C Nilsson

The effect of busulphan on the pharmacokinetics of cyclophosphamide and its 4-hydroxy metabolite: time interval influence on therapeutic efficacy and therapy-related toxicity

Busulphan and cyclophosphamide (Bu/CP) are widely used in preparative regimens for bone marrow transplantation. Many studies have shown a wide variation in busulphan pharmacokinetics. Moreover, higher rates of liver toxicity were reported in Bu/CP protocols than in a total body irradiation (TBI)-containing regimen. In the present paper we investigated the effect of the time interval between the last dose of busulphan and the first dose of cyclophosphamide on the pharmacokinetics of CP and its cytotoxic metabolite 4-hydroperoxycyclophosphamide (4-OHCP). Thirty-six patients undergoing bone marrow transplantation (BMT) were included in the study. We also investigated the occurrence of veno-occlusive disease, mucositis and graft-versus-host disease. Ten patients conditioned with CP followed by TBI served as a control group (TBI). Twenty-six patients were conditioned with Bu/CP. The patients received Bu (1 mg/kg × 4 for 4 days), followed by CP (60 mg/kg for 2 days) administered as a 1-h infusion. Patients received their CP therapy either 7–15 h (group A, n = 12) or 24–50 h (group B, n = 14) after the last dose of Bu. None of the patients were given phenytoin or any other drug known to enhance CP metabolism. The administration of CP less than 24 h after the last dose of Bu resulted in: (1) a significantly (P = 0.003) lower clearance for cyclophosphamide was observed in group A (0.036 l/h/kg) compared to 0.055 and 0.055 l/h/kg, in the B and TBI groups, respectively; (2) significantly (P = 0.002) longer elimination half-life in group A (10.93 h) than in groups B and TBI (6.87 and 7.52 h, respectively); (3) significantly (P < 0.001) lower exposure to the cytotoxic metabolite (4-ohcp), expressed as the ratio auc4-OHCP/AUCCP, in group A (0.0053) than that obtained in group B (0.013) and group TBI (0.012); (4) the patients in group A had a significantly (P < 0.05) higher incidence of vod (seven of 12) than the other groups, b and tbi (2/14 and 1/10, respectively); and (5) mucositis was significantly higher in group a patients (8/12), being seen in only one patient in group b and none in the tbi group. the present study has shown that the interval between busulphan and cyclophosphamide administration can negatively affect the pharmacokinetics of cyclophosphamide and its cytotoxic metabolite. we conclude that the timing of cp administration must be considered in order to improve drug efficacy and reduce conditioning-related toxicity. Bone Marrow Transplantation (2000) 25, 915–924.

In vivo dynamic distribution of 131I-glucagon-like peptide-1 (7-36) amide in the rat studied by gamma camera.

The in vivo distribution of glucagon-like peptide-1 (7-36) amide (GLP-1) was studied in a rat model using radiolabeled GLP-1 (131I-GLP-1) depicted by a gamma-camera. The dynamic scan showed a rapid clearance from the blood circulation after an intravenous (i.v.) injection of 131I-GLP-1. After 10 min, the major part of the radioactivity was accumulated in the kidneys, whereas about 9% (of the blood value) was found in the brain. The pharmacokinetic study using 125I-GLP-1 demonstrated a rapid elimination from plasma, with a half-life of 3.3 +/- 0.6 min, a clearance of 117 +/- 15 mL/min, and a distribution volume of 557 +/- 61 mL. The elimination half-lives for the intact 125I-GLP-1 in lungs and kidneys were determined to 3.7 and 3.9 min, respectively. The metabolite GLP-1 (9-36) amide was followed in blood, lung, and kidney. All other organs assumed to contain low molecular weight fragments of GLP-1. The present study suggest that GLP-1 and/or its labeled metabolites cross the blood-brain barrier. Also the kidney plays an essential role in GLP-1 elimination after an i.v. administration, which can be of clinical interest especially in patients with kidney insufficiency who are treated with GLP-1.

Population pharmacokinetic analysis resulting in a tool for dose individualization of busulphan in bone marrow transplantation recipients.

