Activity and toxicity of intramuscular 1000 iu/m2 polyethylene glycol‐E. coli L‐asparaginase in the UKALL 2003 and UKALL 2011 clinical trials

Summary In successive UK clinical trials (UKALL 2003, UKALL 2011) for paediatric acute lymphoblastic leukaemia (ALL), polyethylene glycol‐conjugated E. coli L‐asparaginase (PEG‐EcASNase) 1000 iu/m2 was administered intramuscularly with risk‐stratified treatment. In induction, patients received two PEG‐EcASNase doses, 14 days apart. Post‐induction, non‐high‐risk patients (Regimens A, B) received 1–2 doses in delayed intensification (DI) while high‐risk Regimen C patients received 6–10 PEG‐EcASNase doses, including two in DI. Trial substudies monitored asparaginase (ASNase) activity, ASNase‐related toxicity and ASNase‐associated antibodies (total, 1112 patients). Median (interquartile range) trough plasma ASNase activity (14 ± 2 days post dose) following first and second induction doses and first DI dose was respectively 217 iu/l (144–307 iu/l), 265 iu/l (165–401 iu/l) and 292 iu/l (194–386 iu/l); 15% (138/910) samples showed subthreshold ASNase activity (