Individual dose adjustment of oral busulfan using a test dose in hematopoietic stem cell transplantation.

Maintaining the appropriate average steady-state plasma concentrations (Css) of busulfan (BU) is critical for both successful engraftment and minimizing toxicity in hematopoietic stem cell transplantation (HST). We therefore performed a prospective trial with 50 adult Japanese patients that involved adjusting the BU dose in accordance with individual BU pharmacokinetics (PK). After administering a 0.5-mg/kg test dose of oral BU, we analyzed individual BU PK parameters and calculated an adjusted BU dose that would achieve a target BU Css of 850 ng/mL. Thirty-nine patients (78%) required a BU dose decrease, and the median adjusted BU dose was 0.81 mg/kg (range, 0.51-1.29 mg/kg). All patients who underwent allogeneic HST received the adjusted BU dose. After administering the sixth BU dose, we measured the plasma BU concentration. The actual BU concentration was significantly correlated with the expected BU concentration, and the predictability of the BU Css was 103% +/- 9%. The incidence of toxicity excluding oral mucositis was low, and there was no regimen-related toxicity-associated mortality. Engraftment was achieved in 98% of the patients. This study showed that our method for adjusting the BU dose facilitated reliable prediction of the actual BU Css and that individualized BU dose adjustment was able to improve clinical outcomes in HST recipients treated with a BU-containing conditioning regimen.

Rapid and sensitive HPLC method for the simultaneous determination of paraquat and diquat in human serum.

A rapid and sensitive HPLC method for the simultaneous determination of paraquat and diquat in human serum has been developed. After deproteinization of the serum with 10% trichloroacetic acid, the samples were separated on a reversed-phase column, and subsequently reduced to their radicals with alkaline sodium hydrosulfite solution. These radicals were monitored with a UV detector at 391 nm. This method permitted the reliable quantification of paraquat over linear ranges of 50 ng - 10 microg/ml and 100 ng - 10 microg/ml for diquat in human serum. The within- and between-day variations are lower than 2.3 and 2.2%, respectively. This technique was also utilized to determine the paraquat and diquat serum levels in a patient who had ingested herbicide (Prigrox L) containing paraquat and diquat.

Population pharmacokinetic study of a test dose oral busulfan in Japanese adult patients undergoing hematopoietic stem cell transplantation.

PURPOSE: The aim of this study is to determine the population pharmacokinetics of oral busulfan in Japanese adults. METHODS: We previously underwent a clinical trial involving the dose adjustment of oral busulfan depending on the individual pharmacokinetics using a test dose in hematopoietic stem cell transplantation recipients. Seventy-one Japanese patients aged from 16 to 67 years were enrolled. After taking oral busulfan 0.5 mg/kg as a test dose, blood samples were collected at five time points from each patient. Busulfan concentrations were measured by high-performance liquid chromatography, and the individual parameters were estimated by using the nonlinear mixed effects model computer program. A one-compartment model with first-order absorption was sufficient to describe the concentration-time profile. RESULTS: The final pharmacokinetic parameter were the clearance (CL/F) = 0.153 L/h/kg, distribution volume (Vd/F) = 0.695 L/kg, and absorption rate constant (ka) = 2.39 h(-1). The inter-individual variabilities in CL/F, Vd/F and ka were 25.9, 26.2, and 111.8%, respectively, and the residual variability was 12.1% as the coefficient of variation. CONCLUSION: We developed a population pharmacokinetic model of oral busulfan in Japanese adults. The final population model was implemented into the program excel, leading to an easy and proper therapeutic monitoring of oral BU by using small number of samples.