Drug: Busulfex

Busulfan is a bifunctional alkylating agent known chemically as 1,4-butanediol, dimethanesulfonate. BUSULFEX® (busulfan) Injection is intended for intravenous administration. It is supplied as a clear, colorless, sterile, solution in 10 mL single use vials. Each vial of BUSULFEX contains 60 mg (6 mg/mL) of busulfan, the active ingredient, a white crystalline powder with a molecular formula of CH3SO2O(CH2)4OSO2CH3 and a molecular weight of 246 g/mole. Busulfan has the following chemical structure: Busulfan is dissolved in N,N-dimethylacetamide (DMA), 3.3 mL and Polyethylene Glycol 400, NF 6.7 mL. The solubility of busulfan in water is 0.1 g per L and the pH of BUSULFEX diluted to approximately 0.5 mg per mL busulfan in 0.9% Sodium Chloride Injection, USP or 5% Dextrose Injection, USP as recommended for infusion reflects the pH of the diluent used and ranges from 3.4 to 3.9.

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The following adverse reactions are discussed in more detail in other sections of the labeling:
  • Myelosuppression [see WARNINGS AND PRECAUTIONS]
  • Seizures [see WARNINGS AND PRECAUTIONS]
  • HVOD [see WARNINGS AND PRECAUTIONS]
  • Embryo-fetal Toxicity [see WARNINGS AND PRECAUTIONS]
  • Cardiac Tamponade [see WARNINGS AND PRECAUTIONS]
  • Bronchopulmonary Dysplasia [see WARNINGS AND PRECAUTIONS]
  • Cellular Dysplasia [see WARNINGS AND PRECAUTIONS]
Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Adverse reaction information is primarily derived from the clinical study (N=61) of BUSULFEX and the data obtained for high-dose oral busulfan conditioning in the setting of randomized, controlled trials identified through a literature review. In the BUSULFEX (busulfan) Injection allogeneic stem cell transplantation clinical trial, all patients were treated with BUSULFEX 0.8 mg per kg as a two-hour infusion every six hours for 16 doses over four days, combined with cyclophosphamide 60 mg per kg x2 days. Ninety-three percent (93%) of evaluable patients receiving this dose of BUSULFEX maintained an AUC less than 1,500 μM•min for dose 9, which has generally been considered the level that minimizes the risk of HVOD. Table 1 lists the non-hematologic adverse reactions events through BMT Day +28 at a rate greater than or equal to 20% in patients treated with BUSULFEX prior to allogeneic hematopoietic cell transplantation. Table 1: Summary of the Incidence (greater than or equal to 20%) of Non-Hematologic Adverse Reactions through BMT Day +28 in Patients who Received BUSULFEX Prior to Allogeneic Hematopoietic Progenitor Cell Transplantation
Non-Hematological Adverse Reactions1 Percent Incidence BODY AS A WHOLE   Fever 80   Headache 69   Asthenia 51   Chills 46   Pain 44   Edema General 28   Allergic Reaction 26   Chest Pain 26   Inflammation at Injection Site 25   Back Pain 23 CARDIOVASCULAR SYSTEM   Tachycardia 44   Hypertension 36   Thrombosis 33   Vasodilation 25 DIGESTIVE SYSTEM   Nausea 98   Stomatitis (Mucositis) 97   Vomiting 95   Anorexia 85   Diarrhea 84   Abdominal Pain 72   Dyspepsia 44   Constipation 38   Dry Mouth 26   Rectal Disorder 25   Abdominal Enlargement 23 METABOLIC AND NUTRITIONAL SYSTEM   Hypomagnesemia 77   Hyperglycemia 66   Hypokalemia 64   Hypocalcemia 49   Hyperbilirubinemia 49   Edema 36   SGPT Elevation 31   Creatinine Increased 21 NERVOUS SYSTEM   Insomnia 84   Anxiety 72   Dizziness 30   Depression 23 RESPIRATORY SYSTEM   Rhinitis 44   Lung Disorder 34   Cough 28   Epistaxis 25   Dyspnea 25 SKIN AND APPENDAGES   Rash 57   Pruritus 28 1 Includes all reported adverse reactions regardless of severity (toxicity grades 1-4)] Additional Adverse Reactions by Body System Hematologic: Prolonged prothrombin time Gastrointestinal: Esophagitis, ileus, hematemesis, pancreatitis, rectal discomfort Hepatic: Alkaline phosphatase increases, jaundice, hepatomegaly Graft-versus-host disease: Graft-versus-host