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.