Effects of antibiotic exposure following allo-HCT with non-myeloablative Flu-TBI conditioning

This was a single-center retrospective analysis that included patients who received allo-HCT following fludarabine/higher total body irradiation (Flu-TBI) -based NMA conditioning for a hematologic malignancy. 

Flu-TBI conditioning consisted of 30 mg/m2 fludarabine on Days −4, −3, and −2, and low-dose TBI on Day −1. 

In the event of mismatched unrelated donor transplant, patients received additional in vivo T cell depletion with 2 mg/kg/day rabbit-ATG on Days −8, −7, −6, and −5.  

Antibiotics received by patients included ciprofloxacin, ceftazidime, meropenem, ceftazidime, metronidazole, and valacyclovir. 

Key outcome measures included non-relapse mortality (NRM), relapse-free survival (RFS), OS, and GvHD relapse-free survival (GRFS). 

A total of 150 patients were included that had received Flu-TBI-based NMA conditioning. 

Median patient age was 59 years and 53% were male.  

Antibiotic exposure occurred in 60% of patients, with 40% receiving prophylactic ciprofloxacin, and 20% receiving broad-spectrum antibiotics.  

NRM at 1 year was 19% in patients who received antibiotics, and 10% in those who did not.  

OS and RFS were not significantly affected by antibiotic exposure. 

GRFS was significantly lower in patients receiving antibiotics vs those who did not (42% vs 55%). 

Antibiotic exposure was shown to play a significant role in the occurrence of GvHD (Figure 1).