Pharmacodynamics of antimicrobial therapy in surgery

INTRODUCTION: ''Pharmacodynamics'' refers to the relationship of drug concentrations in serum or tissues to effects on biologic systems, Concepts used to describe antimicrobial pharmacodynamics include the minimal inhibitory concentration (MIG), the minimal bactericidal concentration (MBC), and serum bactericidal titers (SET), as well as post-antibiotic effect. METHODS: Pertinent published literature was identified through a MEDLINE search. RESULTS: Aminoglycosides have a concentration-dependent effect on bacteria killing and possess a relatively long postantibiotic effect. Given these characteristics, single-daily dosing, where the total daily dose with a traditional aminoglycoside regimen is given as one dose, may be more efficacious compared with more frequent dosing. For beta-lactam antimicrobials, bacterial killing is related to the duration of time that the free drug concentration exceeds the bacterial MIG. Beta-lactam antimicrobials have been shown to have no, or a short postantibiotic effect, Beta-lactam antimicrobials may be more effective when administered as continuous intravenous infusions. CONCLUSIONS: Pharmacodynamic variation may result from differences in drug sensitivity among individuals and the nature of the interaction between antimicrobials and microorganisms. Proper use of pharmacokinetic and pharmacodynamic principles can result in more effective and less toxic antimicrobial regimens.