BUSULFAN: 11,254 Adverse Event Reports & Safety Profile

Busulfan is a bifunctional alkylating agent known chemically as 1,4-butanediol, dimethanesulfonate.

Busulfan

Injection is intended for intravenous administration. It is supplied as a clear, colorless, sterile, solution in 10 mL single-dose vials. Each vial of busulfan injection contains 60 mg (6 mg/mL) of busulfan, the active ingredient, a white crystalline powder with a molecular formula of CH 3 SO 2 O(CH 2 ) 4 OSO 2 CH 3 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 busulfan injection 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. Str-1

AND USAGE Busulfan injection is indicated for use in combination with cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic progenitor cell transplantation for chronic myelogenous leukemia. Busulfan injection is an alkylating drug indicated for:

• Use in combination with cyclophosphamide as a conditioning regimen prior to allogeneic hematopoietic progenitor cell transplantation for chronic myelogenous leukemia (CML) ( 1 )

AND ADMINISTRATION Pre-medicate with anticonvulsants (e.g. benzodiazepines, phenytoin, valproic acid or levetiracetam) and antiemetic. ( 2.1 , 5.2 ) Dilute and administer as intravenous infusion. Do not administer as intravenous push or bolus. ( 2.1 , 2.3 ) Recommended adult dose: 0.8 mg per kg of ideal body weight or actual body weight, whichever is lower, administered intravenously via a central venous catheter as a two-hour infusion every six hours for four consecutive days for a total of 16 doses. ( 2.1 )

2.1 Initial Dosing Information 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: 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).

Cyclophosphamide

60 mg per kg intravenously as a one-hour infusion on each of two days beginning no sooner than six hours following the 16 th dose of busulfan injection (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 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) ]. Administer antiemetics prior to the first dose of busulfan injection and continue on a fixed schedule through busulfan injection administration. 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. 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 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 (2mL - 5mL) 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 or diluted busulfan 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. DO NOT put the busulfan injection into an intravenous bag or large-volume syringe that does not contain normal saline or D5W. Always add the busulfan injection to the diluent, not the diluent to the busulfan injection. Mix thoroughly by inverting several times. 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.

CONTRAINDICATIONS MYLERAN is contraindicated in patients in whom a definitive diagnosis of chronic myelogenous leukemia has not been firmly established. MYLERAN is contraindicated in patients who have previously suffered a hypersensitivity reaction to busulfan or any other component of the preparation.

REACTIONS The following adverse reactions are discussed in more detail in other sections of the labeling: Myelosuppression [see Warnings and Precautions ( 5.1 )] Seizures [see Warnings and Precautions ( 5.2 )]

Hepatic

Veno-Occlusive Disease (HVOD) [see Warnings and Precautions ( 5.3 )] Embryo-fetal Toxicity [see Warnings and Precautions ( 5.4 )]

Cardiac

Tamponade [see Warnings and Precautions ( 5.5 )]

Bronchopulmonary

Dysplasia [see Warnings and Precautions ( 5.6 )]

Cellular

Dysplasia [see Warnings and Precautions ( 5.7 )] Most common adverse reactions (incidence > 60%) were: myelosuppression, nausea, stomatitis, vomiting, anorexia, diarrhea, insomnia, fever, hypomagnesemia, abdominal pain, anxiety, headache, hyperglycemia and hypokalemia ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Sagent Pharmaceuticals, Inc. at 1-866-625-1618 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch .

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 Injection 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 Injection 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 x 2 days. Ninety-three percent (93%) of evaluable patients receiving this dose of Busulfan Injection 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 Injection 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 Busulfan Injection Prior to Allogeneic Hematopoietic Progenitor Cell Transplantation 1. Includes all reported adverse reactions regardless of severity (toxicity grades 1 to 4) Non-Hematological Adverse Reactions 1 Percent Incidence BODY AS A WHOLE Fever Headache Asthenia Chills Pain Edema General Allergic Reaction Chest Pain Inflammation at Injection Site Back Pain 80 69 51 46 44 28 26 26 25 23 CARDIOVASCULAR SYSTEM Tachycardia Hypertension Thrombosis Vasodilation 44 36 33 25 DIGESTIVE SYSTEM Nausea Stomatitis (Mucositis)

Vomiting Anorexia Diarrhea Abdominal Pain

Dyspepsia Constipation Dry Mouth Rectal Disorder Abdominal Enlargement 98 97 95 85 84 72 44 38 26 25 23 METABOLIC AND NUTRITIONAL SYSTEM Hypomagnesemia Hyperglycemia Hypokalemia Hypocalcemia Hyperbilirubinemia Edema SGPT Elevation Creatinine Increased 77 66 64 49 49 36 31 21 NERVOUS SYSTEM Insomnia Anxiety Dizziness Depression 84 72 30 23 RESPIRATORY SYSTEM Rhinitis Lung Disorder Cough Epistaxis Dyspnea 44 34 28 25 25 SKIN AND APPENDAGES Rash Pruritus 57 28 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 <span class="opacity-50 text-xs">[see Clinical Studies ( 14 )]</span> . 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 busulfan-containing conditioning regimen that were identified in a literature review. 1. TRM = Transplantation Related Mortality 2. VOD = Veno-Occlusive Disease of the liver 3. GVHD = Graft versus Host Disease Clift CML Chronic Phase TRM 1 VOD 2 GVHD 3 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

WARNINGS The most frequent, serious side effect of treatment with busulfan is the induction of bone marrow failure (which may or may not be anatomically hypoplastic) resulting in severe pancytopenia. The pancytopenia caused by busulfan may be more prolonged than that induced with other alkylating agents. It is generally felt that the usual cause of busulfan-induced pancytopenia is the failure to stop administration of the drug soon enough; individual idiosyncrasy to the drug does not seem to be an important factor. MYLERAN should be used with extreme caution and exceptional vigilance in patients whose bone marrow reserve may have been compromised by prior irradiation or chemotherapy, or whose marrow function is recovering from previous cytotoxic therapy. Although recovery from busulfan-induced pancytopenia may take from 1 month to 2 years, this complication is potentially reversible, and the patient should be vigorously supported through any period of severe pancytopenia. A rare, important complication of busulfan therapy is the development of bronchopulmonary dysplasia with pulmonary fibrosis. Symptoms have been reported to occur within 8 months to 10 years after initiation of therapy—the average duration of therapy being 4 years. The histologic findings associated with “busulfan lung” mimic those seen following pulmonary irradiation. Clinically, patients have reported the insidious onset of cough, dyspnea, and low-grade fever. In some cases, however, onset of symptoms may be acute. Pulmonary function studies have revealed diminished diffusion capacity and decreased pulmonary compliance. It is important to exclude more common conditions (such as opportunistic infections or leukemic infiltration of the lungs) with appropriate diagnostic techniques. If measures such as sputum cultures, virologic studies, and exfoliative cytology fail to establish an etiology for the pulmonary infiltrates, lung biopsy may be necessary to establish the diagnosis. Treatment of established busulfan-induced pulmonary fibrosis is unsatisfactory; in most cases the patients have died within 6 months after the diagnosis was established. There is no specific therapy for this complication. MYLERAN should be discontinued if this lung toxicity develops. The administration of corticosteroids has been suggested, but the results have not been impressive or uniformly successful. Busulfan may cause cellular dysplasia in many organs in addition to the lung. Cytologic abnormalities characterized by giant, hyperchromatic nuclei have been reported in lymph nodes, pancreas, thyroid, adrenal glands, liver, and bone marrow. This cytologic dysplasia may be severe enough to cause difficulty in interpretation of exfoliative cytologic examinations from the lung, bladder, breast, and the uterine cervix. In addition to the widespread epithelial dysplasia that has been observed during busulfan therapy, chromosome aberrations have been reported in cells from patients receiving busulfan. Busulfan is mutagenic in mice and, possibly, in humans. Malignant tumors and acute leukemias have been reported in patients who have received busulfan therapy, and this drug may be a human carcinogen.