The aims of the present study were (1) to investigate and quantify the pharmacokinetics, including inter-occasion variability and covariate relationships, of busulphan in BMT patients and (2) to develop a user-friendly initial dosing and therapeutic drug monitoring (TDM) strategy for the treatment of those patients with busulphan. The pharmacokinetics of busulphan was studied in 64 adults and 12 children who received busulphan (1 mg/kg) four times daily for 4 days. A one-compartment model with first order absorption and a lag time was sufficient in describing the concentration-time profile. Oral clearance (CL/F) was found to be correlated to weight (+1.2%/kg), ALT (−13%/μcat/l) and concomitant phenytoin treatment (+21%). CL/F and the volume of distribution (V/F) were estimated to 9.23 l/h and 39.3 l, respectively, in a typical individual. Inter-occasion variability (9.4%) in CL/F was estimated to be less than inter-individual variability (28%), a prerequisite for the value of TDM. Bayesian CL/F estimates based on three samples were in good accordance with those based on all samples. The final population model was implemented into the program Excel. The resulting flexible and easy to use dosing program might be used for both initial and, requiring only three plasma samples, maintenance dose individualization of busulphan therapy. Bone Marrow Transplantation (2001) 28, 657–664.

A phase I/II study of multiple-dose intravenous busulfan as myeloablation prior to stem cell transplantation

Busulfan has been previously only available in an oral formulation due to its poor water solubility. We report the results of a phase I study of multiple escalating doses of intravenous busulfan (Spartaject Busulfan, Orphan Europe, Paris, France) for myeloablation prior to stem cell transplantation (SCT) in 12 patients with chronic myeloid leukemia, acute myeloid leukemia or acute lymphocytic leukemia. One patient received allogeneic SCT; the other 11 patients received autologous SCT. The first six patients received i.v. busulfan diluted in 50 ml of 0.9% normal saline and the last six patients received busulfan in a 500-ml 5% dextrose solution. All patients experienced profound myelosuppression and all but one demonstrated hematopoietic engraftment. Toxicity was mild or moderate and there were no toxic deaths attributable to busulfan. Of note, there were no cases of veno-occlusive disease of the liver. Busulfan plasma concentrations were determined by gas chromatography with electron capture detection and showed little intra-patient variability. In most cases there was no significant difference between the first and last dose PK parameters. These data suggest that dose adjustment based on first dose PK data could allow uniformity of busulfan dosing for patients receiving SCT.

The effect of metronidazole on busulfan pharmacokinetics in patients undergoing hematopoietic stem cell transplantation

Summary:Busulfan (Bu) is an important component of some myeloablative regimens prior to stem cell transplantation (SCT). Over the last few years it has been shown that other drugs administered concomitantly can influence Bu pharmacokinetics. In the present study, we compared Bu concentrations (trough levels) in three groups of patients. Group A (n=5) received metronidazole as graft-versus-host disease prophylaxis during Bu treatment. Group B (n=9) received Bu only for 2 days followed by 2 days of Bu and metronidazole. Group C (n=10) was a control group that received Bu without metronidazole. The mean Bu levels for Group A receiving metronidazole during conditioning was significantly (P<0.001) higher (948±280 ng/ml), compared to those observed in the control group (507±75 ng/ml). In Group B, the administration of metronidazole resulted in a significant (P<0.001) increase in Bu levels (807±90 ng/ml) during the last 2 days, compared to 452±68 ng/ml during the first 2 days. In Group A, one patient died with multiorgan failure, three experienced veno-occlusive disease (VOD) and one developed hemorrhagic cystitis. Elevated liver transaminases (AST, ALT) and bilirubin were detected in all Group A patients. In Group B, six patients had elevated liver function tests but no VOD was observed. We conclude that metronidazole should not be administered simultaneously with Bu to avoid the high plasma levels of Bu, which may lead to severe toxicity and/or treatment related mortality.

Impact on the cytomegalovirus (CMV) viral load by CMV-specific T-cell immunity in recipients of allogeneic stem cell transplantation.

