In vitro pharmacodynamics of ceftazidime against Pseudomonas aeruginosa isolates from cystic fibrosis patients.

The concentration/MIC (C/MIC) ratio maximizing the bactericidal activity of ceftazidime against 10 Pseudomonas aeruginosa isolates from cystic fibrosis patients was identified. Bactericidal activity was assessed by determining the percent difference in the area under the killing curve at each C/MIC ratio for all of the isolates from that of their growth control. The percent effect at each C/MIC ratio was fitted to a sigmoidal Emax model with maximum bactericidal activity defined as the C/MIC ratio that produced an effect that was 90% of the Emax. Our results suggest that at least some isolates may require higher C/MIC ratios than previously reported for maximal activity.