Against the background of reduced susceptibility of many pathogens to available antibacterial agents an optimized dosing of antibiotics is of increasing importance to avoid therapeutic failures and / or microbial resistance. Consideration of the individual body weight, as well as kidney and liver function of a patient and the pharmacodynamics and pharmacokinetic properties of the antibiotic should enable an individualized dosing. An optimized approach could increase efficacy and safety of an antimicrobial therapy significantly. Aimed studies in overweight patients during the clinical development of a new antibiotic are necessary as a substantial prerequisite for a pharmacokinetically based optimized dosing. Intensive care patients also exhibit major changes in pharmacokinetics of antibiotics due to pathophysiological changes. An increased volume of distribution, an increased clearance and reduced protein binding require treatment with increased doses. On the other hand, in patients with acute renal failure often doses have to be reduced and / or the dosing interval has to be prolonged. Renal function should be assessed on the basis of the creatinine clearance. An estimation with the often applied plasma creatinine-based equations can lead to wrong results in critically ill patients, a directly measured urinary creatinine clearance is a more reasonable procedure. However, so far only few prospective studies which investigated the effect of alternative dosing strategies on the therapeutic outcome have been published. Certainly, further comprehensive studies are necessary.