Patients that are eligible to participate in this study will be those who are receiving intensive cancer treatment for leukemia or those undergoing HSCT.`
eligible participants will be randomly assigned to one of two study arms:
* arm a: no Levofloxacin (standard arm)
* arm B: Levofloxacin (experimental arm)
Patients in arm B will be given levofloxacin by mouth (by vein, if unable to take by mouth) during the period in which they are at the highest risk for serious bacterial infections. Specifically, they will receive levofloxacin daily beginning on the first day of chemotherapy treatment for patients being treated with chemotherapy or 2 days prior to stem cell infusion for stem cell transplant patients. The levofloxacin will be stopped once a participants neutrophil count is higher than 200. The levofloxacin may be stopped and re-started later if participant needs antibiotics for treatment of a new suspected or proven infection.
Participants will also be asked to participate in an optional biological study to learn more about bacteria that are resistant to antibiotics in stool. Participants, who give consent, will be asked to provide peri-rectal swabs (placing a sterile swab in the rectum for five seconds) or stool specimens (collecting a sample of feces following a bowel movement). The samples will be collected three times from participants receiving intensive chemotherapy and two times from participants undergoing stem cell transplant.
-- Patient must be >= 6 months to <= 21 years of age at enrollment.
-- Patient must fit 1 of the following 2 categories (a or b): (a) Chemotherapy patients planned to receive at least 2 consecutive cycles (not required to be the first 2 cycles) of intensive chemotherapy for either 1) de novo, relapsed or secondary AML, or 2) relapsed ALL.
(b) Stem cell transplantation patients Planned to receive at least 1 myeloablative autologous or allogeneic HSCT.
-- Adequate renal function
-- Patients must have a performance status corresponding to ECOG scores of 0, 1, or 2. Use Karnofsky for patients >16 years of age and Lansky for patients <= 16 years of age.