Principles of antibiotic usage.

New antibiotics must demonstrate an advantage over older agents with respect to therapeutic efficacy, protection against infection, toxicity, cost, and pharmacokinetic properties before they can be approved for public consumption. In order to use antibiotics properly, we must know more about whether certain organisms are resistant or sensitive to the drug; it must also be determined how sensitive or resistant the bacterium is to the drug and how long serum and tissue levels remain above inhibitory or bactericidal concentrations of the drug for the suspected or proven pathogen. Cost issues and potential for adverse reactions must also be considered. In brief, to prevent or treat infections the clinician must be familiar with the microbiology, pharmacology, toxicology, and cost of antibiotics.