Patients experience cytomegalovirus (CMV) reactivation after stem cell transplantation (SCT) and need repeated courses of pre-emptive therapy. Analysis of CMV-specific immunity might help to assess the need for antiviral therapy. Forty-eight patients were studied during the first 3 months after SCT. Peripheral blood lymphocytes were stimulated by CMV antigen, and interferon (INF)-γ production by CD3+ and CD4+ T cells was analysed. Results were correlated to transplant factors and CMV disease. Patients with INF-γ production by CD3+ cells at 4 weeks after SCT had lower peak viral loads than patients with no such production (P=0.03). There was a similar tendency as regards CD4+ cells (P=0.09). Patients who underwent reduced-intensity conditioning (RIC) more frequently had CD3+ (48%) and CD4+ immunity (56%) 4 weeks after SCT compared with patients who received myeloablative conditioning (CD3+ 25%; CD4+ 35%). There was no effect of stem cell source, donor type or acute graft-versus-host disease. Three of 48 patients developed CMV disease and none of them had detectable INF-γ production. CMV-specific T-cell response is associated with a lower rate of CMV replication. RIC results in improved T-cell reconstitution. Recovery of CMV-specific immunity might be delayed in patients with CMV disease. These observations suggest that detection of CMV-specific T-cells is useful in assessing the immunity against CMV.

Pharmacokinetics of liposomal busulphan in man

High doses of busulphan are used in conditioning regimens before stem cell transplantation. Great inter-patient variations in pharmacokinetics and a correlation between toxicity and high systemic exposure of busulphan have been shown in several studies. Some authors have suggested therapeutic drug monitoring and intravenous busulphan aiming to reduce the conditioning-related toxicity. Liposomal busulphan (LBu) might be an alternative to intravenous administration of high-dose busulphan in conditioning. In the present study, we investigated the pharmacokinetics of LBu in man. Seventeen consecutive patients were enrolled in the study. LBu as a single low dose (2 to 8 mg) was given to 12 patients (six adults and six children). Five patients received two high doses of LBu which replaced the first and the last doses of the conditioning regimen. The high dose of LBu was raised from 0.4 to 0.9 mg/kg. A significant linear correlation (r2 = 0.928) was found between the dose of LBu and the area under the plasma concentration-time curve (AUC) (P < 0.001). AUC corrected for 1 mg/kg was 5491 ± 912 ng·h/ml and 5955 ± 627 ng·h/ml (low dose of LBu in children and adults, respectively) and 6167 ± 1385 ng·h/ml and 6933 ± 656 ng·h/ml (ie the first and the last high doses of LBu, respectively). No significant correlation was found between clearance and age or apparent volume of distribution and age (r2 = 0.146 and r2 = 0.046, respectively). No toxicity related to the liposomal formulation of busulphan was observed. We conclude that LBu is suitable for conditioning before stem cell transplantation. Bone Marrow Transplantation (2001) 27, 479–485.

Liposomal busulphan: bioavailability and effect on bone marrow in mice

High-dose busulphan is an important component of many BMT conditioning regimens. High-dose busulphan therapy is associated with an increased risk of acute toxicity such as CNS toxicity and veno-occlusive disease (VOD). The toxicity was reported to correlate with a high AUC (area under the curve) during therapy. An intravenous form of busulphan would overcome the problems caused by inter-individual variability and bioavailability of busulphan and most probably minimize the problems with dose adjustment during therapy. The liposomal form of busulphan is an attractive alternative for intravenous administration of busulphan. In the present study, we compared the myeloablative effect of liposomal busulphan (LB) with that of the oral administration form and busulphan dissolved in organic solvent (Bus/DMSO) in mice. The pharmacokinetics of LB and Bus/DMSO were described by one compartment model while the oral data were fitted to one compartment model with first order absorption. The bioavailability of LB was 0.86 ± 0.02 compared to that obtained after the oral administration (0.40–0.74). Myelosuppression was determined using the colony-forming unit granulocyte–macrophage assay (CFU-GM) on days 1, 3, 6 and 9 after the conditioning regimen. LB resulted in significant myelosuppression from day 1 to day 9. The decrease in CFU-GM after conditioning regimen with LB was not significantly different from that observed after oral busulphan. Moreover, the administration of liposomes only to the mice did not affect the bone marrow. No side-effects of the liposomal formulation were observed. We suggest that the novel form of busulphan is a promising drug for clinical use.

