[Impact of initial antibiotic therapy on the course of resistance to fluoroquinolones and aminoglycosides in Gram-negative bacilli isolated from intensive care patients].

Objective: To evaluate the effect of the initial antibiotic therapy associating a betalactam antibiotic (BLA) with either an aminoglycoside (AG) or a fluoroquinolone (FQ) on the development of resistance of gram-negative bacilli in an intensive care unit.

Study Design: Prospective bacteriological surveillance study.

Patients: The study included 51 patients experiencing a second infection with gram-negative organisms, eight days or more after a first infection.

Method: The incidences of bacterial infection and the antimicrobial susceptibility have been assessed.

Results: The first-choice therapy was based either on BLA + AG (51%), or on BLA + FQ in the others (46%). The causative organisms were Enterobacteriaceae (57%) and Pseudomonas aeruginosa (31%). The second infection occurred 23 +/- 11 days after the first. The main organisms involved were Pseudomonas aeruginosa (51%) and Enterobacteriaceae (41%). In the group treated initially with an AG, only the antibiotic susceptibility for amikacin decreased significantly (72 vs 36%, p < 0.05). The latter was the most prescribed antibiotic (56%). In the FQ group, there was a significant decrease of susceptibility for ciprofloxacin, pefloxacin, netilmicin and tobramycin. The decrease was not significant for gentamicin and amikacin.

Conclusions: In intensive care patients, the use of FQ in association with a BLA increases the resistance to AG and FQ. Therefore it seems preferable to administer an AG in association with a BLA. Amikacine should only be prescribed when justified for a given case.