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INTRODUCTION

A. Empiric Antimicrobial Therapy

Empiric antimicrobial therapy is begun before a specific pathogen has been identified and is based on the presumption of an infection that requires immediate drug treatment. Before initiation of such therapy, accepted practice involves making a clinical diagnosis of microbial infection, obtaining specimens for laboratory analyses, making a microbiologic diagnosis, deciding whether treatment should precede the results of laboratory tests, and, finally, selecting the optimal drug or drugs. A variety of publications and the internet provide updated lists of antimicrobial drugs of choice for specific pathogens. Such lists can provide a useful guide to empiric therapy based on presumptive microbiologic diagnosis. Tables 51–1 and 51–2 show examples of empiric antimicrobial therapy based on microbiologic etiology.

TABLE 51–1Examples of empiric antimicrobial therapy based on microbiologic etiology.a
TABLE 51–2Further examples of empiric antimicrobial therapy based on microbiologic etiology.a
B. Principles of Antimicrobial Therapy

Antimicrobial therapy in established infections is guided by several principles.

1. Susceptibility testing

The results of susceptibility testing establish the drug sensitivity of the organism. These results usually predict the minimum inhibitory concentrations (MICs) of a drug for comparison ...

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