Pharmacodynamics of antimicrobial agents. Bactericidal and postantibiotic effects.

Pharmacodynamics of an antimicrobial agent relate the time course of concentrations of the drug to the antimicrobial effects at the site of infection. Antimicrobial agents can be divided into three main groups, based on antimicrobial pharmacodynamic characteristics: 1) agents that exhibit concentration-dependent bactericidal activity over a wide range of drug concentrations (e.g., the aminoglycosides and fluoroquinolones); 2) agents that exhibit time-dependent bactericidal activity that has little relationship to the magnitude of the drug concentrations, as long as the concentrations are above a minimally effective level (e.g., vancomycin and beta- lactam antibiotics); and 3) agents that exhibit predominantly a bacteriostatic effect. Knowledge of the antimicrobial pharmacodynamic characteristics provides a more rational basis for determination of optimal dosing regimens in terms of size of the dose and length of the dosing interval.