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PRINCIPLES OF ANTIMICROBIAL THERAPY
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The discovery and rapid development of targeted antimicrobial agents, beginning in the 1930s, are among the most important scientific developments of 20th-century medicine. These drugs have changed the practice of medicine and remain one of medicine’s most effective and widely used interventions. However, choosing an appropriate antimicrobial can be complex and difficult. Optimal antimicrobial use requires appreciation of the complicated interactions between host, organism, and drug. This decision-making process, summarized in Table 39–1, begins with an accurate working diagnosis, based on the patient’s clinical history, physical examination, exposure history, and initial laboratory tests. From this foundation, the clinician must consider the most likely organism(s) and that organism’s likely pattern of antimicrobial susceptibility. This information is considered in the context of numerous patient-specific factors, including age, immune status, relevant comorbidities, site of infection, prior antimicrobial exposure, the microbiology of the patient’s prior infections, and the pace and severity of the illness. Unique exposures, based on environment, travel, diet, animal contact, or ill close contacts may suggest the likelihood of certain organisms. However, decisions of when not to use antimicrobials are equally important, as unnecessary or additional drugs and longer durations may harm patients. In addition to choosing an appropriate antimicrobial for treatment of a suspected or confirmed infection, antimicrobials are also often utilized to prevent infections (preexposure prophylaxis, post-exposure prophylaxis, or surgical/medical prophylaxis) and the same appreciation of the complicated interactions between host, organism, and drug should be utilized in these situations.
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Once an appropriate initial antimicrobial is chosen, the clinician must consider the proper dose, route of administration, duration of therapy, and whether additional drugs are needed. Empiric therapy should be changed ...