A Phase I Study of Idarubicin Dose Escalation for Remission Induction Therapy in Acute Myeloid Leukemia

The maximum tolerated dose (MTD) of idarubicin has been acknowledged to be 12-15 mg/m²/day for 3 days for acute leukemias. Its MTD should be reevaluated in the treatment of acute myeloid leukemia (AML) in the era of granulocyte colony-stimulating factor and better supportive care. We conducted a phase I study to investigate the safety of escalating doses of idarubicin in combination with cytarabine 100 mg/m²/day for 7 days for previously untreated AML. The starting dose of idarubicin was 12 mg/m²/day for 3 days with dose escalations by 3 mg/m²/day. Cohorts of three patients were treated at each dose level, and the idarubicin dose was escalated up to 18 mg/m²/day until at least two patients among a cohort of three to six patients experienced the dose-limiting toxicities (DLTs) (traditional 3+3 design for phase I clinical trials: J Natl Cancer Inst 2009;101:708). Hematologic DLTs were defined as the time to recovery of neutrophils {absolute neutrophil count (ANC) ≥500/μL} or platelets (platelet count ≥20,000/μL) exceeded 42 days after the start of induction therapy (J Clin Oncol 2004;22:4290). Non-hematologic DLTs were defined as grade 4 or 5 toxicities (Leukemia 1998;12:865). We adopted the NCI CTCAE v3.0 to grade the hematologic and non-hematologic toxicities. Thirteen adult patients were enrolled in the study, but two and two were excluded at level 1 and level 2, respectively, because they received reinduction therapy for resistant disease within 4 weeks after the start of the assigned induction therapy. Consequently, nine patients were evaluable for the phase I study. The median times to recovery of neutrophils (ANC ≥500/μL) after the start of induction therapy at level 1, level 2, and level 3 were day 20 (range, 19-22), day 19 (range, 17-20), and day 25 (range, 21-26), respectively. The median times to recovery of platelet (platelet count ≥20,000/μL) at each level were day 20 (range, 19-23), day 20 (range, 16-34), and day 24 (range, 20-35), respectively. Therefore, grade 4 hematologic toxicities were observed at all 3 levels; however, these hematologic toxicities did not meet the criteria of the hematologic DLTs as defined in this study. There was any instance of grade 4 non-hematologic toxicity at each dose level. No death associated with the induction treatment was observed in this trial. Hematologic and non-hematologic DLTs as defined above were not observed at all 3 dose levels; therefore, idarubicin 18 mg/m²/day for 3 days could be defined as the MTD for this trial.