Impact of dose and duration of therapy on dexamethasone pharmacokinetics in childhood acute lymphoblastic leukaemia-a report from the UKALL 2011 trial

Abstract

Introduction: The use of dexamethasone in acute lymphoblastic leukaemia therapy contributes to short- and long-term toxicities. The UKALL 2011 randomised trial investigated whether a more intense dexamethasone dose (10 mg/m²/d x 14d, short vs 6 mg/m²/d x 28d, standard) would lead to a more rapid cytoreduction and reduced adverse effects associated with longer durations of steroids in induction. The impact of dose and duration on dexamethasone pharmacokinetics was investigated.

Methods: Blood samples were obtained on one of the first three and last three days of induction dexamethasone dosing at time points up to 8 h after oral administration. Plasma dexamethasone levels were quantified in 1084 plasma samples obtained from 174 children and a population pharmacokinetic model developed.

Results: Drug exposure varied significantly between patients, with a >12-fold variation in AUC_0-12h values and a marked overlap in dexamethasone exposures between dose levels. Intuitively, AUC_0-12h was significantly higher with short dosing (10 mg/m²/d), but cumulative exposure was significantly higher with standard dosing over 28 days, after a higher cumulative dose. Concomitant rasburicase administration was associated with a 60% higher dexamethasone clearance. Day 8 bone marrow response was comparable between dosing arms, but those with <5% blast count exhibited a greater mean dexamethasone exposure than those with >5%. No statistical differences were observed between arms in terms of steroid-related toxicity or minimal residual disease at the end of induction.

Conclusion: The potential significance of dexamethasone AUC_0-12h on early response and higher cumulative exposure on the standard arm suggest that duration of therapy and exposure may be more important factors than absolute dose from a clinical pharmacology perspective.

Keywords: Acute lymphoblastic leukaemia; Dexamethasone; Paediatrics; Pharmacokinetics.