden T, Tran HT, et al. Acute safety and pharmacokinetics of intravenous busulfan when used with oral busulfan and cyclophosphamide as pre-transplantation conditioning therapy: a phase I study. Biol Blood Marrow Transplant. 2000;6:548-554. Miller DR. Determining Ideal Body Weight and Mass. Am J Hosp Pharm. 1983;40:1622. [letter] Storb R, Deeg HJ, Whitehead J, et al. Methotrexate and cyclosporine compared with cyclosporine alone for prophylaxis of acute graft versus host disease after marrow transplantation for leukemia. N Engl J Med. 1986;314:729-735. Przepiorka D, Khouri I, Ippoliti C, et al. Tacrolimus and minidose methotrexate for prevention of acute graft-versushost disease after HLA-mismatched marrow or blood stem cell transplantation. Bone Marrow Transplant. 1999;24:763-768. Gibaldi M, Perrier D. Pharmacokinetics. Second Edition. New York 409-417: Marcel Dekker; 1982. Rifai N, Sakanoto M, Lafi M, Guinan E. Measurement of plasma busulfan concentration by high-performance liquid chromatography with ultraviolet detection. Ther Drug Monit. 1997;19:169-174. Jones RJ, Lee KS, Beschorner WE, et al. Venoocclusive disease of the liver following bone marrow transplantation. Transplantation. 1987;44:778-783. Bearman SI, Anderson GL, Mori M, et al. Venoocclusive disease of the liver: development of a model for predicting fatal outcomes after marrow transplantation. J Clin Oncol. 1993;9: 1729-1736. IBMTR Registration Manual. International Bone Marrow Transplant Registry, 2001. Hassan M, Ehrsson H, Ljungman P. Aspects concerning busulfan pharmacokinetics and bioavailability. Leuk Lymphoma. 1996; 22:395-407. Hassan M, Oberg G, Ehrsson H, et al. Pharmacokinetics and metabolic studies of high-dose busulphan in adults. Eur J Clin Pharmacol. 1989;36:525-530. Hassan M, Oberg G, Bekassy AN, et al. Pharmacokinetics of high-dose busulphan in relation to age and chronopharmacology. Cancer Chemother Pharmacol. 1991;28:130-134.

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29. Grochow LB. Busulfan disposition: the role of therapeutic monitoring in bone marrow transplantation induction regimens. Semin Oncol. 1993;20(suppl 4):18-25. 30. Copelan EA, Bechtel TP, Avalos BR, et al. Busulfan levels are influenced by prior treatment and are associated with hepatic veno-occlusive disease and early mortality but not with delayed complications following marrow transplantation. Bone Marrow Transplant. 2001;27:1121-1124. 31. Dix SP, Wingard JR, Mullins RE, et al. Association of busulfan area under the curve with veno-occlusive disease following BMT. Bone Marrow Transplant. 1996;17:225-230. 32. Grochow LB, Jones RJ, Brundett RB, et al. Pharmacokinetics of high-dose busulfan: correlation with veno-occlusive disease in patients undergoing bone marrow transplantation. Cancer Chemother Pharmacol. 1989;25:55-61. 33. Slattery JT, Sanders JE, Buckner CD, et al. Graft-rejection and toxicity following bone marrow transplantation in relation to busulfan pharmacokinetics. Bone Marrow Transplant. 1995;16: 31-42. 34. Ljungman P, Hassan M, Bekassy AN, et al. High busulfan concentrations are associated with increased transplant-related mortality in allogeneic bone marrow transplant patients. Bone Marrow Transplant. 1997;20:909-913. 35. Slattery JT, Clift RA, Buckner CD, et al. Marrow transplantation for chronic myeloid leukemia: the influence of plasma busulfan levels on the outcome of transplantation. Blood. 1997; 89:3055-3060. 36. Copelan EA, Penza SL, Theil KS, et al. The influence of

BB&MT

37.

38.

39.

40.

41.

early transplantation, age, GVHD prevention regimen, and other factors on outcome of allogeneic transplantation for CML following BuCy. Bone Marrow Transplant. 2000;26:10371043. Copelan EA, Penza SL, Elder PJ, et al. Analysis of prognostic factors for allogeneic marrow transplantation following busulfan and cyclophosphamide in myelodysplastic syndrome and after leukemic transformation. Bone Marrow Transplant. 2000; 25:1219-1222. de Lima M, Couriel D, Thall PF, et al. Once daily intravenous busulfan and fludarabine: clinical and pharmacokinetic results of a myeloablative, reduced toxicity conditioning regimen for allogeneic stem cell transplantation in AML and MDS. Blood. In press. Hassan M, Ljungman P, Ringden O, et al. The effect of busulphan on the pharmacokinetics of cyclophosphamide and its 4-hydroxy metabolite: time interval influence on therapeutic efficacy and therapy-related toxicity. Bone Marrow Transplant. 2000;25:915-924. McDonald GB, Slattery JT, Bouvier ME, et al. Cyclophosphamide metabolism, liver toxicity, and mortality following hematopoietic stem cell transplantation. Blood. 2003;101:20432048. Wadleigh M, Richardson PG, Zahreih D, et al. Prior gemtuzumab ozogamicin exposure significantly increases the risk of veno-occlusive disease in patients who undergo myeloablative allogeneic stem cell transplantation. Blood. 2003;102:15781582.

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