[Plasma concentration of cytosine arabinoside (Ara-C) in the elderly patients with hematological malignancy treated by Ara-C or cytarabine ocfosfate (SPAC)].

Plasma concentration of cytosine arabinoside (Ara-C) was determined in elderly patients with myelodysplastic syndromes or acute myelocytic leukemia who were treated with subcutaneous injection of Ara-C (Ara-C s.c.; 10 mg/m2/12 hr, 14-21 days), continuous drip infusion of Ara-C (Ara-C d.i.v.; 20 mg/m2/day, 24 hr 14 days) and/or oral administration of cytarabine ocfosfate (SPAC) (SPAC p.o.; 100 mg-300 mg/body/day, 14 days) by radioimmunoassay. In the Ara-C s.c. patients, the peak plasma level (Cmax) of Ara-C was 103 ng/ml and the time to reach Cmax was 15 min. The elimination half-like (t1/2) was 25 min and no accumulation was detected after 14 days of consecutive Ara-C s.c. administrations. In the SPAC p.o. patients, Cmax of Ara-C was 3-8 ng/ml and it took 3-5 days to reach Cmax. The plasma concentration level of Ara-C remains almost at the Cmax level during the SPAC p.o. administration and it remained higher than 0.32 ng/ml for as long as 15 days after the end of administration. In a Ara-C d.i.v. patient, plasma level of Ara-C was detected 4-7 ng/ml during the administration (day 7 through day 14). In all patients bone marrow suppression was observed after chemotherapy regardless of regimen, and there was no significant difference between nadir peripheral cell blood counts of Ara-C s.c. patients and SPAC p.o. patients.