Variables predicting response to high dose cytosine arabinoside therapy in patients with refractory acute leukemia.

The cytotoxic effect of cytosine arabinoside (ara-C) is presumably mediated by cytosine arabinoside 5'-triphosphate (ara-CTP). We tested for a correlation between intracellular ara-CTP pharmacokinetics and clinical response among 51 patients who received high dose ara-C (3 g/m2 at 12-hr intervals) as therapy for refractory acute leukemia. After accounting for pretreatment clinical variables that correlated with response, measurement of ara-CTP pharmacokinetics added significant prognostic information. This provides a rationale for manipulation of schedules of high dose ara-C administration in those patients whose pharmacokinetic characteristics are inconsistent with response to an every 12-hr schedule.