The effect of low dose Ara‐C in acute non‐lymphoblastic leukaemias and atypical leukaemia

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Abstract
Nine patients with nonlymphocytic leukemia and 1 patient with refractory anemia with excess of blasts (RAEB) were treated s.c. with Ara-C [cytosine arabinoside] at a low dose of 10 mg/m2 12 h; complete remission was obtained in 7 patients. In all cases severe pancytopenia was observed during treatment. The concentration of Ara-C was measured in serum, and found that the maximum concentration reached a peak (52-132 ng/ml; mean 84.2 ng/ml) at 15 min following injection. These concentrations can be considered sufficient to inhibit DNA synthesis. Primary short-term culture of human leukemic cells with low dose Ara-C was also performed, and differentiation of leukemic cells was observed for several types of leukemic cells. The in vitro findings corresponded to the observed clinical effects. From the above results, the action of low dose Ara-C may have resulted from a combination of 2 different mechanisms, its cytostatic effect and its differentiation-inducing effect.