Monitoring of Erwinia asparaginase therapy in childhood ALL in the Nordic countries

Aims  Evaluation of l ‐asparaginase therapy in the NOPHO‐92 ALL‐protocol (treatment protocol of acute lymphoblastic leukaemia of the Nordic Society of Paediatric Haematology and Oncology, initiated in 1992) after intravenous and intramuscular administration of Erwinia asparaginase during induction and re‐induction therapy.Methods Forty children with newly diagnosed acute lymphoblastic leukaemia received Erwinia asparaginase (30 000 IU/m 2 i.v. or i.m.) during induction therapy (every day for 10 days), and 19 children received Erwinia asparaginase (30 000 IU/m 2 i.v. or i.m.) during re‐induction therapy (twice a week for 2 weeks). Within the treatment periods asparaginase trough activity (using a spectrophotometric assay) was determined on specific days. The goal of therapy is complete l ‐asparagine depletion, which asparaginase activities above 100 IU l −1 have been shown to ensure. Therefore determination of l ‐asparagine (using a h.p.l.c. method) was performed only in plasma samples with asparaginase activities below 100 IU l −1 . Results  During induction therapy 92.2% of the trough enzyme activities were above 500 IU l −1 for the i.v.‐treated patients, and 92.4% of the trough enzyme activities were above 500 IU l −1 for the i.m.‐treated patients. During re‐induction therapy 64.7% of the trough enzyme activities were below 100 IU l −1 in the i.v.‐treated group, and 73.3% of the trough enzyme activities were below 100 IU l −1 in the i.m.‐treated group. For trough enzyme activities below 100 IU l −1 l ‐asparagine depletion was complete in two thirds of the samples. Conclusions  In the NOPHO‐92 ALL‐protocol l ‐asparaginase treatment during induction therapy was unnecessarily intense, but during the re‐induction phase it appeared inadequate.