SHOULD PSEUDOMONAS-AERUGINOSA ISOLATES RESISTANT TO ONE OF THE FLUORINATED QUINOLONES BE TESTED FOR THE OTHERS - STUDIES WITH AN EXPERIMENTAL-MODEL OF PNEUMONIA

A clinical isolate of Pseudomonas aenuginosa resistant to pefloxacin ( Pef) but susceptible to ciprofloxacin (Cip) was studied to compare the in vitro and in vivo activities of Pef, ofloxacin (Off), and Cip, The time-kill curve method showed no bactericidal activity for Pef and Of l, but a reduction of 4 log(10) CFU/ml was achieved with Cip at 1 h, A model of experimental P. aeruginosa pneumonia was used to evaluate in vivo the relevance of the difference in susceptibility observed in vi tro, At 36 h, a 100% cumulative survival rate was observed in Cip-trea ted rats, which was far higher than the survival rate obtained with Pe f (53%) or Ofl (46%) (P < 0.001), At 4 h, no bacteremia was observed i n Cip-treated rats, whereas 93% of the Pef-treated rats and 80% of the OA-treated rats were bacteremic (P < 0.001), The best pulmonary bacte rial clearance was observed with Cip, Interestingly, Pef and Ofl, to w hich the strain was resistant in vitro, showed a fairly good in vivo a ctivity despite sub-MIG concentrations, Cip was more effective than Pe f and Ofl in terms of pulmonary and systemic bactericidal activity and provided the best survival rate in animals, We conclude that differen ces between the different quinolones in terms of the organism's sensit ivity assessed in vitro may be relevant and that it might be useful to reconsider the use of a quinolone to which P. aeruginosa shows resist ance if the organism shows sensitivity to no other agent.