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A. Empiric Antimicrobial Therapy
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Empiric (or presumptive) 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.
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B. Principles of Antimicrobial Therapy
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Antimicrobial therapy in established infections is guided by several principles.
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1. Susceptibility testing
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The results of susceptibility testing establish the drug sensitivity of the organism. These results usually predict the minimum inhibitory ...