PRODUCT MONOGRAPH NAME OF DRUG (r)

BUSULFEX

(Busulfan) Injection 6 mg/mL BUSULFEX (BUSULFAN) INJECTION IS A POTENT CYTOTOXIC DRUG THAT RESULTS IN PROFOUND MYELOSUPPRESSION AT THE RECOMMENDED DOSAGE. IT SHOULD BE ADMINISTERED UNDER THE SUPERVISION OF A QUALIFIED PHYSICIAN WHO IS EXPERIENCED IN THE USE OF CANCER CHEMOTHERAPEUTIC AGENTS AND IN THE MANAGEMENT OF PATIENTS WITH SEVERE PANCYTOPENIA. APPROPRIATE MANAGEMENT OF THERAPY AND COMPLICATIONS IS ONLY POSSIBLE WHEN ADEQUATE DIAGNOSTIC AND TREATMENT FACILITIES ARE READILY AVAILABLE.

ACTIONS AND CLINICAL PHARMACOLOGY

Busulfan is a potent cytotoxic agent and a bifunctional alkylating agent. In aqueous media, release of the methanesulfonate group produces carbonium ions, which can alkylate DNA, thought to be an important biological mechanism for its cytotoxic effect. Current literature suggests that high AUC values (>1,500 mMol-min) may be associated with an increased risk of developing hepatic veno-occlusive disease and/or seizures. Mean Cmax, AUC, T1/2 and plasma clearance are provided below for oral busulfan and iv BUSULFEX (busulfan) (See PHARMACOLOGY).

Intravenous BUSULFEX. had a more consistent pharmacokinetic profile than oral busulfan among patients. Busulfan achieves concentrations in the cerebrospinal fluid approximately equal to those in plasma. Irreversible binding to plasma elements, primarily albumin, has been estimated to be 32.4 + 2.2%, which is consistent with the reactive electrophilic properties of this alkylator. Busulfan is predominately metabolized through conjugation with glutathione, both spontaneously and through glutathione S-transferase (GST).

CONTRAINDICATIONS

BUSULFEX (busulfan) Injection is contraindicated in patients who are sensitive, allergic or intolerant of the drug or its vehicle.

WARNINGS

BUSULFEX (busulfan) Injection is a potent cytotoxic drug that results in profound myelosuppression at the recommended dosage. It should be administered under the supervision of a qualified physician who is experienced in the use of cancer chemotherapeutic agents and in the management of patients with severe pancytopenia. Appropriate management of therapy and complications is only possible when adequate diagnostic and treatment facilities are readily available. 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 <0.5 x 109/L at a median of 4 days post transplant occurred in 100% of patients and recovered at median day 10 following transplant (median neutropenic period of 6 days). Prophylactic or empiric use of anti-infectives (bacterial, fungal, viral) should be considered for prevention and management of infections during the neutropenic period. Thrombocytopenia (<25,000/mm3 or requiring platelet transfusion) at a median of 5-6 days occurred in 98% of patients. Anemia (hemoglobin <8.0 g/dL) occurred in 69% of patients. Platelet and red blood cell support should be employed as medically indicated. Busulfan may be a human carcinogen. Several cases of leukemia have occurred 5-8 years following oral busulfan treatment. Ovarian suppression and amenorrhea commonly occur in premenopausal women undergoing chronic, low-dose busulfan therapy for chronic myelogenous leukemia. Sterility, azoospermia and testicular atrophy have been reported in male patients. Bronchopulmonary dysplasia with pulmonary fibrosis is a rare complication following chronic busulfan therapy. The average onset of symptoms is after 4 years of therapy (range 4 months to 10 years).

Pregnancy:

Busulfan can cause fetal harm when administered to a pregnant woman. There are no adequate and well-controlled studies in pregnant women. If BUSULFEX 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.

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 tumorigenicity 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.

Hepatic Insufficiency:

BUSULFEX has not been administered to patients with hepatic insufficiency. However, patients who have received prior radiation therapy, greater than three cycles of chemotherapy, or a prior progenitor cell transplant may be at an increased risk of

developing hepatic veno-occlusive disease with the recommended BUSULFEX dose and regimen.

PRECAUTIONS

General:

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

Caution should be exercised when administering the recommended dose of BUSULFEX to patients with a history of seizure disorder, head trauma, or receiving other potentially epileptogenic drugs. It is recommended that phenytoin be administered prophylactically to such patients. Seizures have been reported with high dose oral busulfan treatment.