disease. There were 3 deaths (5%) attributed to GVHD. Edema: Hypervolemia, or documented weight increase Infection: Infection, pneumonia (fatal in one patient and life-threatening in 3% of patients) Cardiovascular: Arrhythmia, atrial fibrillation, ventricular extrasystoles, third degree heart block, thrombosis (all episodes were associated with the central venous catheter), hypotension, flushing and hot flashes, cardiomegaly, ECG abnormality, left-sided heart failure, and pericardial effusion Pulmonary: Hyperventilation, alveolar hemorrhage (fatal in 3%), pharyngitis, hiccup, asthma, atelectasis, pleural effusion, hypoxia, hemoptysis, sinusitis, and interstitial fibrosis (fatal in a single case) Neurologic: Cerebral hemorrhage, coma, delirium, agitation, encephalopathy, confusion, hallucinations, lethargy, somnolence Renal: BUN increased, dysuria, oliguria, hematuria, hemorrhagic cystitis Skin: Alopecia, vesicular rash, maculopapular rash, vesiculo-bullous rash, exfoliative dermatitis, erythema nodosum, acne, skin discoloration Metabolic: Hypophosphatemia, hyponatremia Other Events: Injection site pain, myalgia, arthralgia, ear disorder Postmarketing Experience Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to establish a causal relationship to drug exposure. The following adverse reactions (reported as MedRA terms) have been identified during post-approval use of BUSULFEX (busulfan) Injection: Blood and Lymphatic System Disorders: febrile neutropenia Metabolism and Nutrition Disorders: tumor lysis syndrome Vascular Disorders: thrombotic microangiopathy (TMA) Infections and Infestations: severe bacterial, viral (e.g., cytomegalovirus viremia) and fungal infections; and sepsis. Oral Busulfan Literature Review A literature review identified four randomized controlled trials that evaluated a high-dose oral busulfan-containing conditioning regimen for allogeneic bone marrow transplantation in the setting of CML [see Clinical Studies]. The safety outcomes reported in those trials are summarized in Table 2 below for a mixed population of hematological malignancies (AML, CML, and ALL). Table 2: Summary of safety analyses from the randomized, controlled trials utilizing a high dose oral busulfancontaining conditioning regimen that were identified in a literature review.
Clift CML Chronic Phase TRM1 VOD2 GVHD3 Pulmonary Hemorrhagic Cystitis Seizure Death ≤ 100d =4.1% (3/73) No Report Acute≥Grade 2 =35% Chronic=41% (30/73) 1 death from Idiopathic Interstitial Pneumonitis And 1 death from Pulmonary Fibrosis No Report No Report Devergie CML Chronic Phase TRM VOD GVHD Pulmonary Hemorrhagic Cystitis Seizure 38% 7.7% (5/65) Deaths=4.6% (3/65) Acute≥Grade 2 =41% (24/59 at risk) Interstitial Pneumonitis= 16.9% (11/65) 10.8% (7/65) No report Ringden CML, AML, ALL TRM VOD GVHD Pulmonary Hemorrhagic Cystitis Seizure 28% 12% Acute≥Grade 2 GVHD=26% Chronic GVHD =45% Interstitial Pneumonitis =14% 24% 6% Blume CML, AML, ALL TRM VOD GVHD Pulmonary Hemorrhagic Cystitis Seizure No Report Deaths =4.9% Acute≥Grade 2 GVHD=22% (13/58 at risk) Chronic GVHD =31% (14/45 at risk) No Report No Report No Report 1 TRM = Transplantation Related Mortality
2 VOD = Veno-Occlusive Disease of the liver
3GVHD = Graft versus Host Disease Read the Busulfex (busulfan) Side Effects Center for a complete guide to possible side effectsLearn More »

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Initial Dosing Information
  • Administer BUSULFEX in combination with cyclophosphamide as a conditioning regimen prior to bone marrow or peripheral blood progenitor cell replacement. For patients weighing more than 12 kg, the recommended doses are:
    • BUSULFEX 0.8 mg per kg (ideal body weight or actual body weight, whichever is lower) intravenously via a central venous catheter as a two-hour infusion every six hours for four consecutive days for a total of 16 doses (Days -7, -6, -5 and -4).
