ABSTRACT
Cytarabine is intracellularly activated and correlations have been established between the pharmacokinetic behaviour of active metabolites and their antileukemic effect. Recently, a good response to high-dose treatment of leukemias has additionally been attributed to a so-called low deamination phenotype of cytarabine inactivation. Consequently, these findings would support plasma level monitoring of cytarabine and its metabolite uracil arabinoside in high-dose cytarabine regimens. This pharmacokinetic study presents data attempting to reevaluate these observations. Thirty-seven patients were treated by 3-h high-dose cytarabine infusions (9 patients 1000 mg/m2, 28 patients 3000 mg/m2) as part of their treatment for acute leukemia. Serial blood samples during and post infusion were analysed for cytarabine (araC) and its deamination product uracil arabinoside (araU) using HPLC with UV-detection. Considerable interindividual variation was observed in end-infusion plasma concentrations of araC (1000 mg/m2: 2.1-fold, 3000 mg/m2: 5.5-fold) and araU (1000 mg/m2: 2.7-fold, 3000 mg/m2: 2.9-fold). The median ratio of end infusion concentrations araU/araC (on a molar basis) was 5.6 (S.D. 3.0), extreme ratio values were 2 and 14. No differences of the araU/araC ratio were found between the two dosages used. Minimum plasma araC concentrations at the end of infusion were 10.5 micromol/l and 22.0 micromol/l at a dose of 1000 and 3000 mg/m2, respectively. In our European study population a "fast" deamination phenotype of cytarabine (araU/araC ratio > 14) was not be observed.
Subject(s)
Antimetabolites, Antineoplastic/pharmacokinetics , Arabinofuranosyluracil/pharmacokinetics , Cytarabine/pharmacokinetics , Leukemia/drug therapy , Myelodysplastic Syndromes/drug therapy , Acute Disease , Adult , Aged , Antimetabolites, Antineoplastic/administration & dosage , Arabinofuranosyluracil/administration & dosage , Cytarabine/administration & dosage , Deamination , Dose-Response Relationship, Drug , Female , Humans , Male , Middle AgedABSTRACT
An ion-pair high pressure liquid chromatographic method is described for the determination of cytarabine (CAS 147-94-4, araC) in human plasma. Complete separation is achieved within 10 min using a reversed stationary phase and an isocratic eluent containing 0.4 mmol/l heptane sulfonic acid as modifier. Detection by UV-absorption occurs at 270 nm. Quantification of cytarabine and of its main plasma metabolite uracil arabinoside (araU) is achieved by means of internal standardisation using adenine arabinoside (araA). Retention times of araU, araC, and araA are 3.9, 5.9 and 9.4 min, respectively. Detection limits of araC and araU are 10 and 15 ng/ml, resp. During a pharmacokinetic study of high-dose cytarabine treatment no interferences could be observed in plasma samples.