Information for Patients:

The increased risk of a second malignancy should be explained to the patient.

Monitoring:

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 transplant day 28. Drug Interactions: There are no known or manifest interactions with antifungal agents (fluconazole), known glutathione transferase (GST) inhibitors (itraconazole) and 5-HT3 antiemetics such as odansetron (Zofran(r)) and granisetron (Kytril(r)). It has been reported that phenytoin increases the clearance of busulfan by 10% or more, possibly due to the induction of GST. Since virtually all patients are empirically treated with anticonvulsants (phenytoin, clonazepam), the dose of BUSULFEX should be adjusted to account for enhanced clearance (See DOSAGE AND ADMINISTRATION). Busulfan is eliminated from the body via conjugation with glutathione. Since acetaminophen may decrease glutathione levels in blood and tissues, concurrent or prior use (<72 hours) may result in modified busulfan clearance.

Pediatric:

A BUSULFEX conditioning regimen above has been used in pediatric patients as

young as 4 years of age.

Older Patients:

Patients older than 50 years of age (n=23) have been successfully treated with BUSULFEX as measured by myeloablation and engraftment and which was well tolerated in these patients.

Gender/Race:

Dosing with BUSULFEX does not need adjustment for gender or race.

Renal Insufficiency:

Studies in renally impaired patients have not been conducted; however, busulfan is not significantly metabolized by the kidney or excreted in the urine.

SYMPTOMS AND TREATMENT OF OVERDOSAGE

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. There is no known antidote to busulfan overdosage, other than hematopoietic progenitor cell transplantation. The hematologic status should be closely monitored and vigorous supportive measures instituted as medically indicated. In the absence of hematopoietic progenitor cell transplantation, the recommended dosage for BUSULFEX (busulfan) would constitute an overdose of busulfan. Survival after a single 140-mg dose of Myleran(r) 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/kg; total dose of 23.3 mg/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 has been one report that busulfan is dialyzable, thus dialysis should be considered in the case of an overdose. Busulfan is metabolized through conjugation with glutathione, thus administration of glutathione may be considered.

DOSAGE AND ADMINISTRATION

BUSULFEX (busulfan) should be administered intravenously via a central venous catheter as a two-hour infusion every 6 hours x 4 consecutive days for a total of 16 doses. All patients should be premedicated with phenytoin to prevent seizures, as busulfan is known to cross the blood brain barrier. Antiemetics of the 5-HT3 class should be administered prior to the first dose of BUSULFEX and continued on a fixed schedule through administration of BUSULFEX or considered through completion of the preparative regimen. The usual adult dose of BUSULFEX in combination with cyclophosphamide as a preparative regimen prior to bone marrow or peripheral blood progenitor cell replacement support is 0.8 mg/kg of ideal body weight or actual body weight, whichever is lower. For obese or severely obese patients, dosing based on adjusted ideal body weight could be considered. Ideal body weight (IBW) should be calculated as follows (height in cm, and weight in kg): IBW (kg; men) = 50 + 0.91 x (height -152); IBW (kg, women) = 45 + 0.91 x (height -152). Adjusted ideal body weight (AIBW) should be calculated as follows: AIBW = IBW + 0.25 x (actual weight - IBW). Cyclophosphamide in combination with BUSULFEX was given on each of two days as a one-hour infusion at 60 mg/kg beginning on BMT day -3, six hours following the 16th dose of BUSULFEX. Note: Instructions for reconstitution and special precautions can be found under the section PHARMACEUTICAL INFORMATION, subsection RECONSTITUTED SOLUTIONS.

Drug Substance:

PHARMACEUTICAL INFORMATION

Common Name:

Busulfan

Chemical Names: 1,4-butanediol-dimethanesulfonate Chemical Structure: Molecular Formula: C6H14O6S2

Molecular Weight:

246.31

Description:

Busulfan is a white crystalline solid that is only very slightly soluble in water, sparingly soluble in acetone and slightly soluble in ethanol. The pH profile is not applicable since the drug product is only very slightly soluble in water.

Melting Range:

115 - 118 oC

Composition:

Active Ingredient:

Each 10 mL ampule or vial contains 60 mg busulfan, USP.

Non-medicinal Ingredients:

Each 10 mL ampule or vial also contains the ingredients

dimethylacetamide and polyethylene glycol 400, NF, in quantities of 3.333 mL and 6.667 mL, respectively.

