Tissue penetration of antibiotics Does the treatment reach the target site?

For critically ill patients, infections still imply a major challenge for the treating physician. One key factor of successful treatment is sufficient exposure of the employed antimicrobial agent at the site of infection. In most cases, this is the interstitial space of the infected organ or a body cavity; much rarer vital bacteria are located within body cells. Different methods for assessment of tissue pharmacokinetics of antimicrobial agents in the human body are described, including tissue biopsy, bronchoalveolar lavage and microdialysis, and their implication on interpretation of obtained data are discussed. Tissue pharmacokinetics of the hydrophilic beta-lactam meropenem and the lipophilic fluoroquinolone levofloxacin are compared. Differences in pharmacokinetics between plasma and tissue, healthy volunteers and critically ill patients but also between data obtained in the same organ by different methods are discussed. In order to use pharmacokinetic data to optimize the treatment of critically ill patients, critical appraisal of the causative pathogen, the location of the infection, and the source of the used pharmacokinetic data is necessary.