The World Health

Organization has concluded that there is a causal relationship between busulfan exposure and the development of secondary malignancies. Four cases of acute leukemia occurred among 243 patients treated with busulfan as adjuvant chemotherapy following surgical resection of bronchogenic carcinoma.

All

4 cases were from a subgroup of 19 of these 243 patients who developed pancytopenia while taking busulfan 5 to 8 years before leukemia became clinically apparent. These findings suggest that busulfan is leukemogenic, although its mode of action is uncertain. Ovarian suppression and amenorrhea with menopausal symptoms commonly occur during busulfan therapy in premenopausal patients. Busulfan has been associated with ovarian failure including failure to achieve puberty in females. Busulfan interferes with spermatogenesis in experimental animals, and there have been clinical reports of sterility, azoospermia, and testicular atrophy in male patients. Hepatic veno-occlusive disease, which may be life threatening, has been reported in patients receiving busulfan, usually in combination with cyclophosphamide or other chemotherapeutic agents prior to bone marrow transplantation. Possible risk factors for the development of hepatic veno-occlusive disease include: total busulfan dose exceeding 16 mg/kg based on ideal body weight, and concurrent use of multiple alkylating agents (see CLINICAL PHARMACOLOGY and Drug Interactions). A clear cause-and-effect relationship with busulfan has not been demonstrated. Periodic measurement of serum transaminases, alkaline phosphatase, and bilirubin is indicated for early detection of hepatotoxicity. A reduced incidence of hepatic veno-occlusive disease and other regimen-related toxicities have been observed in patients treated with high-dose MYLERAN and cyclophosphamide when the first dose of cyclophosphamide has been delayed for >24 hours after the last dose of busulfan (see CLINICAL PHARMACOLOGY and Drug Interactions). Cardiac tamponade has been reported in a small number of patients with thalassemia (2% in one series) who received busulfan and cyclophosphamide as the preparatory regimen for bone marrow transplantation. In this series, the cardiac tamponade was often fatal. Abdominal pain and vomiting preceded the tamponade in most patients.

Pregnancy

Busulfan may cause fetal harm when administered to a pregnant woman. Although there have been a number of cases reported where apparently normal children have been born after busulfan treatment during pregnancy, one case has been cited where a malformed baby was delivered by a mother treated with busulfan. During the pregnancy that resulted in the malformed infant, the mother received x-ray therapy early in the first trimester, mercaptopurine until the third month, then busulfan until delivery. In pregnant rats, busulfan produces sterility in both male and female offspring due to the absence of germinal cells in testes and ovaries. Germinal cell aplasia or sterility in offspring of mothers receiving busulfan during pregnancy has not been reported in humans. There are no adequate and well-controlled studies in pregnant women. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus. Women of childbearing potential should be advised to avoid becoming pregnant.

PRECAUTIONS General The most consistent, dose-related toxicity is bone marrow suppression. This may be manifest by anemia, leukopenia, thrombocytopenia, or any combination of these. It is imperative that patients be instructed to report promptly the development of fever, sore throat, signs of local infection, bleeding from any site, or symptoms suggestive of anemia. Any one of these findings may indicate busulfan toxicity; however, they may also indicate transformation of the disease to an acute “blastic” form. Since busulfan may have a delayed effect, it is important to withdraw the medication temporarily at the first sign of an abnormally large or exceptionally rapid fall in any of the formed elements of the blood. Patients should never be allowed to take the drug without close medical supervision. Seizures have been reported in patients receiving busulfan. As with any potentially epileptogenic drug, caution should be exercised when administering busulfan to patients with a history of seizure disorder, head trauma, or receiving other potentially epileptogenic drugs. Some investigators have used prophylactic anticonvulsant therapy in this setting. Information for Patients Patients beginning therapy with busulfan should be informed of the importance of having periodic blood counts and to immediately report any unusual fever or bleeding. Aside from the major toxicity of myelosuppression, patients should be instructed to report any difficulty in breathing, persistent cough, or congestion. They should be told that diffuse pulmonary fibrosis is an infrequent, but serious and potentially life-threatening complication of long-term busulfan therapy. Patients should be alerted to report any signs of abrupt weakness, unusual fatigue, anorexia, weight loss, nausea and vomiting, and melanoderma that could be associated with a syndrome resembling adrenal insufficiency. Patients should never be allowed to take the drug without medical supervision and they should be informed that other encountered toxicities to busulfan include infertility, amenorrhea, skin hyperpigmentation, drug hypersensitivity, dryness of the mucous membranes, and rarely, cataract formation. Women of childbearing potential should be advised to avoid becoming pregnant. The increased risk of a second malignancy should be explained to the patient.

