No abstract

Alterations in hemostasis leading to symptomatic thromboembolism have been observed in patients with acute lymphoblastic leukemia (ALL) receiving Escherichia coli asparaginase (CASP) combined with steroids. Moreover, hereditary prothrombotic risk factors are associated with an increased risk for venous thromboembolism in pediatric ALL patients treated according to the BFM 90/95 protocols (including CASP combined with prednisone during induction therapy). To assess whether the thromboembolic risk associated with established prothrombotic risk factors is modified by treatment modalities (prednisone or dexamethasone), the present analysis was performed. Three hundred thirty-six consecutively recruited leukemic children treated according to different BFM protocols (PRED group, n ‫؍‬ 280, 60 mg/m 2 prednisone; DEXA group, n ‫؍‬ 56, 10 mg/m 2 dexamethasone during induction therapy) were studied. Study end point was the onset of symptomatic vascular accidents during induction therapy. Cumulative thromboembolism-free survival was significantly reduced in children in the PRED group (thrombosis frequency, 10.4%) compared with children in the DEXA group (thrombosis frequency, 1.8%; P ‫؍‬ .028). Although no significant difference was found in the overall prevalence of prothrombotic risk factors, 46.5% of patients in the PRED group who experienced thromboembolic events were carriers of a prothrombotic risk factor, whereas no carrier in the DEXA group had a thromboembolism. At the time of maximum CASP activity, fibrinogen and activities of antithrombin, plasminogen, and protein S were significantly reduced in the PRED group. No significant correlation could be found between CASP activity and levels of coagulation factors. In conclusion, the use of dexamethasone instead of prednisone, administered with CASP, significantly reduced the onset of venous thromboembolism. (Blood. 2003;101:2529-2533)

The enzyme asparaginase is an important element in the therapy of acute lymphoblastic leukaemia (ALL). The usual asparaginase dose as prescribed in the ALL‐BFM‐86/90 treatment protocol for the therapy of ALL is 10 000 IU/m2 at 3 d intervals and had been developed on the basis of the E. coli asparaginase preparation CrasnitinTM from the Bayer company. Using the described schedule the E. coli asparaginase preparation from the Medac company shows significantly higher biological activity than the Bayer preparation. These findings prompted an attempt to reduce the dose of the Asparaginase medacTM under careful pharmacokinetic and pharmacodynamic monitoring. At the first step of dose reduction in ALL treatment protocol I, 11 children received 5000 IU/m2 of Asparaginase medacTM. Another 15 children were given 2500 IU/m2 of the enzyme at the second step of dose reduction. Prior to each asparaginase dose, blood samples were taken to determine amino acids and trough enzyme activity. Concurrent with the asparaginase monitoring, the coagulation parameters were measured. 96% of samples from the first step of dose reduction (5000 IU/m2 every third day) showed complete L‐asparagine depletion (<0.1 μM), the median trough enzyme acitivity was 265 IU/l. At the second step of dose reduction (2500 IU/m2) complete L‐asparagine depletion was seen in 97% of samples, and the median trough enzyme acitivity was 102 IU/l. Cerebrospinal fluid (CSF) depletion was complete in all samples tested (11/11).  We concluded that an Asparaginase medacTM dose reduced from the usual 10000 IU/m2 down to 5000 IU/m2 or 2500 IU/m2, applied at 3 d intervals, was sufficient to achieve complete L‐asparagine depletion in serum. Changes of the fibrinogen levels was significantly less pronounced in the group on 2500 IU.

Native forms of asparaginase stem from different biological sources. Previously reported data from children treated with Erwinase showed significantly lower trough levels and pharmacokinetic dose intensity than after E. coli-derived preparations. Hence, schedule optimization was initiated to achieve relevant serum activities. 21 children on reinduction therapy received Erwinase on Mondays, Wednesdays and Fridays for 3 weeks (9 x 20000 IU/m2 i.v.) instead of 4x 10 000IU/m2 of E. coli asparaginase (twice weekly for 2 weeks). Asparaginase trough activities were measured as the primary parameter, targeting 100-200 IU/I after 2 d and >50 IU/l after 3 d. Concurrently, asparagine trough concentrations were monitored. The mean trough activity was 156+/-99 IU/l, with 2/108 samples showing no detectable activity. Regarding trough levels per individual (three or more measurements/patient), means ranged from 52+/-29 to 276+/-114 IU/l (20 patients, 106 samples), with nine, six, and five children inside, below, and above the target range, respectively. The mean 3 d trough activity was 50+/-39 IU/l (20 patients, 51 samples). In 11 of these samples no activity was measurable. Mean trough activities calculated per individual ranged from < 20-84+/-30 IU/l (14 patients, 42 samples) with seven children below the target limit of 50 IU/l and asparagine concentrations <0.2 - 1.5microM. We concluded that an increased dose of 9x20000 IU/m2 of Erwinia asparaginase within 3 weeks resulted in a pharmacokinetic dose intensity comparable to former observations made with 4 x 10 000IU/m2 of the E. coli product Crasnitin which is no longer marketed. High interindividual variability and the phenomenon of 'silent' inactivation necessitate monitoring wherever possible.