Application of Pharmacokinetics and Pharmacodynamics to Antibiotic Selection

Choosing the best antimicrobial agent for a particular patient or infection can be a complicated process. Ideally, the best drug can be determined by comparing the properties of individual agents with each other. A favorable clinical profile (i.e., excellent efficacy, few adverse effects) is clearly the most important variable used for selection. However, this can be difficult when newer agents are being compared with older, established ones. Newer agents can show equivalent or superior clinical efficacy, yet their safety might not be established until they have been on the market for a couple of years or more. In one study, half of all warnings by the U.S. Food and Drug Administration (FDA) were issued within seven years of a drug’s introduction to the market, and half of the drug withdrawals from the market occurred within two years of their introduction.1 The true efficacy and safety of a drug can be established only with extensive use. It is difficult to choose an antibiotic from a group of two or more comparators because each drug within a class is likely to possess some favorable features. Few trials have directly compared the clinical efficacy of two drugs within a class, and studies that do so are usually underpowered and designed only to show equivalence. Generally, other drug characteristics must be used as means of comparison, for example: