Therapeutic Dose Monitoring of Busulfan Is Associated with Reduced Risk of Relapse in Non-Hodgkin Lymphoma Patients Undergoing Autologous Stem Cell Transplantation.

Optimal administration of busulfan (Bu) is hampered by variable and unpredictable drug metabolism in individual patients. At our institution, Bu was previously administered with fixed weight-based dosing (WBD) in combination with cyclophosphamide (Cy) and etoposide (E) for patients with non-Hodgkin lymphoma (NHL) undergoing autologous stem cell transplantation (ASCT). In 2014, we adopted real-time pharmacokinetic (PK)-guided therapeutic drug monitoring (TDM) of Bu for all NHL patients undergoing Bu-containing ASCT. Here we compare outcomes of NHL patients who underwent ASCT with Bu/Cy/E using WBD and those who did so using TDM of Bu. We studied 336 consecutive adult NHL patients who underwent ASCT with Bu/Cy/E using WBD from January 2007 to December 2013 (n = 258) or TDM from May 2014 to December 2017 (n = 78), excluding patients with mantle cell lymphoma. Clinical outcomes, including relapse, nonrelapse mortality (NRM), progression-free survival (PFS), and overall survival (OS), hepatotoxicity and pulmonary toxicity were compared in the 2 groups. To adjust for differences in baseline characteristics between the groups, propensity-matched cohorts of WBD and TDM patients were also studied. After the first dose of Bu, the dose was increased in 36% of the patients and decreased in 41%. Changes in pulmonary and liver function from baseline to transplantation were not different between the 2 groups, although these changes showed significantly less variability with TDM than with WBD. Relapse was significantly lower and PFS was improved with TDM; 2-year estimates were 19% for TDM and 38% for WBD for relapse (P = .004) and 69% and 55%, respectively, for PFS (P = .038). No significant between-group differences in NRM or OS were seen. In multivariable analysis, TDM remained prognostic for lower risk of relapse (hazard ratio [HR], .52; 95% confidence interval [CI], .30 to .89; P = .018), but did not remain prognostic for PFS (HR, .74; 95% CI, .48 to 1.16; P = .19). Propensity-matched cohorts displayed similar patterns of outcomes. In subset analysis based on disease status at ASCT, TDM was associated with less relapse and better PFS than WBD for patients who underwent transplantation in less than complete remission (CR) compared with those who underwent transplantation in CR. Compared with WBD, PK-directed TDM of Bu reduces the incidence of relapse when used in combination with Cy and E for patients with NHL undergoing ASCT, particularly for patients in less than CR. These data support the continued use of personalized PK-guided dosing for all NHL patients undergoing ASCT with Bu-containing preparative regimens.