Limited Sampling Strategies Supporting Individualized Dose Adjustment of Intravenous Busulfan in Children and Young Adults

BACKGROUND AND AIMS: Therapeutic drug monitoring (TDM) for busulfan supports dose adjustment during conditioning for stem cell transplantation. The authors aimed to develop and validate limited sampling strategies (LSS) of 4 to 5 samples for a precise estimation of the area under plasma concentration-time curve (AUC) for busulfan, as an alternative to an intensive sampling strategy (ISS) requiring 9 to 10 samples. METHODS: ISS TDM data from 297 patients (≤ 18 years of age) were used. AUCLSS was calculated by using the trapezoidal rule and multiple linear regression (MLR). Unlike more complex modeling methods, MLR does not require sophisticated software or advanced training for personnel. MLR coefficients were estimated in the development subset containing a randomly selected 50% of the records and were then used to calculate the AUCLSS of the remaining records (the validation subset). The agreement between dose adjustment recommendations (DAR) based on ISS and LSS, in the validation subset, was evaluated by a Bland-Altman analysis. A DAR deviating from an ISS-based reference by < 15% was deemed acceptable. RESULTS: Twelve LSSs were acceptable. Sampling at 0, 120, 180, and 240 minutes after the start of the second infusion (LSS15) yielded the best performance, with DAR deviating from the reference by < 10% for 95% of cases, and the AUCLSS was determined as follows:AUCLSS = 74.7954 × C(0) + 81.8948 × C(120) + 38.1771 × C(180) + 138.1404 × C(240) + 54.1837This LSS and LSS 13 performed similarly well in an independent external validation. CONCLUSIONS: MLR-based estimates of AUCLSS provide DARs that deviate minimally from the reference. LSSs allow the reduction of patient discomfort, a ∼50% reduction of TDM-related workload for nursing staff and blood loss and a ∼25% reduction in laboratory workload. These benefits may encourage wider use of busulfan TDM, supporting safe and efficacious personalized dosing.