    • Cyclophosphamide 60 mg per kg intravenously as a one-hour infusion on each of two days beginning no sooner than six hours following the 16th dose of BUSULFEX (Days -3 and -2).
    • Administer hematopoietic progenitor cells on Day 0.
  • Premedicate patients with anticonvulsants (e.g., benzodiazepines, phenytoin, valproic acid or levetiracetam) to prevent seizures reported with the use of high dose BUSULFEX. Administer anticonvulsants 12 hours prior to BUSULFEX to 24 hours after the last dose of BUSULFEX. [see WARNINGS AND PRECAUTIONS]
  • Administer antiemetics prior to the first dose of BUSULFEX and continue on a fixed schedule through BUSULFEX administration.
  • BUSULFEX clearance is best predicted when the BUSULFEX dose is administered based on adjusted ideal body weight. Dosing BUSULFEX based on actual body weight, ideal body weight or other factors can produce significant differences in BUSULFEX clearance among lean, normal and obese patients.
    • Calculate ideal body weight (IBW) as follows (height in cm, and weight in kg):
      Men: IBW (kg)=50+0.91x (height in cm -152)
      Women: IBW (kg)=45+0.91x (height in cm -152)
    • For obese or severely obese patients, base BUSULFEX dosing on adjusted ideal body weight (AIBW): AIBW= IBW +0.25x (actual weight -IBW).
Preparation And Administration Precautions DO NOT USE POLYCARBONATE SYRINGES OR POLYCARBONATE FILTER NEEDLES WITH BUSULFEX. Use an administration set with minimal residual hold-up volume (2-5 cc) for product administration. BUSULFEX is a cytotoxic drug. Follow applicable special handling and disposal procedures. Skin reactions may occur with accidental exposure. Use gloves when preparing BUSULFEX. If BUSULFEX or diluted BUSULFEX solution contacts the skin or mucosa, wash the skin or mucosa thoroughly with water. Visually inspect parenteral drug products for particulate matter and discoloration prior to administration whenever the solution and container permit. Do not use if particulate matter is seen in the BUSULFEX vial. Preparation For Intravenous Administration BUSULFEX must be diluted prior to intravenous infusion with either 0.9% Sodium Chloride Injection, USP (normal saline) or 5% Dextrose Injection, USP (D5W). The diluent quantity should be 10 times the volume of BUSULFEX, so that the final concentration of busulfan is approximately 0.5 mg per mL. Calculation of the dose for a 70 kg patient would be performed as follows: (70 kg patient) x (0.8 mg per kg) ÷ (6 mg per mL) =9.3 mL BUSULFEX (56 mg total dose). To prepare the final solution for infusion, add 9.3 mL of BUSULFEX to 93 mL of diluent (normal saline or D5W) as calculated below: (9.3 mL BUSULFEX) x (10) =93 mL of either diluent plus the 9.3 mL of BUSULFEX to yield a final concentration of busulfan of 0.54 mg per mL (9.3 mL x 6 mg per mL ÷ 102.3 mL =0.54 mg per mL). All transfer procedures require strict adherence to aseptic techniques, preferably employing a vertical laminar flow safety hood while wearing gloves and protective clothing. DO NOT put the BUSULFEX into an intravenous bag or large-volume syringe that does not contain normal saline or D5W. Always add the BUSULFEX to the diluent, not the diluent to the BUSULFEX. Mix thoroughly by inverting several times. Infusion pumps should be used to administer the diluted BUSULFEX solution. Set the flow rate of the pump to deliver the entire prescribed BUSULFEX dose over two hours. Prior to and following each infusion, flush the indwelling catheter line with approximately 5 mL of 0.9% Sodium Chloride Injection, USP or 5% Dextrose Injection, USP. DO NOT infuse concomitantly with another intravenous solution of unknown compatibility. WARNING: RAPID INFUSION OF BUSULFEX HAS NOT BEEN TESTED AND IS NOT RECOMMENDED.

