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Antibiotics are the foundation of therapy for respiratory tract infections. This approach varies with the type of pneumonia, age of the affected patient, presence of various comorbid illnesses and risk factors for infection by specific pathogens, and the severity of the acute illness. For most of the patients, initial therapy is empiric, aimed at a broad spectrum of potential pathogens (see Chapter 122). Once culture data become available, therapy can be pathogen-specific making it possible to de-escalate to fewer drugs with a narrower antimicrobial spectrum.1,2 In some cases, initial empiric therapy must be continued because no etiologic pathogen is identified (see Chapter 123).

When a pathogen is defined, the term “appropriate” refers to the use of at least one antimicrobial agent that is active in vitro against the etiologic pathogen.1 The term “adequate” includes not only appropriate therapy, but also the use of that agent in the correct dose, via the right route, given in a timely fashion, and with penetration to the site of infection. Timely and appropriate antibiotic therapy can improve survival in patients with community-acquired pneumonia (CAP) and nosocomial pneumonia or hospital-acquired pneumonia (HAP) and the benefits are most evident in patients who are not otherwise terminally ill.1,35 In general, with severe illness, those receiving antibiotics earlier in their course have a lower mortality than those receiving delayed therapy, with the risk of death rising 7% to 8% for each hour of delay of therapy during the first 6 hours of septic shock and hypotension.6

The term HAP encompasses pneumonia in nonventilated patients, ventilated patients, and those with healthcare-associated pneumonia (HCAP) (see Chapter 129). Ventilator-associated pneumonia (VAP) is nosocomial pneumonia that develops after at least 48 hours of preceding mechanical ventilation, and thus some ventilated HAP patients may not have VAP, since they do not satisfy this definition of prolonged preceding mechanical ventilation. HCAP includes those coming from nursing homes, those in the hospital for more than 2 days in the past 90 days, those with a history of regular visits to places like dialysis or infusion centers, or those getting home wound care. Because of their exposure to the healthcare environment, some patients with HCAP are at risk for infection with multidrug-resistant (MDR) pathogens, although not all of these patients are at the same risk. Presence of this entity has blurred the distinction between CAP and HAP, since HCAP patients may reside in the “community,” but be infected with organisms very similar to those present in patients with HAP.

In the setting of CAP, effective initial antibiotic therapy is associated with a marked improvement in survival, compared to ineffective therapy, particularly in patients with severe illness.3,7 In several studies, identification of the pathogens causing severe CAP did not lead to an improved survival rate, while the use of a broad-spectrum, empiric regimen ...

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