Phase I and II study of fludarabine phosphate in leukemia: therapeutic efficacy with delayed central nervous system toxicity.

Fludarabine phosphate (9-beta-D-arabinofuranosyl-2-fluoroadenine), a novel purine nucleoside, has demonstrated excellent preclinical antitumor activity and little toxicity in phase I clinical trials. We evaluated the clinical use of fludarabine given as a continuous intravenous (IV) infusion for remission induction in patients with relapsed or refractory leukemia. Thirty infusions were administered to 25 patients. At doses less than or equal to 125 mg/m2/d for five days, only three of 17 patients cleared their bone marrow of leukemic cells, and none achieved complete remission (CR). Nine patients received doses of 150 mg/m2/d for five days or 125 mg/m2/d for seven days. Four of these patients achieved CR (three patients with acute nonlymphoblastic leukemia (ANLL), one patient with acute lymphoblastic leukemia (ALL]. However, severe CNS toxicity was encountered in five patients at the two highest dose levels. Initial symptoms of neurotoxicity were delayed from 21 to 43 days after starting treatment and consisted of optic neuritis, cortical blindness, altered mental status, and generalized seizure. Only one patient regained visual and neurologic function; four other patients experienced progressive neurologic deterioration and died. Clinicopathologic evaluation suggested widespread, severe demyelination as the etiology of these reactions. We conclude that fludarabine is an effective drug for remission induction in acute leukemia. However, doses required to achieve CR are associated with unacceptable CNS toxicity. In view of its potent antileukemic activity, further evaluation of fludarabine at lower doses (less than or equal to 75 mg/m2/d for five days) may be warranted in combination with other chemotherapeutic agents for the treatment of patients with acute leukemia.