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Itraconazole decreases busulfan clearance by up to 25%, and may produce an AUC greater than 1500 μM•min in some patients. Fluconazole (200 mg) has been used with BUSULFEX. Phenytoin increases the clearance of busulfan by 15% or more, possibly due to the induction of glutathione-S-transferase. Since the pharmacokinetics of BUSULFEX were studied in patients treated with phenytoin, the clearance of BUSULFEX at the recommended dose may be lower and exposure (AUC) higher in patients not treated with phenytoin. Because busulfan is eliminated from the body via conjugation with glutathione, use of acetaminophen prior to (less than 72 hours) or concurrent with BUSULFEX may result in reduced busulfan clearance based upon the known property of acetaminophen to decrease glutathione levels in the blood and tissues. Read the Busulfex Drug Interactions Center for a complete guide to possible interactions Learn More »

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BUSULFEX is indicated for use in combination with cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic progenitor cell transplantation for chronic myelogenous leukemia.

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BUSULFEX is contraindicated in patients with a history of hypersensitivity to any of its components. Last reviewed on RxList: 1/28/2015
This monograph has been modified to include the generic and brand name in many instances.

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There is no known antidote to BUSULFEX other than hematopoietic progenitor cell transplantation. In the absence of hematopoietic progenitor cell transplantation, the recommended dosage for BUSULFEX would constitute an overdose of busulfan. The principal toxic effect is profound bone marrow hypoplasia/aplasia and pancytopenia, but the central nervous system, liver, lungs, and gastrointestinal tract may be affected. Monitor hematologic status closely monitored and institute vigorous supportive measures as medically indicated. Survival after a single 140 mg dose of Myleran® Tablets in an 18 kg, 4-year old child has been reported. Inadvertent administration of a greater than normal dose of oral busulfan (2.1 mg per kg; total dose of 23.3 mg per kg) occurred in a 2-year old child prior to a scheduled bone marrow transplant without sequelae. An acute dose of 2.4 g was fatal in a 10-year old boy. There is one report that busulfan is dialyzable, thus dialysis should be considered in the case of overdose.

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Dosage Forms And Strengths BUSULFEX Injection is supplied as a clear, colorless, sterile, solution in 10 mL single use vial containing 60 mg of busulfan at a concentration of 6 mg per mL for intravenous use only. Storage And Handling How Supplied BUSULFEX is packaged as a sterile solution in 10 mL single-use clear glass vials each containing 60 mg of busulfan at a concentration of 6 mg per mL for intravenous use, NDC 59148-070-90. BUSULFEX is distributed as a unit carton of eight vials NDC 59148-070-91. Storage And Handling Unopened vials of BUSULFEX must be stored under refrigerated conditions between 2°C to 8°C (36°F to 46°F). BUSULFEX diluted in 0.9% Sodium Chloride Injection, USP or 5% Dextrose Injection, USP is stable at room temperature (25°C) for up to 8 hours but the infusion must be completed within that time. BUSULFEX diluted in 0.9% Sodium Chloride Injection, USP is stable at refrigerated conditions (2°C to 8°C) for up to 12 hours but the infusion must be completed within that time. BUSULFEX is a cytotoxic drug. Follow applicable special handling and disposal procedures.1 REFERENCES 1. OSHA Hazardous Drugs. OSHA. [Accessed on June 18, 2014 from http://www.osha.gov/SLTC/hazardousdrugs/index.html] Distributed and Marketed by: Otsuka America Pharmaceutical, Inc. Rockville, MD 20850. Manufactured by: DSM Pharmaceuticals, Inc. Greenville, NC 27834. Revision Date: January 2015. Otsuka Pharmaceutical Co., Ltd., Tokyo, 101-8535 Japan. Revised: 01/2015 Last reviewed on RxList: 1/28/2015
This monograph has been modified to include the generic and brand name in many instances.

