[The clinical effect of low-dose Ara-C in patients with refractory acute nonlymphocytic leukemia and myelodysplastic syndrome].

Twenty-one patients with refractory acute nonlymphocytic leukemia (ANLL) and myelodysplastic syndrome were treated with low-dose cytosine arabinoside (LDARC). LDARC was administered by subcutaneous injection every 12 hours at a dose of 10 mg/m2 (regimen A) or at a dose of 20 mg/m2 by continuous intravenous infusion (CIV) or continuous subcutaneous injection (CSC) (regimen B). Among 22 courses, two elderly patients with ANLL (M4 and M5) and one M4 patient with myelofibrosis obtained complete remission (CR) and three elderly patients with ANLL (one M1 and two M2) and one patient with ANLL developed from RAEB in transformation obtained partial remission (PR). The overall remission rate (CR + PR) was 31.8%. The CR durations were 2.5, 5 and 2 months, respectively. The plasma concentration of Ara-C determined in regimen B was 8.26 +/- 4.12 ng/ml. There was no difference in the plasma concentration of Ara-C between CIV and CSC. We consider that the major mode of action of LDARC lies in its cytotoxic effect, since all patients who obtained remission exhibited pancytopenia and bone marrow hypoplasia. However, in several patients, we observed transient monocytosis and granulocytosis which were considered to be suggestive evidence of differentiation of leukemia cells.