Background and methods: Seventeen adult patients with acute lymphoblastic leukemia (ALL) treated with L-asparaginase (20,000 IU/m2 on six alternate days) were infused with antithrombin III (AT III) concentrates (Kybernin P, Behring). Substitution therapy was aimed at increasing the reduced AT III concentration usually found in these patients, since AT III deficiency is thought to be associated with an increased risk of thrombosis. Two schedules of AT III administration, different in dosage, timing and duration were evaluated. The first 7 patients (group A) received a fixed dose of 2,000 U every day for 6 times, starting with the second L-asparaginase (L-ase) infusion, independently of their plasma AT III levels. In the following 10 patients (group B), 20-25 U/Kg b.w. were administered daily for 7 times only when the plasma AT III level was lower than 60% with plasma fibrinogen higher than 100 mg/dl and platelet count higher than 50 x 10(9)/l, or when AT III was below 40%. Thirteen patients who received L-ase without AT III substitution served as controls.
Results and conclusions: Both substitution regimens resulted in mean plasma AT III nadir values significantly (p less than 00.1) higher than in the controls. Our data suggest that, in ALL patients receiving L-ase according to the L20 protocol, satisfactory plasma AT III levels may be assured with infusions of 20-25 U/Kg b.w./day for 7-10 days, starting by day 2 of L-ase treatment.