Once-a-day cephalosporins: reality or myth?

The factors that may influence the pharmacodynamics of antimicrobial agents against microorganisms at the site of infection must be considered before using once-daily antimicrobial chemotherapy in clinical practice. From a pharmacokinetic point of view, we can establish which antibiotic is suitable for once-daily therapy. For aminoglycosides and quinolones, where the bacterial killing is rapid and dose dependent, and there is a post-antibiotic effect (PAE), the pharmacodynamic objective is to maintain the tissue levels way above the minimum inhibitory concentration (MIC) for a short period. This can be achieved by giving single bolus doses at long time intervals. With beta-lactam antibiotics, however, which have a slow time-dependent antibacterial effect and do not display a PAE, the aim is to keep the antibiotic concentration above the MIC for the duration of therapy.