Susceptibility Testing of Pseudomonas aeruginosa Isolates and Clinical Response to Parenteral Antibiotic Administration.

Study objective: To determine the relationship between the antibiotic susceptibility of Pseudomonas aeruginosa isolated from the sputum of patients with cystic fibrosis (CF) and the patient's response to parenteral antibiotic administration, we performed a retrospective analysis using data from patients in the placebo arm of a phase 3 trial of tobramycin solution for inhalation. All patients were chronically infected with P aeruginosa. Seventy-seven of the 262 patients receiving placebo experienced a pulmonary exacerbation during the trial for which they received therapy with IV tobramycin and ceftazidime. The susceptibility of the P aeruginosa isolates to ceftazidime and tobramycin was determined at trial enrollment by broth microdilution. Design: The clinical response to combination antibiotic therapy was assessed by analyzing differences in spirometry before and after antibiotic administration. The FEV[sub 1] percent predicted at the first visit after the conclusion of antibiotic administration was compared to the FEV[sub 1] percent predicted prior to antibiotic therapy. The results were analyzed both descriptively and by regression analyses. Results: The conditions of 54 patients improved, and those of 9 patients worsened, and in 14 patients there was no change in FEV[sub 1] with antibiotic administration. No correlation was observed between the susceptibility of P aeruginosa to tobramycin or ceftazidime and clinical response. Only the three following variables were observed to significantly correlate with FEV[sub 1] after antibiotic treatment on regression analysis: FEV[sub 1] prior to treatment (p < 0.0001); number of days elapsed between the previous FEV[sub 1] measurement and the initiation of IV antibiotic therapy (p < 0.002); and the number of days elapsed between the determination of the minimum inhibitory concentration and the initiation of IV therapy (p < 0.03). No significant trends were observed between the antibiotic susceptibility of P... [ABSTRACT FROM AUTHOR]