Stability And Storage Recommendations:

Unopened ampules or vials of BUSULFEX Injection must be stored under refrigerated conditions between 2 - 8 oC (36 - 46 oF). BUSULFEX diluted in 0.9% Sodium Chloride Injection, USP or 5% Dextrose Injection, USP is stable at room temperature (25 oC) 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 (2-8 degC) for up to 12 hours but the infusion must be completed within that time.

FREEZING OF DILUTED PREPARATIONS OF BUSULFEX IS NOT RECOMMENDED.

Reconstituted Solutions:

Preparation for Intravenous Administration:

As with all parenteral drug products, intravenous admixtures should be inspected visually for clarity, particulate matter, precipitate, discoloration and leakage prior to administration, whenever solution and container permit. Discard unused portion. BUSULFEX must be diluted prior to use 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 Injection, so that the final concentration is approximately 0.5 mg/mL. By way of example, for a 70 kg patient, the amount of drug to be administered would be calculated as follows:

(70 kg patient) x (0.8 mg/kg) / (6 mg/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/mL (9.3 mL x 6 mg/mL / 102.3 mL = 0.54 mg/mL). All transfer procedures require strict adherence to aseptic techniques, preferably employing a vertical laminar flow safety hood while wearing gloves and protective clothing. For ampules, using sterile transfer techniques, break off the top of the ampule. Using a syringe fitted with a needle and the 5 micron nylon filter provided with each BUSULFEX ampule, remove the calculated volume of BUSULFEX Injection from the ampule. Remove the needle and filter, replace with a new needle and dispense the content of the syringe into an intravenous bag (or syringe) that already contains the calculated amount of either normal saline or D5W, making sure that the drug flows into and through the solution. For vials, using a syringe fitted with a needle, remove the calculated volume of BUSULFEX Injection from the vial and dispense the contents of the syringe into an intravenous bag (or syringe) that already contains the calculated amount of either normal saline or D5W, making sure that the drug flows into and through the solution. DO NOT put the BUSULFEX Injection into an intravenous bag 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 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: BUSULFEX SHOULD NOT BE GIVEN BY RAPID INTRAVENOUS INJECTION OR BOLUS.

Parenteral Products:

Intravenous Injection

1. 0.9% Sodium Chloride Injection USP

Ampule/Vial Size (mL)

Volume of Diluent to be Added (mL) (for a 70 kg patient)

Approximate Available Volume (for a 70 kg patient)

Nominal Concentration per mL

10 93 102 0.5 mg

5% Dextrose Injection, USP

Ampule/Vial Size Volume of Diluent to be Approximate Available Nominal Concentration per

(mL) Added (mL) (for a 70 kg patient)

Volume (for a 70 kg mL patient)

10 93 102 0.5 mg

By way of example, for a 70 kg patient, the amount of drug to be administered would be calculated as follows: (70 kg patient) x (0.8 mg/kg) / (6 mg/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/mL (9.3 mL x 6 mg/mL / 102.3 mL = 0.54 mg/mL).

Special Instructions:

Preparation and Administration Precautions:

As with other cytotoxic compounds, caution should be exercised in handling and preparing the solution of BUSULFEX. Skin reactions may occur with accidental exposure. The use of gloves is recommended. If BUSULFEX or diluted BUSULFEX solution contacts the skin or mucosa, wash the skin or mucosa thoroughly with water.

DO NOT USE POLYCARBONATE SYRINGES OR POLYCARBONATE FILTER NEEDLES WITH BUSULFEX. USE OF FILTERS OTHER THAN THE SPECIFIC TYPE INCLUDED IN THE PACKAGE WITH EACH AMPULE IS NOT RECOMMENDED. Procedures for proper handling and disposal of anticancer drugs should be considered. Several guidelines on this subject have been published. There is no general agreement that all of the procedures recommended in the guidelines are necessary or appropriate.

AVAILABILITY OF DOSAGE FORMS

BUSULFEX (busulfan) Injection is supplied as a sterile solution in 10 mL single-use clear glass ampules or vials each containing 60 mg of busulfan at a concentration of 6 mg/mL for intravenous use. BUSULFEX is provided in packages of eight ampules including eight compatible 25 mm 5.0 um Nylon Membrane syringe filters or in packages of eight vials (the membrane filter is not required for vials).

