To better comprehend the antibiotic recommendations in this article, the reader should be cognizant of a number of clinical, microbiologic, pharmacologic, and epidemiologic observations, as well as fundamental pharmacodynamic concepts. Taking into consideration that empiric antimicrobial therapy in the critical care unit (CCU) is the norm rather than the exception, the clinician must be familiar with the suspected pathogens from infectious processes acquired both in the community and in the hospital. In fact, most often the actual causative pathogen(s) of a given infection is rarely determined with certainty. A fundamental understanding of pharmacodynamic concepts is essential; it forms the very basis for the design of dosing strategies that maximize clinical efficacy while minimizing toxicity.