A phase II trial of liposomal busulphan as an intravenous myeloablative agent prior to stem cell transplantation: 500 mg/m 2 as a optimal total dose for conditioning

We conducted a phase I/II trial, to evaluate the efficacy and safety of an intravenous liposomal formulation of busulphan (LBu) as a myeloablative agent for stem cell transplantation (SCT). The liposomal busulphan was administered as a 3 h infusion twice daily over 4 consecutive days. Six adults received 1.6–2 mg/kg/dose and 18 children received 1.8–3 mg/kg/dose. Pharmacokinetic parameters were studied after the first and the last dose of busulphan. No significant difference in clearance, AUC, elimination half-lives or distribution volume between the first and the last dose was found in either groups. A significantly (P < 0.005) higher clearance was observed in children after the first and the last dose (3.61 and 3.79 ml/min/kg, respectively) compared to adults (2.40 and 2.33 ml/min/kg, respectively). The elimination half-lives after the first and the last dose were significantly (P < 0.005) shorter in children (2.59 and 2.72 h, respectively) compared to adults (3.35 and 3.61 h, respectively). Clearance correlated significantly with age. However, no significant correlation with age was observed when clearance was adjusted to the body surface area. Two cases of VOD following a total dose of 24 mg/kg were observed. Six patients experienced mucositis. No other organ toxicity was observed. We conclude that intravenous liposomal busulphan pharmacokinetics is age dependent. A dosage schedule based on body surface area should be used especially in young children to reduce the age-dependent difference in kinetics. An intravenous liposomal dose of busulphan of 500 mg/m2 is suggested to reach a similar systemic exposure and myeloablative effect in both children and adults. Moreover, the novel liposomal form of busulphan showed a favorable toxicity profile and seems safe as a part of the high-dose therapy prior to SCT.

Pharmacokinetics and distribution of liposomal busulfan in the rat: a new formulation for intravenous administration.

Abstract The plasma pharmacokinetics and tissue distribution of busulfan (Bu) were investigated after intravenous injection of free Bu (D-Bu) and freshly prepared liposomal Bu (L-Bu). Liposomal Bu was prepared using l-α-phosphatidylcholine, 1,2-dioleolyl-sn-glycero-3-phosphate, and cholesterol. The liposomes formed were unilamellar vesicles measuring 220 ± 14 nm in diameter and containing a Bu concentration of 0.31 ± 0.03 mg/ml. The half-life of Bu in the present formulation was determined to be 8.7 ± 2.7 days at 4 °C. The liposomes in the new formulation were stable for 20 days at 4 °C. After the intravenous administration of L-Bu or D-Bu (dissolved in a mixture of DMSO, ethanol, and propylene glycol) to the rats a higher bone marrow exposure to Bu as expressed in AUC marrow/AUC blood was achieved using L-Bu as compared with D-Bu (1.59 and 0.83, respectively). A higher distribution volume was observed for L-Bu as compared with D-Bu (1.39 versus 0.67 l/kg, respectively). The elimination half-lives were significantly longer in both blood and marrow after the administration of L-Bu as compared with D-Bu (2.52 and 3.08 versus 1.53 and 1.75 h, respectively). The new liposomal Bu showed linear pharmacokinetics within the range of 0.5–3.5 mg/kg, which is comparable with that obtained for D-Bu. A slight difference was observed in systemic exposure to L-Bu as compared with D-Bu as expressed in AUC (9.93 and 11.82 μg h ml−1, respectively). The distribution study using 14C-labeled Bu showed that the radioactivity was significantly higher over 18 h in the bone marrow (3-fold) and spleen (2-fold; P < 0.01) in a comparison of L-Bu with D-Bu. However in the brain, lungs, and heart the distribution of radioactivity after the administration of L-Bu was significantly lower (P < 0.05) than that␣obtained using D-Bu. On the basis of the present study, the new formulation of liposomal Bu seems to be a promising preparation for clinical trails, since it appears to target bone marrow and spleen with no accumulation in the liver or other organs known for Bu toxicity.