PHARMACOLOGY

Busulfan is an alkylating agent producing DNA cross-linking and chromosomal damage that can be lethal to rapidly dividing cells. At the low end of the active dose range, busulfan causes a selective depression of granulocytopoiesis. Increasing doses lead to progressive general myelotoxicity culminating in marrow ablation due to cell death. In several animal species and man, oral doses of busulfan result in a prolonged depression in hemopoietic progenitor cells. The drug reduces the ability of the cell to differentiate progeny and produces a delayed, but prolonged, hematological depression. High doses cause significant DNA and genetic damage and are myeloablative, killing the marrow cells. The selectivity of busulfan for marrow cells has several explanations. One theory is based on the susceptibility of relatively undifferentiated stem cells during the G-phase of the cell mitotic cycle to alkylation by busulfan. Busulfan treatment during the G-phase prevents further differentiation and progression of the cell through other stages. Microscopic examination of various stem cell populations indicates arrested cell division with polyploidy and cell death. The more differentiated types of progenitor cells show relatively less genetic damage from busulfan exposure, which has been attributed to increased exposure in the S-phase of the cell cycle. In this phase, active DNA repair reduces the damage produced by busulfan. There were few general acute pharmacological effects of busulfan reported in the literature. Higher doses of busulfan in the myelotoxic range produce emesis, and myoclonic seizures in animals and man, but treatment with anticonvulsant drugs can prevent the seizures, and Droperidol and other antiemetics have been useful in treating the emesis. Flushing has been reported in monkeys after IV administration. Most of the side effects reported for busulfan occurred more than three to four days following high acute doses or chronic treatment. These effects have been attributed to the genetic damage caused by busulfan. The relative selectivity of the drug for the more undifferentiated progenitor, or stem, cells has been used to explain certain actions of busulfan on other organ systems, especially gonadal changes leading to sterility and lenticular distortion and cataracts in the eye. Genetic damage to alveolar cells may explain the pulmonary fibrosis that can occur in the lung following chronic treatment with busulfan. In addition, mechanical damage from busulfan crystals in the liver may be the basis of veno-occlusive disease. There is also a low incidence of sudden cardiac tamponade related to haemochromatosis that occurs in man; this has not been reported in animals. There were no reports found in the literature of acute cardiovascular pharmacology. The major longer-term effects of busulfan appear to be mediated by genetic damage, especially in stem cell compartments. Thus, with the exception of neurotoxicity and mechanical damage to the liver, busulfan exhibits relatively benign pharmacological effects over most of its active dose range. Pharmacokinetic studies have demonstrated that busulfan distributes from the blood to various organs within minutes, but is primarily found in the liver, lung and brain. Despite its rapid tissue distribution, low, but constant levels remain in the plasma for an extended period of time. Following intraperitoneal (IP) or IV administration, three main urinary metabolites have been identified: 3-hydroxysulfolane, tetrahydrothiophene 1-oxide and sulfolane. The sulfonium ion of glutathione, or g-glutamyl-b-(S-tetrahydrothiophenium) alanyl-glycine, was also hypothesized as a urinary metabolite, but because of its instability, it has only been measured indirectly. Unreacted busulfan is excreted in small amounts. Finally, excretion occurs primarily through the urine followed by exhaled CO2 and the feces. The pharmacokinetics of BUSULFEX (busulfan) were studied in 27 patients participating in two prospective trials of a busulfan/cyclophosphamide preparatory regimen prior to hematopoietic progenitor cell transplantation. Patients received busulfan every six hours for a total of 16 doses over four days. In twelve patients the initial dose was administered orally at 1.0 mg/kg, followed six hours later by the first of 15 two-hour intravenous infusions of 0.8 mg/kg. Nine of twelve patients contributed fully analyzable pharmacokinetic data for both oral and intravenous modes of administration (Table 4). In comparing the action of BUSULFEX to oral busulfan in the same patient group, 92% of patients administered BUSULFEX maintained AUC values below the target value (<1500 uMol-min) while only 67% of evaluable patients administered oral busulfan had an AUC below this target level. Of the three patients who could not be analyzed, two were due to delayed absorption of the oral formulation and one was due to delayed plasma collection.

