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Antimicrobial Regimen Selection





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.




  • Image not available. An inevitable consequence of exposing microbes to antimicrobials is that some organisms will develop resistance to the antimicrobial.

  • 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.

  • Image not available. Two guiding principles to consider when treating patients with antimicrobials are (a) make the diagnosis and (b) do no harm!

  • Image not available. Only bacteria that cause disease should be targeted with antimicrobial therapy, and colonizing flora should be left intact whenever possible.

  • Image not available. Bacterial cultures should be obtained prior to antimicrobial therapy in patients with a systemic inflammatory response, risk factors for antimicrobial resistance, or infections where diagnosis or antimicrobial susceptibility is uncertain.

  • Image not available. Drug-specific considerations in antimicrobial selection include the spectrum of activity, effects on nontargeted microbial flora, appropriate dose, pharmacokinetic and pharmacodynamic properties, adverse-effect and drug-interaction profile, and cost.

  • Image not available. Empirical therapy should be based on patient- and antimicrobial-specific factors such as the anatomic location of the infection, the likely pathogens associated with the presentation, the potential for adverse effects, and the antimicrobial spectrum of activity.

  • Image not available. Key patient-specific considerations in antimicrobial selection include recent previous antimicrobial exposures, identification of the anatomic location of infection through physical examination and diagnostic imaging, history of drug allergies, organ dysfunction that may affect drug clearance, immunosuppression, pregnancy, and adherence.

  • Image not available. Patient education, de-escalation of antimicrobial therapy based on culture results, monitoring for clinical response and adverse effects, and appropriate duration of therapy are important treatment components.

  • Image not available. Inadequate diagnosis resulting in poor initial antimicrobial selection, poor source control, or the development of a new infection with a resistant organism are relatively common causes of antimicrobial failure.


The discovery of antimicrobials is among the greatest medical achievements of the 20th century. Prior to the antimicrobial era, patients who ...

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