The pharmacokinetic profile of quinolones compared with other antimicrobial agents

Despite a high degree of absorption and relatively low fraction of plasma-protein binding, the quinolone derivatives yield substantially lower serum concentrations on a dose-size basis than do either the aminoglycoside or beta-lactam-type antimicrobials. This is a result of their rapid and extensive cell penetration. This concentrating of drug within cells requires that dose size and frequency be carefully programmed to maintain blood and extracellular fluid levels of the quinoloness that are above the minimum inhibitory concentrations for extracellular pathogens. However, it may provide an advantage against intracellular pathogens such as Legionella and Chlamydia. A further advantage of the quinolones is that they undergo renal excretion, hepatic metabolism, and transintestinal elimination via the gastrointestinal tract. Because one of the pathways may compensate when another is defective, the half-lives of the quinolones may not rise precipitously even when renal function declines.