Daily Weight-Based Busulfan with Cyclophosphamide and Etoposide Produces Comparable Outcomes to Four-Times–Daily Busulfan Dosing for Lymphoma Patients Undergoing Autologous Stem Cell Transplantation

High-dose busulfan (Bu) is an integral component of commonly used preparative regimens for both allogeneic and autologous transplantation. There is significant interest in comparing the efficacy and toxicity of administering Bu every 6 (Bu6) or every 24 hours (daily Bu). To facilitate a therapeutic dose-monitoring protocol, we transitioned from Bu6 to daily Bu dosing for patients with Hodgkin and non-Hodgkin lymphoma undergoing autologous stem cell transplantation (ASCT). Here, we retrospectively review outcomes of 400 consecutive eligible lymphoma patients who underwent ASCT from 2007 to 2013 with high-dose busulfan (Bu), cyclophosphamide (Cy), and etoposide (E). Bu was given at a fixed dose of either .8 mg/kg every 6 hours for 14 doses for 307 patients or a fixed dose of 2.8 mg/kg every 24 hours for 4 doses (days −9 through −6) for 93 patients who underwent transplantation after the transition from Bu6 to daily Bu was made. Toxicity was assessed using pulmonary and liver function tests (LFT) at specified time points before and after ASCT. Baseline patient and disease characteristics of patients dosed with Bu6 and daily Bu were similar. There was no significant difference in forced expiratory volume in 1 second or diffusing capacity of the lungs for carbon monoxide before and after transplantation in the Bu6 versus daily Bu cohorts. Changes in LFTs with daily Bu were not significantly different than those with Bu6. There were no differences in relapse, nonrelapse mortality, progression-free survival, or overall survival between Bu6 and Bu 24 administration schedules in univariable or multivariable analysis (P ≥ .34). For a subset of 23 patients who had first-dose Bu levels measured, we observed significant variation in an median estimated cumulative area under the curve (AUC) of 17,568 µM-minute (range, 12,104 µM-23,084 µM-minute). In conclusion, daily Bu with Cy/E is more convenient than Bu6, has equivalent outcomes, and results in no increase in either hepatic or pulmonary toxicity. Consistent with previous reports, there is a significant range of Bu AUC levels, with a standard deviation of 13%. These data provide rationale for our prospective clinical trial of real-time therapeutic dose monitoring of Bu.