Plasma Concentration of Cytosine Arabinoside (Ara-C) in the Eldery 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.; 10mg/m2/12hr, 14-21 days), continuous drip infusion of Ara-C (Ara-C d. i. V.; 20mg/m2/day, 24hr 14 days) and/or oral administration of cytarabine ocfosfate (SPAC) (SPAC p. o.; 100mg-300mg/body/day, 14 days) by radioimmunoassay. In the Ara-C s. c. patients, the peak plasma level (Cmax) of Ara-C was 103ng/ml and the time to reach Cmax was 15min. The elimination half-like (t1/2) was 25min 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 3-8ng/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 0.32ng/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 4-7ng/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.