Levofloxacin in Preventing Infection in Young Patients With Acute Leukemia Receiving Chemotherapy or Undergoing Stem Cell Transplantation

Inclusion Criteria: * Patient must fit 1 of the following 2 categories: * Chemotherapy patients * Planned to receive at least 2 consecutive cycles (not required to be the first 2 cycles) of intensive chemotherapy for either: * De novo, relapsed or secondary acute myeloid leukemia (AML), or acute leukemia of ambiguous lineage treated with standard AML therapy * Relapsed acute lymphoblastic leukemia (ALL) * For the purposes of this study, "intensive chemotherapy" is defined as regimens that are predicted by the local investigator to cause neutropenia for \> 7 days; examples include, but are not limited to, treatment with "4-drug induction" (anthracycline, vincristine, asparaginase, and steroid), high dose cytarabine, anthracycline/cytarabine, ifosfamide/etoposide, and clofarabine-containing regimens * Stem cell transplantation patients * Planned to receive at least 1 myeloablative autologous or allogeneic HSCT * For the purposes of this study, myeloablative autologous and allogeneic HSCT are those in which the conditioning regimen is predicted by the local Investigator to cause neutropenia for \> 7 days * Creatinine clearance or radioisotope glomerular filtration rate (GFR) \> 70 mL/min/1.73 m\^2 OR serum creatinine based on age/gender as follows: * 0.5 mg/dL (6 months to \< 1 year of age) * 0.6 mg/dL (1 to \< 2 years of age) * 0.8 mg/dL (2 to \< 6 years of age) * 1.0 mg/dL (6 to \< 10 years of age) * 1.2 mg/dL (10 to \< 13 year…