Laboratory

Tests It is recommended that evaluation of the hemoglobin or hematocrit, total white blood cell count and differential count, and quantitative platelet count be obtained weekly while the patient is on busulfan therapy. In cases where the cause of fluctuation in the formed elements of the peripheral blood is obscure, bone marrow examination may be useful for evaluation of marrow status. A decision to increase, decrease, continue, or discontinue a given dose of busulfan must be based not only on the absolute hematologic values, but also on the rapidity with which changes are occurring. The dosage of busulfan may need to be reduced if this agent is combined with other drugs whose primary toxicity is myelosuppression. Occasional patients may be unusually sensitive to busulfan administered at standard dosage and suffer neutropenia or thrombocytopenia after a relatively short exposure to the drug. Busulfan should not be used where facilities for complete blood counts, including quantitative platelet counts, are not available at weekly (or more frequent) intervals.

Drug Interactions

Busulfan may cause additive myelosuppression when used with other myelosuppressive drugs. In one study, 12 of approximately 330 patients receiving continuous busulfan and thioguanine therapy for treatment of chronic myelogenous leukemia were found to have portal hypertension and esophageal varices associated with abnormal liver function tests. Subsequent liver biopsies were performed in 4 of these patients, all of which showed evidence of nodular regenerative hyperplasia. Duration of combination therapy prior to the appearance of esophageal varices ranged from 6 to 45 months. With the present analysis of the data, no cases of hepatotoxicity have appeared in the busulfan-alone arm of the study. Long-term continuous therapy with thioguanine and busulfan should be used with caution. Busulfan-induced pulmonary toxicity may be additive to the effects produced by other cytotoxic agents. The concomitant systemic administration of itraconazole to patients receiving high-dose MYLERAN may result in reduced busulfan clearance (see CLINICAL PHARMACOLOGY). Patients should be monitored for signs of busulfan toxicity when itraconazole is used concomitantly with MYLERAN. Carcinogenesis, Mutagenesis, Impairment of Fertility See WARNINGS section.

The World Health

Organization has concluded that there is a causal relationship between busulfan exposure and the development of secondary malignancies.

Pregnancy Teratogenic

Effects: See WARNINGS section.

Nonteratogenic

Effects: There have been reports in the literature of small infants being born after the mothers received busulfan during pregnancy, in particular, during the third trimester. One case was reported where an infant had mild anemia and neutropenia at birth after busulfan was administered to the mother from the eighth week of pregnancy to term. Lactation It is not known whether this drug is excreted in human milk. Because of the potential for tumorigenicity shown for busulfan in animal and human 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.

Pediatric Use

See INDICATIONS AND USAGE and DOSAGE AND ADMINISTRATION sections.

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. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

INTERACTIONS Drugs that Decrease Busulfan Injection Clearance: Metronidazole, itraconazole, iron chelating agents, acetaminophen. ( 7.1 ) Drugs that Increase Busulfan Injection Clearance: Phenytoin. ( 7.2 )

7.1 Drugs that Decrease Busulfan Injection 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 Injection. 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 Injection 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 Injection 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 Injection 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 Injection were studied in patients treated with phenytoin, the clearance of Busulfan Injection at the recommended dose may be lower and exposure (AUC) higher in patients not treated with phenytoin.