The pharmacodynamic and pharmacokinetic properties of antibiotics have received increased attention in recent years, leading to optimization of dosage regimens. In view of these characteristics, certain fluoroquinolones may prove advantageous compared with other antimicrobials for treatment of selected infections. Several new fluoroquinolone antimicrobial agents have potency equal to or greater than that of beta-lactam antibiotics against gram-negative aerobic bacilli, including Pseudomonas aeruginosa. In vitro bactericidal activity of these compounds is more rapid than that of the beta-lactams, often resembling that for the aminoglycosides. Like the aminoglycosides, but in contrast to the beta-lactams, fluoroquinolones exert a significant in vitro postantibiotic effect against some strains of P. aeruginosa and Enterobacteriaceae. However, unlike many beta-lactam and aminoglycoside antimicrobial agents that have similar in vitro activity, fluoroquinolones are often effective both after oral and parenteral administration. Important pharmacokinetic properties of fluoroquinolones include differences in the extent and variability in oral absorption and clearance, which determine the extent of in vivo exposure to drug. Drugs and dosage regimens that result in a high degree of exposure, particularly high peak levels of drug, may be preferable because of a greater extent of bacterial killing and less selection of drug-resistant bacteria.