HIGHLY SENSITIVE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ASSAY FOR 1-BETA-D-ARABINOFURANOSYLCYTOSINE-5'-STEARYL PHOSPHATE (CYTARABINE-OCFOSFATE)

An ion-pair HPLC method for the determination of 1-beta-D-arabinofuran osylcytosine-5'-stearyl phosphate (cytarabine-ocfosfate I) was develop ed, using a phenyl-bonded column under reversed-phase conditions with a mobile phase of acetonitrile-buffered water (pH 6.8) (50:50) for iso cratic elution. A reproducible sample clean-up was achieved by solid-p hase extraction. In order to reach the low limit of detection of 2 ng/ ml, an enrichment switching system was used. The present validation le ads to a limit of quantification of 5 ng/ml with a coefficient of vari ation (C.V.) of 10%. The total time of measurement was shortened by a back-flush procedure to restore the conditions after each run. UV dete ction at 275 nm was applied. The recoveries for plasma samples ranged from 56.4 to 64.1%, regardless of drug concentrations. The intra-assay C.V. was about 4% (40 measurements at four different concentrations). The inter-assay recovery (ten measurements over ten days) at a plasma concentration of 50 ng/ml was 57% with a C.V. of 8.25%. Based on this HPLC method, the pharmacokinetics of I were measured during a clinica l phase I/II study.