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Upon completion of the chapter, the reader will be able to:

  1. Recognize that antimicrobial resistance is an inevitable consequence of antimicrobial therapy.

  2. Describe how antimicrobials differ from other drug classes in terms of their effects on individual patients as well as on society as a whole.

  3. Identify two guiding principles to consider when treating patients with antimicrobials, and apply these principles in patient care.

  4. Differentiate between microbial colonization and infection based on patient history, physical examination, and laboratory and culture results.

  5. Evaluate and apply at least six major drug-specific considerations when selecting antimicrobial therapy.

  6. Evaluate and apply at least seven major patient-specific considerations when selecting antimicrobial therapy.

  7. Select empirical antimicrobial therapy based on spectrum-of-activity considerations that provide a measured response proportional to the severity of illness. Provide a rationale for why a measured response in antimicrobial selection is appropriate.

  8. Identify and apply five major principles of patient education and monitoring response to antimicrobial therapy.

  9. Identify two common causes of patients failing to improve while on antimicrobials, and recognize other less common but potential reasons for antimicrobial failure.


Since 1980, infectious disease–related mortality in the United States has increased, in part owing to increases in antimicrobial resistance. The discovery of virtually every new class of antimicrobials has occurred in response to the development of bacterial resistance and loss of clinical effectiveness of existing antimicrobials. KEY CONCEPT An inevitable consequence of exposing microbes to antimicrobials is that some organisms will develop resistance to the antimicrobial. Today, there are many antimicrobial classes and antimicrobials available for clinical use. However, in many cases, differences in mechanisms of action between antimicrobials are minor, and the microbiologic properties of the agents are similar. KEY CONCEPT Antimicrobials are different from other classes of pharmaceuticals because they exert their action on bacteria infecting the host as opposed to acting directly on the host. Because antimicrobial use in one patient affects not only that patient but also other patients if they become infected with resistant bacteria, correct selection, use, and monitoring of clinical response are paramount.

KEY CONCEPT There are two guiding principles to consider when treating patients with antimicrobials: (a) make the correct diagnosis and (b) do no harm! Patients with infections frequently present with signs and symptoms that are nonspecific and may be confused with other noninfectious disease. Not only is it important to determine whether a disease process is of infectious origin, but it is also important to determine the specific causative pathogen of the infection. Antimicrobials vary in their spectrum of activity, the ability to inhibit or kill different species of bacteria. Antimicrobials that kill many different species of bacteria are called broad-spectrum antimicrobials, whereas antimicrobials that kill only a few species of bacteria are called narrow-spectrum antimicrobials. One might argue that treating everybody with broad spectrum antimicrobials will increase the likelihood that a patient will ...

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