Postantibiotic effects of eleven antimicrobials on five bacteria.

AIM: To investigate the postantibiotic effects (PAE) of different classes of antimicrobials against five different types of bacteria.

METHODS

Minimal inhibitory concentrations (MIC) were determined by twofold macrodilution in broth. The antimicrobial agents were eliminated by washing method after the bacteria were exposed to antimicrobials for 1 h or 2 h. Growth curves were followed by viable counts, and then the PAE were calculated.

RESULTS

Macrolides induced PAE of 3.10 h to 4.15 h on S aureus, and 1.85 h to 3.3 h against S pneumoniae, which were longer than PAE induced by other tested antimicrobials (P<0.01). Macrolides induced PAE of 1 h to 4 h against H influenzae, with azithromycin producing the longest PAE of 4 h. Ciprofloxacin and amikacin induced PAE of 1.38 h to 2.00 h on E coli and K pneumoniae, which were longer than that of beta-lactams, piperacillin, cefazolin, or cefotaxime, with PAE of 0.1 h to 0.5 h (P<0.01).

CONCLUSION

Different classes of antimicrobials induce different periods of PAE. As an important pharmacodynamic parameter, PAE provide reference data for the determination of the optimal dosing regimen and reasonable use of antimicrobials.