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The following warnings pertain to different physiologic effects of BUSULFEX in the setting of allogeneic transplantation. Myelosuppression The most frequent serious consequence of treatment with BUSULFEX at the recommended dose and schedule is prolonged myelosuppression, occurring in all patients (100%). Severe granulocytopenia, thrombocytopenia, anemia, or any combination thereof may develop. Hematopoietic progenitor cell transplantation is required to prevent potentially fatal complications of the prolonged myelosuppression. Monitor complete blood counts, including white blood cell differentials, and quantitative platelet counts daily during treatment and until engraftment is demonstrated [see PATIENT INFORMATION]. Absolute neutrophil counts dropped below 0.5x109/L at a median of 4 days post-transplant in 100% of patients treated in the BUSULFEX clinical trial. The absolute neutrophil count recovered at a median of 13 days following allogeneic transplantation when prophylactic G-CSF was used in the majority of patients. Thrombocytopenia (less than 25,000/mm³ or requiring platelet transfusion) occurred at a median of 5-6 days in 98% of patients. Anemia (hemoglobin less than 8.0 g/dL) occurred in 69% of patients. Use antibiotic therapy and platelet and red blood cell support when medically indicated. Seizures Seizures have been reported in patients receiving high-dose oral busulfan at doses producing plasma drug levels similar to those achieved following the recommended dosage of BUSULFEX. Despite prophylactic therapy with phenytoin, one seizure (1/42 patients) was reported during an autologous transplantation clinical trial of BUSULFEX. This episode occurred during the cyclophosphamide portion of the conditioning regimen, 36 hours after the last BUSULFEX dose. Initiate phenytoin therapy or any other alternative anti-convulsant prophylactic therapy (e.g., benzodiazepines, valproic acid or levetiracetam) prior to BUSULFEX treatment [see DOSAGE AND ADMINISTRATION]. Use caution when administering the recommended dose of BUSULFEX to patients with a history of a seizure disorder or head trauma or who are receiving other potentially epileptogenic drugs [see PATIENT INFORMATION]. Hepatic Veno-Occlusive Disease (HVOD) Current literature suggests that high busulfan area under the plasma concentration verses time curve (AUC) values (greater than 1,500 μM•min) may be associated with an increased risk of developing HVOD. Patients who have received prior radiation therapy, greater than or equal to three cycles of chemotherapy, or a prior progenitor cell transplant may be at an increased risk of developing HVOD with the recommended BUSULFEX dose and regimen. Based on clinical examination and laboratory findings, HVOD was diagnosed in 8% (5/61) of patients treated with BUSULFEX in the setting of allogeneic transplantation, was fatal in 2/5 cases (40%), and yielded an overall mortality from HVOD in the entire study population of 2/61 (3%).Three of the five patients diagnosed with HVOD were retrospectively found to meet the Jones' criteria. The incidence of HVOD reported in the literature from the randomized, controlled trials was 7.7%12% [see Clinical Studies]. Monitor serum transaminases, alkaline phosphatase, and bilirubin daily through BMT Day +28 to detect hepatotoxicity, which may herald the onset of HVOD [see PATIENT INFORMATION]. Embryo-fetal Toxicity BUSULFEX can cause fetal harm when administered to a pregnant woman based on animal data. Busulfan was teratogenic in mice, rats, and rabbits. The solvent, DMA, may also cause fetal harm when administered to a pregnant woman based on findings in animals. Advise pregnant women of the potential risk to a fetus. Advise females and males of reproductive potential to use effective contraception during and after treatment with BUSULFEX [see Use in Specific Populations]. Cardiac Tamponade Cardiac tamponade has been reported in pediatric patients with thalassemia (8/400 or 2% in one series) who received high doses of oral busulfan and cyclophosphamide as