Impact of a fluoroquinolone formulary change on acquisition of quinolone-resistant gram-negative bacilli

Rising rates of fluoroquinolone resistance in bacteria have been associated with increased fluoroquinolone use. In vitro data show differences in potency among fluoroquinolone antibiotics against gram-negative bacteria and have led to the hypothesis that rates of selection of resistant microorganisms may be affected by the choice of the specific fluoroquinolone. Because clinical data to prove this hypothesis are lacking, the aim of the present study was to determine rates of acquisition of quinolone-resistant gram-negative bacilli (QRGNB) in the fecal flora of medical intensive care unit patients before and after a formulary change from ciprofloxacin to levofloxacin. Unadjusted rate ratios for acquisition of QRGNB were 1.09 (95%CI, 1.02-1.16) for each day of ciprofloxacin use and 1.01 (95%CI, 0.87-1.17) for each day of levofloxacin use. Following adjustment for other antibiotic use, enteral feeding, APACHE II score, and nursing home admission, neither ciprofloxacin nor levofloxacin use was associated with acquisition of QRGNB. In conclusion, a formulary change from ciprofloxacin to levofloxacin was not significantly associated with an increased risk of acquisition of QRGNB.