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After hospital acquired pneumonia is diagnosed, it is imperative that antimicrobial therapy begin promptly because delays in administration of antibiotics have been associated with worse outcomes.3 One study in support of this notion reported a mortality of 30% in patients who received early, appropriate therapy compared with a rate of 91% among patients who did not.11 The initial selection of an antimicrobial agent is almost always made on an empiric basis and is based on factors such as severity of infection, patient-specific risk factors, and total number of days in hospital before onset.
All empiric treatment regimens should include coverage for a group of core organisms that includes aerobic gram negative bacilli (Enterobacter spp, Escherichia coli, Klebsiella spp, Proteus spp, Serratia marcescens, and Hemophilus influenzae) and gram-positive organisms such as Streptococcus pneumoniae and Staphylococcus aureus.
In patients with mild or moderate infections and no specific risk factors for resistant or unusual pathogens, monotherapy with a second-generation cephalosporin such as cefuroxime; a nonpseudomonal third-generation cephalosporin such as ceftriaxone; or a beta-lactam/beta-lactamase inhibitor such as ampicillin/sulbactam, ticarcillin/clavulanate, or piperacillin/tazobactam may be appropriate. For patients in this low-risk category who have an allergy to penicillin, it is appropriate to initially use a fluoroquinolone or clindamycin and aztreonam.While it is acceptable to use a fluoroquinolone in the empiric regimen of patients with penicillin allergies, one recent paper studied the use of penicillin skin testing in these patients and found that most patients with a history of penicillin allergy can safely be treated with penicillin antibiotics, so penicillin skin testing may be a means by which the use of fluoroquinolones can be decreased.
Patients with mild or moderate infections with specific risk factors should have broadened empiric coverage. In patients with witnessed aspiration or in those who have had recent thoracoabdomial surgery, it may be advisable to cover anaerobes by adding clindamycin, although use of a beta-lactam alone may be sufficient. Patients with coma, head trauma, recent infections with influenza virus, diabetes, or chronic renal failure, or who are injection drug users, are at risk for infections by Staphylococcus aureus and may require the addition of vancomycin to cover methicillin-resistant strains until sensitivities are known. Patients who have received long courses of steroids should have a macrolide as a part of their initial therapy, given their increased risk for Legionella spp.
Regardless of the severity of the infection, patients who have received antibiotics previous to developing pneumonia, patients with structural lung disease, patients who have received steroids, and patients with a prolonged ICU course (more than 5 days) should receive a combination of antibiotics to cover not only core pathogens but also infection from Acinetobacter spp or Pseudomonas aeruginosa. Combination therapy should be employed in these cases because of the high rate of acquired resistance among these organisms. Appropriate combinations for this group of patients include an aminoglycoside or ciprofloxacin in addition to a beta-lactam with antipseudomonal coverage. Additionally, vancomycin should be considered if the patient has risk factors that suggest methicillin-resistant Staphylococcus aureus could be a pathogen.
A pneumonia is defined as severe if there is need for admission to an ICU, radiographic evidence of rapid progression, need for mechanical ventilation or high levels of inspired oxygen, or evidence of sepsis. Patients with severe pneumonias who have been hospitalized for less than 5 days but who have no specific risk factors should receive empiric coverage aimed at the core group of organisms only; however, monotherapy is probably not appropriate in these patients and combination therapy should be used. Any patient with a severe pneumonia and any risk factor, including a hospitalization of more than 5 days, should again receive a combination of antibiotics that cover infections by Acinetobacter spp and P aeruginosa.
There is no consensus regarding the duration of antibiotic treatment for all patients with hospital acquired pneumonia, although if the initial clinical suspicion was low, antibiotics may be safely discontinued after 72 hours if the clinical picture has not changed significantly.13 Recommendations from the American Thoracic Society suggested that duration of treatment should be guided by severity, time to clinical response, and the pathogenic organism1; however, a recent panel of experts suggested that "the main factor for deciding the duration of therapy should be the time to clinical response and not the pathogen involved" and that patients should be treated for at least 72 hours after a clinical response is achieved.
Clinical response to antimicrobial therapy is not likely in the first 48 to 72 hours, so the empiric antibiotic regiment should not be changed during this time unless as directed by the results of microbiologic investigation.1 In patients who fail to respond after this initial period, recommendations are that antibiotic coverage should be broadened, noninfectious causes considered, and invasive diagnostic testing performed. Appropriate diagnostic testing may include bronchoscopy with PSB and BAL, radiographic tests to evaluate for the possibility of pleural effusions or abscesses that limit response, or CTs of the sinuses to evaluate for sinusitis, as this may be a cause of persistent symptoms. After excluding all other etiologies in the nonresponding patient, it may be advisable to perform open-lung biopsy for diagnostic purposes, even though this technique has not been shown to improve outcomes
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