The pharmacology of antimicrobial therapy can be divided into two distinct components (figure 1). The first of these components is pharmacokinetics, or the absorption, distribution, and elimination of drugs. These factors, combined with the dosage regimen, determine the time course of drug concentra-tions in serum, which in turn determine the time course of drug concentrations in tissues and body fluids. With respect to antimicrobials, the time course of drug concentrations at the site of infection is of special interest. Pharmacodynamics is the relationship between serum concentration and the pharmacological and toxicological effects of drugs. With respect to antimicrobials, the primary interest is in the relationship between concentration and the antimicrobial effect. The time course of antimicrobial activity is a reflection of the interrelationship between pharmacokinetics and pharmacodynamics. Studies over the past 20 years have demonstrated marked differences in the time course of antimicrobial activity among antibacterials [1-3]. Furthermore, the pattern of antimicrobial activity over time is an important determinant of effective dosage regimens [4]. This review will focus on the interrelationship between pharmacokinetics and pharmacodynamics in determining dosing regimens for different classes of antibacterials. The ability of specific pharmacokinetic/pharmacodynamic parameters to predict the efficacy of antibacterial activity in animal models of infection and in human infections will be emphasized.

Pharmacodynamics: Parameters of Antimicrobial Activity