2.1 Initial Dosing Information

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Administer busulfan injection 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:

o

Busulfan injection 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).

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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 busulfan injection (Days -3 and -2).

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Administer hematopoietic progenitor cells on Day 0.

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Premedicate patients with anticonvulsants (e.g., benzodiazepines, phenytoin, valproic acid or levetiracetam) to prevent seizures reported with the use of high dose busulfan injection. Administer anticonvulsants 12 hours prior to busulfan injection to 24 hours after the last dose of busulfan injection [see Warnings and Precautions (5.2)].

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Administer antiemetics prior to the first dose of busulfan injection and continue on a fixed schedule through busulfan injection administration.

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Busulfan injection clearance is best predicted when the busulfan injection dose is administered based on adjusted ideal body weight. Dosing busulfan injection based on actual body weight, ideal body weight or other factors can produce significant differences in busulfan injection clearance among lean, normal and obese patients.

o

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)

 

 

o

For obese or severely obese patients, base busulfan injection dosing on adjusted ideal body weight (AIBW):
 
AIBW = IBW +0.25x (actual weight -IBW)

2.2 Preparation and Administration Precautions

Busulfan injection is incompatible with polycarbonate. Do not use any infusion components (syringes, filter needles, intravenous tubing, etc.) containing polycarbonate with busulfan injection.

Use an administration set with minimal residual hold-up volume (2 mL to 5 mL) for product administration.

Busulfan injection is a cytotoxic drug. Follow applicable special handling and disposal procedures. Skin reactions may occur with accidental exposure. Use gloves when preparing busulfan injection. If busulfan injection or diluted busulfan injection 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 busulfan injection vial.

2.3 Preparation for Intravenous Administration

Busulfan injection 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 busulfan injection, 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 busulfan injection (56 mg total dose).

To prepare the final solution for infusion, add 9.3 mL of busulfan injection to 93 mL of diluent (normal saline or D5W) as calculated below:

(9.3 mL busulfan injection) x (10) = 93 mL of either diluent plus the 9.3 mL of busulfan injection 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.

Always add the busulfan injection to the diluent, not the diluent to the busulfan injection. Mix thoroughly by inverting several times. Discard unused portion.

Infusion pumps should be used to administer the diluted busulfan injection solution. Set the flow rate of the pump to deliver the entire prescribed busulfan injection 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 BUSULFAN INJECTION HAS NOT BEEN TESTED AND IS NOT RECOMMENDED.

5.1 Myelosuppression

The most frequent serious consequence of treatment with busulfan 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. Absolute neutrophil counts dropped below 0.5x109/L at a median of 4 days post-transplant in 100% of patients treated in the busulfan clinical trial. The absolute neutrophil count recovered at a median of 13 days following allogeneic transplantation when prophylactic filgrastim 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.

5.2 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 busulfan. Despite prophylactic therapy with phenytoin, one seizure (1/42 patients) was reported during an autologous transplantation clinical trial of busulfan. This episode occurred during the cyclophosphamide portion of the conditioning regimen, 36 hours after the last busulfan dose. Initiate phenytoin therapy or any other alternative anti-convulsant prophylactic therapy (e.g., benzodiazepines, valproic acid or levetiracetam) prior to busulfan treatment [see Dosage and Administration (2.1)]. Use caution when administering the recommended dose of busulfan to patients with a history of a seizure disorder or head trauma or who are receiving other potentially epileptogenic drugs.

5.3 Hepatic Veno-Occlusive Disease (HVOD)

Current literature suggests that high busulfan area under the plasma concentration versus 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 busulfan dose and regimen. Based on clinical examination and laboratory findings, HVOD was diagnosed in 8% (5/61) of patients treated with busulfan 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 (14)]. Monitor serum transaminases, alkaline phosphatase, and bilirubin daily through BMT Day +28 to detect hepatotoxicity, which may herald the onset of HVOD.

5.4 Embryo-fetal Toxicity

Busulfan 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 busulfan [see Use in Specific Populations (8.1), (8.3)].

5.5 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.

5.6 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).

5.7 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.

6.1 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 busulfan and the data obtained for high-dose oral busulfan conditioning in the setting of randomized, controlled trials identified through a literature review.

In the busulfan injection allogeneic stem cell transplantation clinical trial, all patients were treated with busulfan 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 busulfan 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 Bone Marrow Transplantation (BMT) Day +28 at a rate greater than or equal to 20% in patients treated with busulfan prior to allogeneic hematopoietic cell transplantation.

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

6.2 Postmarketing Experience

Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. The following adverse reactions have been identified during post-approval use of busulfan injection:

Blood and Lymphatic System Disorders: febrile neutropenia

Gastrointestinal Disorders: tooth hypoplasia

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.

6.3 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 (14)]. The safety outcomes reported in those trials are summarized in Table 2 below for a mixed population of hematological malignancies (AML, CML, and ALL).

7.1 Drugs that Decrease Busulfan Clearance

Itraconazole decreases busulfan clearance by up to 25%. Metronidazole decreases the clearance of busulfan to a greater extent than does itraconazole; metronidazole coadministration has been associated with increased busulfan toxicity. Fluconazole (200 mg) has been used with busulfan.

