Ciprofloxacin and levofloxacin are both in guidelines to use for prophylaxis in autologous and allogeneic Stem cell transplant.Ciprofloxacin was recently replaced by levofloxacin as the preferred agent in some transplant centers. In some small retrospective studies ciprofloxacin prophylaxis was associated with a higher rate of breakthrough gram positive bloodstream infections. However, the optimum oral agent for antibacterial prophylaxis in transplant recipients remains uncertain.

Inclusion Criteria:

• Patients 18-75 years of age with a diagnosis of a hematological malignancy. Meet the stem cell transplant program criteria to undergo autologous or allogeneic hematopoietic stem cell transplantation.

Exclusion Criteria:

• Prolonged QT
• Allergies to ciprofloxacin or levofloxacin

2 months

Our study has several limitations that need to be considered when interpreting the results. First, the study was randomized but open-label. This could have influenced decisions about patient care, potentially biasing the results. Second, the study only documented infections until day 60, which might not capture resistant bacterial infections that may occur later. Third, this study unfortunately lacks information on the gut microbiome, which might play a role in the observed outcomes.