the preparatory regimen for hematopoietic progenitor cell transplantation. Six of the eight children died and two were saved by rapid pericardiocentesis. Abdominal pain and vomiting preceded the tamponade in most patients. Monitor for signs and symptoms, promptly evaluate and treat if cardiac tamponade is suspected. Bronchopulmonary Dysplasia Bronchopulmonary dysplasia with pulmonary fibrosis is a rare but serious complication following chronic busulfan therapy. The average onset of symptoms is 4 years after therapy (range 4 months to 10 years). Cellular Dysplasia Busulfan may cause cellular dysplasia in many organs. Cytologic abnormalities characterized by giant, hyperchromatic nuclei have been reported in lymph nodes, pancreas, thyroid, adrenal glands, liver, lungs and bone marrow. This cytologic dysplasia may be severe enough to cause difficulty in the interpretation of exfoliative cytologic examinations of the lungs, bladder, breast and the uterine cervix. Nonclinical Toxicology Carcinogenesis, Mutagenesis, Impairment Of Fertility Busulfan is a mutagen and a clastogen. In in vitro tests it caused mutations in Salmonella typhimurium and Drosophila melanogaster. Chromosomal aberrations induced by busulfan have been reported in vivo (rats, mice, hamsters, and humans) and in vitro (rodent and human cells). The intravenous administration of busulfan (48 mg/kg given as biweekly doses of 12 mg/kg, or 30% of the total BUSULFEX dose on a mg/m² basis) has been shown to increase the incidence of thymic and ovarian tumors in mice. Busulfan depleted oocytes of female rats and induced sterility in male rats and hamsters. The solvent DMA may also impair fertility. A DMA daily dose of 0.45 g/kg/day given to rats for nine days (equivalent to 44% of the daily dose of DMA contained in the recommended dose of BUSULFEX on a mg/m² basis) significantly decreased spermatogenesis in rats. A single subcutaneous dose of 2.2 g/kg (27% of the total DMA dose contained in BUSULFEX on a mg/m² basis) four days after insemination terminated pregnancy in 100% of tested hamsters [see Use in Specific Populations]. Use In Specific Populations Pregnancy Risk Summary BUSULFEX can cause fetal harm when administered to a pregnant woman based on animal data. Busulfan was teratogenic in mice, rats, and rabbits following administration during organogenesis. The solvent, DMA, may also cause fetal harm when administered to a pregnant woman. In rats, DMA doses of approximately 40% of the daily dose of DMA in the BUSULFEX dose on a mg/m² basis given during organogenesis caused significant developmental anomalies [see Data]. There are no available human data informing the drug-associated risk. Advise pregnant women of the potential risk to a fetus. The background risk of major birth defects and miscarriage for the indicated populations are unknown. However, the background risk in the U.S. general population of major birth defects is 2-4% and of miscarriage is 15-20% of clinically recognized pregnancies. Animal Data Following administration during organogenesis in animals, busulfan caused malformations and anomalies, including significant alterations in the musculoskeletal system, body weight gain, and size. In pregnant rats, busulfan produced sterility in both male and female offspring due to the absence of germinal cells in the testes and ovaries. The solvent, DMA, administered to rats at doses of 400 mg/kg/day (about 40% of the daily dose of DMA in the BUSULFEX dose on a mg/m² basis) during organogenesis caused significant developmental anomalies. The most striking abnormalities included anasarca, cleft palate, vertebral anomalies, rib anomalies, and serious anomalies of the vessels of the heart. Lactation Risk Summary It is not known whether BUSULFEX is present in human milk. Because many drugs are excreted in human milk and because of the potential for tumorigenicity shown for busulfan in human and animal studies, discontinue breastfeeding during treatment with BUSULFEX. Females And Males Of Reproductive Potential Contraception Females BUSULFEX can cause fetal harm when administered