Decreased clearance of busulfan was observed with concomitant use with deferasirox. The mechanism of this interaction is not fully elucidated. Discontinue iron chelating agents well in advance of administration of busulfan to avoid increased exposure to busulfan.

Because busulfan is eliminated from the body via conjugation with glutathione, use of acetaminophen prior to (less than 72 hours) or concurrent with busulfan may result in reduced busulfan clearance based upon the known property of acetaminophen to decrease glutathione levels in the blood and tissues.

7.2 Drugs that Increase Busulfan Clearance

Phenytoin increases the clearance of busulfan by 15% or more, possibly due to the induction of glutathione-S-transferase. Since the pharmacokinetics of busulfan were studied in patients treated with phenytoin, the clearance of busulfan at the recommended dose may be lower and exposure (AUC) higher in patients not treated with phenytoin.

8.1 Pregnancy

8.2 Lactation

8.3 Females and Males of Reproductive Potential

8.4 Pediatric Use

The effectiveness of busulfan in the treatment of CML has not been specifically studied in pediatric patients. An open-label, uncontrolled study evaluated the pharmacokinetics of busulfan in 24 pediatric patients receiving busulfan 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). Busulfan 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 Actual Body Weight (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 busulfan 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 busulfan was achieved at dose 1 in 71% (17/24) of patients. Steady state pharmacokinetic testing was performed at dose 9 and 13. Busulfan levels were within the target range for 21 of 23 evaluable patients.

All 24 patients experienced neutropenia (absolute neutrophil count (ANC) 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 busulfan in pediatric patients is shown in the following dosing nomogram:

Simulations based on a pediatric population pharmacokinetic model indicate that approximately 60% of pediatric patients will achieve a target busulfan exposure (AUC) between 900 to 1350 µM•min with the first dose of busulfan using this dosing nomogram. Therapeutic drug monitoring and dose adjustment following the first dose of busulfan 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

Busulfan 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 busulfan 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 busulfan 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

Busulfan 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 to 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 busulfan 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 mL 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 busulfan infusion. When recording the busulfan 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 (2.3)].

8.5 Geriatric Use

Clinical studies of busulfan did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects.

12.1 Mechanism of Action

Busulfan is a bifunctional alkylating agent in which two labile methanesulfonate groups are attached to opposite ends of a four-carbon alkyl chain. In aqueous media, busulfan hydrolyzes to release the methanesulfonate groups. This produces reactive carbonium ions that can alkylate DNA. DNA damage is thought to be responsible for much of the cytotoxicity of busulfan.

12.3 Pharmacokinetics

The pharmacokinetics of busulfan were studied in 59 patients participating in a prospective trial of a busulfan-cyclophosphamide preparatory regimen prior to allogeneic hematopoietic progenitor stem cell transplantation. Patients received 0.8 mg/kg busulfan every six hours, for a total of 16 doses over four days. Fifty-five of fifty-nine patients (93%) administered busulfan maintained AUC values below the target value (less than 1500 μM•min).

Busulfan pharmacokinetics showed consistency between dose 9 and dose 13 as demonstrated by reproducibility of steady state Cmax and a low coefficient of variation for this parameter.

Distribution: Busulfan achieves concentrations in the cerebrospinal fluid approximately equal to those in plasma. Busulfan primarily binds to albumin (Mean ± standard deviation = 32.4 ± 2.2%).

Metabolism: Busulfan is predominantly metabolized by conjugation with glutathione, both spontaneously and by glutathione S-transferase (GST) catalysis. This conjugate undergoes extensive oxidative metabolism in the liver.

Excretion: Following administration of 14C-labeled busulfan to humans, approximately 30% of the radioactivity was excreted into the urine over 48 hours; negligible amounts were recovered in feces.

Specific Populations

Pediatric Patients: In a pharmacokinetic study of busulfan injection in 24 pediatric patients, the population pharmacokinetic (PPK) estimates of busulfan injection for clearance (CL) and volume of distribution (V) were determined. For actual body weight, PPK estimates of CL and V were 4.04 L/hr per 20 kg (3.37 mL per min per kg; interpatient variability 23%); and 12.8 L per 20 kg (0.64 L per kg; interpatient variability 11%).

13.1 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 busulfan 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 busulfan 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 busulfan on a mg/m2 basis) four days after insemination terminated pregnancy in 100% of tested hamsters [see Use in Specific Populations (8.3)].

16.1 How Supplied

Busulfan Injection is packaged as a sterile solution in 10 mL single-dose clear glass vials, NDC 67457-893-00.

Busulfan Injection is distributed as a unit carton of eight vials, NDC 67457-893-08.

16.2 Storage and Handling

Unopened vials of busulfan injection must be stored under refrigerated conditions between 2°C to 8°C (36°F to 46°F). Discard unused portion.

Busulfan injection 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.

Busulfan injection 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.

Busulfan injection is a cytotoxic drug. Follow applicable special handling and disposal procedures.1