Abstract CT115: Pharmacokinetics of standard versus short high-dose dexamethasone therapy in childhood acute lymphoblastic leukemia: results from the UKALL 2011 trial

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Abstract Dexamethasone (Dex) is a key component of ALL therapy, with glucocorticoid sensitivity strongly linked to prognosis. However, it also contributes to life threatening toxicities. The ongoing UKALL 2011 trial is investigating a new schedule of Dex (10mg/m2 × 14 days vs 6mg/m2 × 28 days), in an attempt to bring about a more rapid cytoreduction whilst limiting toxicities associated with long term steroid exposure. There are limited data regarding Dex pharmacokinetics, however large variability has been reported in children with ALL (Yang et al. 2008). For Dex pharmacokinetic studies, blood samples were collected up to 8h post oral administration on one of the first and last three days of induction chemotherapy. Plasma Dex levels were analysed using a validated LC-MS method, with a range of 5-250ng/ml, and non-compartmental pharmacokinetic analysis was performed. Pharmacokinetic parameters from day one sampling are shown below. Exposure, as defined by AUC0-12h, and Cmax were significantly higher on the short arm (p = 0.0002 and 0.0007, respectively). However there was substantial overlap between the two arms, with a number of patients on the standard arm exhibiting higher exposures than those on short therapy, despite having a longer duration of treatment. This is reflected in the AUC0-12h ranges observed on the two arms (short: 202-1606; standard: 38-1009 hr*ng/mL). Pharmacokinetic profiles also differed between the two days of treatment, with AUC0-12h being significantly higher at the end of induction chemotherapy (n = 37, study day 1: 655 ± 322; study day 2: 894 ± 496 hr*ng/mL, p = 0.003). Based on these preliminary data it will be important to consider pharmacokinetic variability when analysing the results generated from the UKALL 2011 trial. Further evaluation of relationships between pharmacokinetic variation, dose scheduling and clinical outcome may enable better stratification of Dex therapy for future patients. Dexamethasone pharmacokinetics in short and standard therapy arms following day one samplingPharmacokinetic parameters (mean ± SD)Half life (hr)Tmax (hr)Cmax(ng/mL)Clearance(L/hr/m2)AUC0-12h(hr*ng/mL)Short (n=43)3.96 ± 3.21.9 ± 1.0128 ± 558.1 ± 5.3692 ± 325Standard (n=33)3.68 ± 2.11.7 ± 1.187 ± 419.2 ± 12.7443 ± 202 Citation Format: Rosanna K. Jackson, Julie AE Irving, Gareth J. Veal. Pharmacokinetics of standard versus short high-dose dexamethasone therapy in childhood acute lymphoblastic leukemia: results from the UKALL 2011 trial. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT115.