Empiric antimicrobial therapy

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. 

Many areas of the human body are colonized with bacteria— this is known as normal flora. Infections often arise from one s own normal flora (also called an endogenous infection). Endogenous infection may occur when there are alterations in the normal flora (e.g., recent antimicrobial use may allow for overgrowth of other normal flora) or disruption of host defenses (e.g., a break or entry in the skin). Knowing what organisms reside where can help to guide empirical antimicrobial therapy (Fig. 66-1). In addition, it is beneficial to know what anatomic sites are normally sterile. These include the cerebrospinal fluid, blood, and urine. 

The patient was admitted to the hospital with a presumptive diagnosis of health care-associated pneumonia (based on the recent hospitalization). He received intravenous hydration with normal saline, 5 L oxygen via face mask, an insulin infusion to control his glucose, and empirical antimicrobial therapy with piperacillin-tazobactam 2.25 g intravenously every 6 hours and vancomycin 1 g intravenously every 24 hours. All other medications are continued with the exception of the diabetes medications. 

Empirical antimicrobial therapy should be modified on the basis of laboratory data and clinical response. 

Determine if the patient can undergo an immediate LP or if the LP should be delayed until a CNS mass lesion can be ruled out. If the LP is delayed, blood cultures should be drawn and appropriate empirical antimicrobial therapy initiated immediately. 

The severity of a patient s infection, based on the PEDIS scale, guides the selection of empirical antimicrobial therapy. While most patients with grade 2 diabetic foot infections can be treated as outpatients with oral antimicrobial agents, all grade 4 and many grade 3 infections require hospitalization, stabilization of the patient, and broad-spectrum IV antibiotic therapy.31... 

Empiric antimicrobial therapy should target likely causative pathogen(s) based on patient-specific risk factors and route of infection. However, therapy should be modified based on culture and sensitivity data. 

Empiric antimicrobial therapy Antimicrobial therapy given prior to the availability of microbiologic culture results. 

Adachi JA, Ostrosky-Zeichner L, DuPont HL, Ericsson CD Empirical antimicrobial therapy for traveler s diarrhea. Clin Infect Dis 2000 31 1079-1083. 

Empiric antimicrobial therapy should be instituted as soon as possible to eradicate the causative organism (Table 36-2). Antimicrobial therapy should last at least 48 to 72 hours or until the diagnosis of bacterial meningitis can be ruled out. Continued therapy should be based on the assessment of clinical improvement, cultures, and susceptibility testing results. Once a pathogen is identified, antibiotic therapy should be tailored to the specific pathogen. 

TABLE 43-6 1 Empirical Antimicrobial Therapy for Pneumonia in Adults ... 

Selection of empiric antimicrobial therapy should be based on the most likely organisms. The most common organisms for acute exacerbation of COPD are Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, and H. parainfluenzae. 

Antimicrobial agents are frequently used before the pathogen responsible for a particular illness or the susceptibility to a particular antimicrobial agent is known. This use of antimicrobial agents is called empiric (or presumptive) therapy and is based on experience with a particular clinical entity. The usual justification for empiric therapy is the hope that early intervention will improve the outcome in the best cases, this has been established by placebo-controlled, double-blind prospective clinical trials. For example, treatment of febrile episodes in neutropenic cancer patients with empiric antimicrobial therapy has been demonstrated to have impressive morbidity and mortality benefits even though the specific bacterial agent responsible for fever is determined for only a minority of such episodes. 

Table 51-1 Empiric Antimicrobial Therapy Based on Microbiologic Etiology. ...

These extended case studies complement the basic information presented in Chapters 1 to 40. They reinforce basic principles of pharmacology, such as the role of patient factors in empiric antimicrobial therapy Most of the cases provide clinical information obtained from a single patient some cases describe a composite of typical features derived from several patients. These cases illustrate simple pharmacologic principles, such as consideration of kidney function in drug dosing—concepts useful in answering examination questions, and in the clinics. 

Initial selection of antimicrobial therapy is nearly always empirical, which is the initiation of antimicrobials sometimes prior to documentation of the presence of infection and before the offending organism is identified. Infectious diseases generally are acute, and a delay in antimicrobial therapy may result in serious morbidity or even mortality. An example is the rapidly lethal nature of various forms of meningitis. Thus empirical antimicrobial therapy selection is... 

After initiation of empirical antimicrobial therapy, judicious assessment of febrile neutropenic cancer patients is mandatory to evaluate response, clinical status, laboratory data, and potential need for therapy adjustments. After the administration of 72 hours or more of empirical antimicrobial therapy, the clinical status and culture results of febrile neutropenic patients should be reevaluated to determine whether or not therapeutic modifications are necessary. Additions or modifications to the initial antimicrobial regimen likely will be required in patients with ANCs of fewer than 500 cells/mm for greater than a week. Modifications of antimicrobial therapy should be based on clinical and laboratory data antibiotic therapy should be optimized based on culture results. However, during periods of neutropenia, patients generally should continue to receive broad-spectrum therapy because of the risk of secondary infections or breakthrough bacteremias when antimicrobial coverage is too narrow. ... 

A key controversy in the management of febrile neutropenia in cancer patients is the optimal time to stop empirical antimicrobial therapy in patients who remain persistently febrile. Patients individual risk of severe infection (determined by extent and duration of neutropenia, as well as other risk factors) helps to guide treatment decisions in this setting. 

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