to a pregnant woman [see Use In Specific Populations]. Advise females of reproductive potential to use effective contraception during and after treatment with BUSULFEX. Males BUSULFEX may damage spermatozoa and testicular tissue, resulting in possible genetic fetal abnormalities. Males with female sexual partners of reproductive potential should use effective contraception during and after treatment with BUSULFEX [see Nonclinical Toxicology]. Infertility Females Ovarian suppression and amenorrhea commonly occur in premenopausal women undergoing chronic, low-dose busulfan therapy for chronic myelogenous leukemia. Males Sterility, azoospermia, and testicular atrophy have been reported in male patients. Pediatric Use The effectiveness of BUSULFEX in the treatment of CML has not been specifically studied in pediatric patients. An open-label, uncontrolled study evaluated the pharmacokinetics of BUSULFEX in 24 pediatric patients receiving BUSULFEX as part of a conditioning regimen administered prior to hematopoietic progenitor cell transplantation for a variety of malignant hematologic (N=15) or non-malignant diseases (N=9). Patients ranged in age from 5 months to 16 years (median 3 years). BUSULFEX dosing was targeted to achieve an area under the plasma concentration curve (AUC) of 900-1350 μM•min with an initial dose of 0.8 mg per kg or 1.0 mg per kg (based on ABW) if the patient was greater than 4 or less than or equal to 4 years, respectively. The dose was adjusted based on plasma concentration after completion of dose 1. Patients received BUSULFEX doses every six hours as a two-hour infusion over four days for a total of 16 doses, followed by cyclophosphamide 50 mg per kg once daily for four days. After one rest day, hematopoietic progenitor cells were infused. All patients received phenytoin as seizure prophylaxis. The target AUC (900-1350±5% μM•min) for BUSULFEX was achieved at dose 1 in 71% (17/24) of patients. Steady state pharmacokinetic testing was performed at dose 9 and 13. BUSULFEX levels were within the target range for 21 of 23 evaluable patients. All 24 patients experienced neutropenia (absolute neutrophil count less than 0.5x109/L) and thrombocytopenia (platelet transfusions or platelet count less than 20,000/mm³). Seventy-nine percent (19/24) of patients experienced lymphopenia (absolute lymphocyte count less than 0.1x109). In 23 patients, the ANC recovered to greater than 0.5x109/L (median time to recovery = BMT day +13; range = BMT day +9 to +22). One patient who died on day +20 had not recovered to an ANC > 0.5x109/L. Four (17%) patients died during the study. Two patients died within 28 days of transplant; one with pneumonia and capillary leak syndrome, and the other with pneumonia and veno-occlusive disease. Two patients died prior to day 100; one due to progressive disease and one due to multi-organ failure. Adverse reactions were reported in all 24 patients during the study period (BMT day -10 through BMT day +28) or post-study surveillance period (day +29 through +100). These included vomiting (100%), nausea (83%), stomatitis (79%), HVOD (21%), graft-versus host disease (GVHD) (25%), and pneumonia (21%). Based on the results of this 24-patient clinical trial, a suggested dosing regimen of BUSULFEX in pediatric patients is shown in the following dosing nomogram: BUSULFEX Dosing Nomogram
Patient’s Actual Body Weight (ABW) BUSULFEX Dosage less than or equal to12 kgs 1.1 (mg per kg) greater than 12 kgs 0.8 (mg per kg) Simulations based on a pediatric population pharmacokinetic model indicate that approximately 60% of pediatric patients will achieve a target BUSULFEX exposure (AUC) between 900 to 1350 μM•min with the first dose of BUSULFEX using this dosing nomogram. Therapeutic drug monitoring and dose adjustment following the first dose of BUSULFEX is recommended. Dose Adjustment Based on Therapeutic Drug Monitoring Instructions for measuring the AUC of busulfan at dose 1 (see Blood Sample Collection for AUC Determination) and the formula for adjustment of subsequent doses to achieve the desired target AUC (1125 