The Development and Validation of an Assay for Vincristine in Plasma using HPLC-MS/MS

Background: The development and validation of a rapid and sensitive high performance liquid chromatography-tandem mass spectrometry (HPLCMS/ MS) method using atmospheric pressure chemical ionization (APCI) is described. Sample preparation is a single-step addition of acetonitrile, then reconstitution of the dried supernatant in mobile phase. The injection volume is 100 mL. Vincristine sulfate (VS) and the internal standard (IS) vinblastine sulfate, are eluted at 2.26 min and 2.31 min, respectively, without interference from endogenous substances or co-medications. Linearity (r2 $ 0.999) was established between 0.1 and 20 mg/L and the lower limit of quantitation (LLOQ) was 0.2 mg/L, based a priori on estimates of imprecision and inaccuracy. Application of the assay in pharmacokinetic studies in young children with leukaemia was demonstrated. VS was administered by a 1 min intravenous push to 2 infants aged 15 months and 21 months who had acute lymphoblastic leukaemia (ALL). Plasma VS concentrations from blood sampled up to 48 h post-dose were assayed by the described procedure. The pharmacokinetic data were analysed using a model-independent approach [Gibaldi, 1991). Clearance (CL), volume of distribution at steady-state (Vss), mean residence time (MRT), and terminal elimination half-life (t0.5). To our knowledge, these are the youngest reported patients for which VS disposition has been studied. The median pharmacokinetic parameters were; CL: 254 mL/min/m2 (0.810 L/h/kg); Vss: 337 L/m2 (17.6 L/kg); MRT: 22.7 h; t0.5 : 21.1 h. For comparison, the CL, Vss and t0.5 reported in older children of median age 4.5 y were 362 mL/min/m2, 445 L/m2 and 16.9 h, respectively (Frost, B.M. et al, Acta Pædiatr. 2003;92:551). These results established the suitability of the assay to estimate the pharmacokinetics of VS in infants on VS chemotherapy