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Antimicrobial Regimen Selection

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

  10. Define antimicrobial stewardship and describe the purpose of such a program.


The CDC’s Antibiotic Resistance Threats in the United States 2013 estimates more than 2 million patients per year are infected with resistant pathogens resulting in approximately 23,000 deaths.1 For several decades, 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. Image not available. 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. Image not available. 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.

Image not available. 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 diseases. 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. ...

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