μM•min), are provided below. Adjusted dose (mg) = Actual Dose (mg) x Target AUC (μM•min)/Actual AUC (μM•min) For example, if a patient received a dose of 11 mg busulfan and if the corresponding AUC measured was 800 μM•min, for a target AUC of 1125 μM•min, the target mg dose would be: Mg dose =11 mg x 1125 μM•min /800 μM•min =15.5 mg Busulfex dose adjustment may be made using this formula and instructions below. Blood Sample Collection for AUC Determination Calculate the AUC (μM•min) based on blood samples collected at the following time points: For dose 1:2 hr (end of infusion), 4 hr and 6 hr (immediately prior to the next scheduled BUSULFEX administration). Actual sampling times should be recorded. For doses other than dose 1: Pre-infusion (baseline), 2 hr (end of infusion), 4 hr and 6 hr (immediately prior to the next scheduled BUSULFEX administration). AUC calculations based on fewer than the three specified samples may result in inaccurate AUC determinations. For each scheduled blood sample, collect one to three mL of blood into heparinized (Na or Li heparin) Vacutainer® tubes. The blood samples should be placed on wet ice immediately after collection and should be centrifuged (at 4°C) within one hour. The plasma, harvested into appropriate cryovial storage tubes, is to be frozen immediately at -20°C. All plasma samples are to be sent in a frozen state (i.e., on dry ice) to the assay laboratory for the determination of plasma busulfan concentrations. Calculation of AUC BUSULFEX AUC calculations may be made using the following instructions and appropriate standard pharmacokinetic formula: Dose 1 AUCinfinity Calculation: AUCinfinity = AUC0-6hr +AUCextrapolated, where AUC0-6hr is to be estimated using the linear trapezoidal rule and AUC extrapolated can be computed by taking the ratio of the busulfan concentration at Hour 6 and the terminal elimination rate constant, λz. The λz must be calculated from the terminal elimination phase of the busulfan concentration vs. time curve. A “0” pre-dose busulfan concentration should be assumed, and used in the calculation of AUC. If the AUC is assessed subsequent to Dose 1, steady-state AUCss (AUC0-6hr) is to be estimated from the trough, 2 hr, 4 hr and 6 hr concentrations using the linear trapezoidal rule. Instructions for Drug Administration and Blood Sample Collection for Therapeutic Drug Monitoring Use an administration set with minimal residual hold up (priming) volume (1-3 mL) for drug infusion to ensure accurate delivery of the entire prescribed dose and to ensure accurate collection of blood samples for therapeutic drug monitoring and dose adjustment. Prime the administration set tubing with drug solution to allow accurate documentation of the start time of BUSULFEX infusion. Collect the blood sample from a peripheral IV line to avoid contamination with infusing drug. If the blood sample is taken directly from the existing central venous catheter (CVC), DO NOT COLLECT THE BLOOD SAMPLE WHILE THE DRUG IS INFUSING to ensure that the end of infusion sample is not contaminated with any residual drug. At the end of infusion (2 hr), disconnect the administration tubing and flush the CVC line with 5 cc of normal saline prior to the collection of the end of infusion sample from the CVC port. Collect the blood samples from a different port than that used for the BUSULFEX infusion. When recording the BUSULFEX infusion stop time, do not include the time required to flush the indwelling catheter line. Discard the administration tubing at the end of the two-hour infusion [see DOSAGE AND ADMINISTRATION]. Geriatric Use Five of sixty-one patients treated in the BUSULFEX clinical trial were over the age of 55 (range 57-64). All achieved myeloablation and engraftment. Renal Impairment BUSULFEX has not been studied in patients with renal impairment. Hepatic Impairment BUSULFEX has not been administered to patients with hepatic insufficiency. Last reviewed on RxList: 1/28/2015
This monograph has been modified to include the generic and brand name in many instances.

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