Busulfan.

OBJECTIVE: To review the current published studies evaluating the pharmacokinetics, clinical efficacy, safety, and toxicity of busulfan in pediatric and adult patients. DATA SOURCES: English-language literature published between 1953 and 1993 was analyzed; pertinent literature was reviewed. STUDY SELECTION: Emphasis was placed on pharmacologic studies and clinical trials involving busulfan therapy both in myeloproliferative disorders and in conditioning regimens for autologous or allogeneic bone marrow transplantation. DATA EXTRACTION: Data from both pediatric and adult studies were evaluated; emphasis was placed on the relationship between plasma concentrations of busulfan and its efficacy and toxicity. DATA SYNTHESIS: Busulfan has been used widely at conventional dosages (1-12 mg/d) for the treatment of patients with chronic myelogenous leukemia (CML). Busulfan at high doses (usually 16 mg/kg) given with other cytotoxic drugs (especially cyclophosphamide) is a common preparative regimen in patients undergoing allogeneic or autologous bone marrow transplantation (BMT) for acute or chronic leukemia and other nonmalignant disorders (e.g., hemoglobinopathies, inborn error of immune system, congenital metabolic disorders). Pharmacokinetics of high-dose busulfan are age-dependent. Busulfan systemic exposure and, thus, tissue and tumor exposure are lower in children than with adults. Relationships between toxicity (principally neutropenia, hepatic veno-occlusive disease, incidence of seizures) and drug exposure were found for busulfan. CONCLUSIONS: Busulfan is a useful, sufficiently safe drug in the treatment of patients with CML. At higher dosages, busulfan is a fundamental part of myeloablative therapies for patients undergoing BMT. As the pharmacokinetics and metabolism of busulfan is further understood, there is great potential for improving treatment outcome. An assessment of maximal tolerated exposure determined by therapeutic drug monitoring may decrease the incidence and lethality of regimen-related toxicities.

High-performance liquid chromatographic-mass spectrometric assay of busulfan in serum and cerebrospinal fluid.

A liquid chromatographic-mass spectrometric method has been developed to determine busulfan concentrations in the cerebrospinal fluid and serum of some children undergoing bone marrow autotransplantation. After two liquid-liquid extraction steps with dichloromethane on a biological matrix, the separation of busulfan was carried out by isocratic reversed-phase chromatography. The mass spectrometric system was operated in electron-impact mode. Principal ions at m/z 175, 111 and 79 were observed for busulfan, but only m/z 175 was chosen for the quantification of the analyte. The retention time of busulfan was 2.5 min. The detection limit of 100 ng/ml allowed the determination of cerebrospinal fluid and serum busulfan concentrations during the four days of high-dose (1 mg/kg) treatment prior to autotransplantation in five child patients.

Dose-dependent neurotoxicity of high-dose busulfan in children: a clinical and pharmacological study.

Busulfan is known to be neurotoxic in animals and humans, but its acute neurotoxicity remains poorly characterized in children. We report here a retrospective study of 123 children (median age, 6.5 years) receiving high-dose busulfan in combined chemotherapy before bone marrow transplantation for malignant solid tumors, brain tumors excluded. Busulfan was given p.o., every 6 hours for 16 doses over 4 days. Two total doses were consecutively used: 16 mg/kg, then 600 mg/m2. The dose calculation on the basis of body surface area results in higher doses in young children than in older patients (16 to 28 mg/kg). Ninety-six patients were not given anticonvulsive prophylaxis; 7 (7.5%) developed seizures during the 4 days of the busulfan course or within 24 h after the last dosing. When the total busulfan dose was taken into account, there was a significant difference in terms of neurotoxicity incidence among patients under 16 mg/kg (1 of 57, 1.7%) and patients under 600 mg/m2 (6 of 39, 15.4%) (P less than 0.02). Twenty-seven patients were given a 600-mg/m2 busulfan total dose with continuous i.v. infusion of clonazepam; none had any neurological symptoms. Busulfan levels were measured by a gas chromatographic-mass spectrometry assay in the plasma and cerebrospinal fluid of 9 children without central nervous system disease under 600 mg/m2 busulfan with clonazepam:busulfan cerebrospinal fluid:plasma ratio was 1.39. This was significantly different (P less than 0.02) from the cerebrospinal fluid:plasma ratio previously defined in children receiving a 16-mg/kg total dose of busulfan. This study shows that busulfan neurotoxicity is dose-dependent in children and efficiently prevented by clonazepam. A busulfan dose calculated on the basis of body surface area, resulting in higher doses in young children, was followed by increased neurotoxicity, close to neurotoxicity incidence observed in adults. Since plasma pharmacokinetic studies showed a faster busulfan clearance in children than in adults, this new dose may approximate more closely the adult systemic exposure obtained after the usual 16-mg/kg total dose, with potential inferences in terms of anticancer or myeloablative effects. The busulfan dose in children and infants undergoing bone marrow transplantation should be reconsidered on the basis of pharmacokinetic studies.

Cerebrospinal fluid and plasma concentrations of busulfan during high-dose therapy.

A patient with acute myeloblastic leukemia received high-dose busulfan (1 mg/kg by mouth every 6 h for 4 days) as myelo-ablative therapy for autologous bone marrow transplantation. Rapid entry of busulfan into the cerebrospinal fluid (CSF) was observed. Plasma and CSF concentrations of busulfan were comparable during the 4 days of treatment. The elimination half-lives of busulfan in plasma and CSF were 2.6 h and 2.8 h respectively during the first 12 h after the last dose.