An Automated Method for Supporting Busulfan Therapeutic Drug Monitoring

INTRODUCTION: Busulfan is a chemotherapeutic agent commonly used for myeloablative conditioning regimens such as in the treatment of chronic myelogenous leukemia. Busulfan dosing is complex due to wide interpatient variability in pharmacokinetics and a narrow therapeutic range. Although busulfan dose is normalized to body weight, therapeutic drug monitoring (TDM) using area under the plasma concentration curve is recommended after the first dose. A high busulfan area under the plasma concentration curve (>1500 μM·min) is associated with an increased risk for sinusoidal obstruction syndrome, and a suboptimal area under the plasma concentration curve (<900 μM·min) is associated with an increased risk for graft rejection or disease relapse. TDM of busulfan is not widely available due to the lack of commercially available and rapid methods to determine the area under the plasma concentration curve. METHODS: The purpose of this study was to evaluate the Roche cobas c 111 instrument, a photometric automated chemistry analyzer, using the Busulfan PCM assay from Saladax Biomedical Inc. The assay using this instrument was compared with an enzyme-linked immunosorbent assay (ELISA) from Saladax Biomedical Inc and the Olympus AU400e. Linearity and accuracy were evaluated between 175 and 1750 ng/mL. Imprecision was determined by analyzing 5 concentrations of standards twice a day for 20 days. RESULTS: Linearity for the Roche method had a slope and y-intercept of 1.050 and -5.5, respectively, and percent recovery ranged between 95% and 105%. Correlation between the Roche and ELISA platforms was analyzed by linear regression on 26 frozen patient samples. The results from the comparison of the methods based on the Roche and ELISA platforms were as follows: coefficient of determination (R2) was 0.9684, with a slope and y-intercept of 0.752 and 108.41, respectively. Correlation between the Roche and Olympus instruments was analyzed by linear regression and Bland-Altman plots. The coefficient of determination (R2) was 0.9942, with a slope and y-intercept of 1.035 and -41.3326, respectively. CONCLUSIONS: Availability of TDM of busulfan can be improved by the use of commercially available reagents and automated platforms.