When maximum concentration, AUC, elimination half-life, and plasma clearance are compared for intravenous and oral routes of administration, intravenous busulfan had a more consistent pharmacokinetic profile among patients. When the coefficients of variation for all pharmacokinetic parameters are compared, those for BUSULFEX ranged from 9.8%-17% and those for the oral busulfan from 17-46%. BUSULFEX demonstrated consistency between dose 1 and dose 9, and between dose 9 and dose 13 as demonstrated by predictability of Tmax, reproducibility of steady state Cmax and AUC, and low coefficients of variation of these parameters. Because BUSULFEX allows predictable drug exposure, the pharmacokinetic profile of the first intravenous BUSULFEX dose predicts with high precision the steady state AUC values of subsequent doses. The predictability of BUSULFEX allows the physician to target the optimal systemic exposure to achieve the appropriate balance between therapeutic effectiveness and dose-limiting toxicity effects. If the patient's body size is normalized as body surface area (m2) or adjusted ideal body weight, differences in clearance are not significant among body weight groups (underweight, normal, obese, and severely obese). Overall, 90% of patients delivered BUSULFEX, maintained AUC's lower than the targeted level of 1500 uMol-min. When BUSULFEX is delivered, the resulting AUC can be predicted with high precision. BUSULFEX systemic exposure is immediate and complete due to intravenous administration. Studies of distribution, metabolism, and elimination of BUSULFEX have not been done; however, the literature on oral busulfan is relevant. Additionally, for modulating effects on pharmacodynamic parameters. (See PRECAUTIONS - Drug Interactions.) Busulfan achieves concentrations in the cerebrospinal fluid approximately equal to those in plasma. Irreversible binding to plasma elements, primarily albumin, has been estimated to be 32.4 + 2.2%, which is consistent with the reactive electrophilic properties of this alkylator. Busulfan is eliminated through conjugation with glutathione, both spontaneously and through glutathione S-transferase (GST). In humans, approximately 30% of 14C-labelled busulfan was excreted into the urine over 48 hours; negligible amounts were recovered in feces. The lack of complete urine label recovery may be due to the production of long-lived metabolites or due to nonspecific alkylation of macromolecules.

CLINICAL STUDIES

Documentation of the safety and efficacy of busulfan in combination with cyclophosphamide or other drugs as a conditioning regimen prior to hematopoietic progenitor cell reconstitution derives from two sources:

1. analysis of two prospective clinical trials of BUSULFEX (busulfan) in 103 patients diagnosed with various hematologic malignancies,

2. a review of the world literature addressing the clinical use of high-dose oral busulfan in the transplant setting since 1964. Forty-three publications (2,197 patients) were selected for review based on availability of engraftment rate and days to engraftment as well as sufficient patients (> 23) to provide confidence in the engraftment rate reported. In addition, information on disease response, relapse, durations of disease-free and overall survival, adverse events, and acute mortality (death within the first month following transplant) was included.

Clinical Trials:

Two prospective, single-arm, open-label, uncontrolled trials of 103 patients administered BUSULFEX differed only in that hematopoietic progenitor cells were of autologous origin in one trial and allogeneic origin in the other and that allogeneic transplant patients received graft versus host disease prophylaxis. Diseases included were acute leukemia past first remission, in first or subsequent relapse, in first remission (high-risk), or induction failures; chronic myelogenous leukemia in chronic phase, accelerated phase or blast crisis; primary refractory or resistant relapsed Hodgkin's disease or non-Hodgkin's lymphoma; and myelodysplastic syndrome. Patients received BUSULFEX doses of 0.8 mg/kg every 6 hours as a two-hour infusion for 4 days, followed by 2 daily doses of cyclophosphamide at 60 mg/kg once per day for two days (BuCy2 regimen). After one rest day, hematopoietic progenitor cells were infused. The primary efficacy parameters in these studies were myeloablation (defined as one or more of the following: absolute neutrophil count [ANC] less than 0.5 x 109/L, absolute lymphocyte count [ALC] less than 0.1 x 109/L, thrombocytopenia defined as a platelet count less than 20,000/mm3 or a platelet transfusion requirement), engraftment (ANC > 0.5 x 109/L), relapse, and survival. In both studies, all patients received and retained their prescribed 16/16 dose regimen of BUSULFEX. No patients were discontinued from treatment due to adverse events related to BUSULFEX. All patients experienced profound myelosuppression. The studies are described individually in Table 5 and Table 6..

Table 5:Summary of Autologous Study and Allogenic Study with BUSULFEX

*Defined as having at least one of the following: prior radiation, > 3 prior chemotherapeutic regimens, or prior hematopoietic

progenitor cell transplant.

