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Busulfex

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Busulfex

Warnings
Precautions

WARNINGS

BUSULFEX should be administered under the supervision of a qualified physician experienced in hematopoietic stem cell transplantation. Appropriate management of complications arising from its administration is possible only when adequate diagnostic and treatment facilities are readily available.

The following warnings pertain to different physiologic effects of BUSULFEX in the setting of allogeneic transplantation.

Hematologic

The most frequent serious consequence of treatment with BUSULFEX at the recommended dose and schedule is profound myelosuppression, occurring in all patients. Severe granulocytopenia, thrombocytopenia, anemia, or any combination thereof may develop. Frequent complete blood counts, including white blood cell differentials, and quantitative platelet counts should be monitored during treatment and until recovery is achieved. 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 ( < 25,000/mm³ or requiring platelet transfusion) occurred at a median of 5-6 days in 98% of patients. Anemia (hemoglobin < 8.0 g/dL) occurred in 69% of patients. Antibiotic therapy and platelet and red blood cell support should be used when medically indicated.

Neurological

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. Anti-convulsant prophylactic therapy should be initiated prior to BUSULFEX treatment. Caution should be exercised 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.

Hepatic

Current literature suggests that high busulfan area under the plasma concentration verses time curve (AUC) values ( > 1,500 μM•min) may be associated with an increased risk of developing hepatic veno-occlusive disease (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, hepatic veno-occlusive disease 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 (see Clinical Studies) was 7.7%-12%.

Cardiac

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. No patients treated in the BUSULFEX (busulfan) Injection clinical trials experienced cardiac tamponade.

Pulmonary

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).

Carcinogenicity, Mutagenicity, 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. Four cases of acute leukemia occurred among 19 patients who became pancytopenic in a 243 patient study incorporating busulfan as adjuvant therapy following surgical resection of bronchogenic carcinoma. Clinical appearance of leukemia was observed 5-8 years following oral busulfan treatment. Busulfan is a presumed human carcinogen.

Ovarian suppression and amenorrhea commonly occur in premenopausal women undergoing chronic, low-dose busulfan therapy for chronic myelogenous leukemia. Busulfan depleted oocytes of female rats. Busulfan induced sterility in male rats and hamsters. Sterility, azoospermia and testicular atrophy have been reported in male patients.

The solvent DMA may also impair fertility. A DMA daily dose of 0.45 g/kg/d 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 sc 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.

Pregnancy

Busulfan may cause fetal harm when administered to a pregnant woman. Busulfan produced teratogenic changes in the offspring of mice, rats and rabbits when given during gestation. Malformations and anomalies included 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, may also cause fetal harm when administered to a pregnant woman. In rats, DMA doses of 400 mg/kg/d (about 40% of the daily dose of DMA in the BUSULFEX dose on a mg/m² basis) given 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. There are no adequate and well-controlled studies of either busulfan or DMA in pregnant women. If BUSULFEX is used during pregnancy, or if the patient becomes pregnant while receiving BUSULFEX, the patient should be apprised of the potential hazard to the fetus. Women of childbearing potential should be advised to avoid becoming pregnant.

PRECAUTIONS

Hematologic

At the recommended dosage of BUSULFEX (busulfan) Injection, profound myelosuppression is universal, and can manifest as neutropenia, thrombocytopenia, anemia, or a combination thereof. Patients should be monitored for signs of local or systemic infection or bleeding. Their hematologic status should be evaluated frequently.

Laboratory Tests

Patients receiving BUSULFEX should be monitored daily with a complete blood count, including differential count and quantitative platelet count, until engraftment has been demonstrated.

To detect hepatotoxicity, which may herald the onset of hepatic veno-occlusive disease, serum transaminases, alkaline phosphatase, and bilirubin should be evaluated daily through BMT Day +28.

Pregnancy

Pregnancy Category D. See WARNINGS.

Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for tumorgenicity shown for busulfan in human and animal studies, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Special Populations

Pediatric

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/kg or 1.0 mg/kg (based on ABW) if the patient was > 4 or _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/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 < 0.5 x 109/L) and thrombocytopenia (platelet transfusions or platelet count < 20,000/mm³). Seventy-nine percent (19/24) of patients experienced lymphopenia (absolute lymphocyte count < 0.1 x 109). In 23 patients, the ANC recovered to > 0.5 x 109/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 > 0.5 x 109/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 multiorgan failure.

Adverse events 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%), hepatic veno-occlusive disease (HVOD) (21%), graftversus 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 BUSULFEX Body Weight (ABW) Dosage
≤ 12 kgs 1.1 (mg/kg)
> 12 kgs 0.8 (mg/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 AUC infinity Calculation: AUC infinity = AUC 0-6hr + AUC extrapolated, 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 a nd 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

An administration set with minimal residual hold up (priming) volume (1-3 mL) should be used 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 Preparation for Intravenous Administration section for detailed instructions on drug preparation.

Geriatric

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.

Gender, Race

Adjusting BUSULFEX dosage based on gender or race has not been adequately studied.

Renal Insufficiency

BUSULFEX has not been studied in patients with renal impairment.

Hepatic Insufficiency

BUSULFEX has not been administered to patients with hepatic insufficiency.

Other

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.

Last reviewed on RxList: 8/5/2011
This monograph has been modified to include the generic and brand name in many instances.

Warnings
Precautions
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