Days expressed as BMT = day 0

Discussion of Literature:

There were 2,197 patients treated with high-dose oral busulfan in the 43 publications analyzed. The availability of endpoint information was highly variable among publications. These trials included high-dose oral busulfan combined with other chemotherapeutic agents, including cyclophosphamide in 87% of patients and a smaller percentage with irradiation. Adult and pediatric patients, as well as multiple disease types were included in many studies. Data obtained are as follows: 72% of the transplants were allogeneic and 28% were autologous. Acute leukemias were the conditions most frequently treated (49%), followed by chronic myeloid leukemia (24%), lymphoma (7%), multiple myeloma (7%), myelodysplastic syndrome (5%), breast cancer (4%), ovarian cancer (1%). The range of median days of duration of neutropenia in patients treated with a high-dose oral busulfan conditioning regimen was 7-11 days for autologous and allogeneic transplant patients combined from the literature. In a single dose escalation study of busulfan with total doses from 8-16 mg/kg, white blood cell nadirs occurred 2-8 days after transplant and granulocyte (neutrophil) levels recovered to 0.5 x 109/L in a mean of 21 days (range 14-26 days). Among 34 studies reporting white blood cell recovery to 0.5 x 109/L, the average of the medians was 16.5 days (range of medians 8-42 days). Among the 32 studies, which reported engraftment, 95% (1632/1712) of patients engrafted. Eighteen papers provided analyses of disease response in patients who had active disease at transplant. Complete and/or partial response rates for patients are shown in Table 8 according to disease.

Table 8:Response Rate of Patients Receiving High Dose Oral Busulfan According to Disease Type

The overall acute mortality for oral busulfan (through day 30) was 6.7%, for autologous transplant it was 2.6% and for allogeneic transplant it was 7.9%. Multiple factors including stage of disease, prior therapy, graft versus host disease therapy, and patient's age were reported to influence both relapse and survival.

TOXICOLOGY

An acute toxicity and two multiple-dose toxicity studies were conducted on BUSULFEX. In this acute intravenous toxicity study, male rats received single doses of 1, 5, 10, 20, or 40 mg/kg of two lots of the busulfan formulation; one representing a standard batch and one lot which underwent forced degradation. The purpose of this study was to show that potential degradation products did not affect the acute toxicity profile of the busulfan formulation. A dose of 40 mg/kg of both formulations produced mortality in all treated animals and 20 mg/kg of reference busulfan produced mortality in three of five treated animals. No other deaths occurred. Clinical signs were primarily limited to 20 mg/kg (both formulations) and included scabbing, abnormal excretion, hair loss, hypoactivity and the appearance of material on the nose, mouth, neck forelimbs and uro- and anogenital areas. Overall, the total incidence of and number of rats exhibiting clinical signs were greater in the 20 mg/kg reference busulfan group than in the 20 mg/kg degraded busulfan group. Only isolated reports of clinical effects were noted at doses of 10 mg/kg and below. In addition, body weight gain and food consumption were decreased during the first and third weeks in rats treated with 20 mg/kg reference busulfan. At necropsy, effects were noted in the lungs of animals dying during treatment and in one animal surviving treatment; isolated findings were reported in other organ systems. The LD50 for the reference busulfan formulation was 19 mg/kg, but the LD50 for the degraded formulation could not be calculated due to the mortality pattern; it was concluded to be greater than 20 and less than 40 mg/kg. Based on the clinical signs, body weight, food consumption and mortality data, the degraded busulfan formulation was less toxic than the reference formulation, possibly due to a slightly lower percentage of active drug. Two multiple dose toxicity studies have been conducted on BUSULFEX. In both, the drug was administered intravenously to beagle dogs at doses ranging from 0.25 to 4 mg/kg q.i.d. for 4 days. The highest dose produced severe toxicity expressed as hypoactivity, prostration, significant body weight loss and decreased food consumption; these effects required the animals to be euthanized. Other less severe treatment-related effects observed at doses greater than 0.25 mg/kg included decreases in body weight gain and food consumption, liver toxicity (measured as elevations in alanine aminotransferase, alkaline phosphatase, and gamma glutamyltransferase), serum chemistry changes and hematopoietic toxicity (i.e., decreased white blood cell, platelet and reticulocyte counts). No treatment-related gross or microscopic lesions were noted at necropsy. The lowest no-observable-effect-level for busulfan was 0.25 mg/kg q.i.d. Studies in mice and rats from the literature revealed that busulfan produces sterility. Spermatogonia were the primary target in males and oocytes were the target in females. In addition, exposure of pregnant rats after gestation day 11 produced virtually complete sterility in the offspring. Busulfan was teratogenic producing adverse effects on gonadal development, weight gain and the musculo-skeletal system. Busulfan was mutagenic in both in vitro and in vivo screens. Nevertheless, only "limited" evidence exists for a carcinogenic effect of busulfan treatment. Mixed results were reported in various bioassays.

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