Patients admitted to the ICU have severe pneumonia, and the likely etiology includes S. pneumoniae, H. influenzae as in the other categories; however, the incidence of L. pneumophila increases in this setting and should be included in the organism differential. In addition, enteric gram-negative bacilli and S. aureus are more frequently the cause of the pneumonia. The recommendations are to treat with an IV ft-lactam plus either azithromycin or a respiratory fluoroquinolone. This combination therapy minimizes the risk of treatment failure due to a resistant pathogen as well as provides coverage against all of the potential pathogens.28 The preferred ft-lactams are ceftriaxone, cefotaxime, or ampicillin-sulbactam. If the patient is allergic to ft-lactams then aztreo-nam plus a respiratory fluoroquinolone are preferred.
If P. aeruginosa is suspected (e.g., patient comes from a long-term care facility, or recent hospitalization) then the antimicrobial treatment must be broadened to cover Pseudomonas as well as the organisms listed above. Owing to the high resistance rates observed in Pseudomonas, the recommended regimens empirically double cover the Pseudomonas to ensure at least one of the antibiotics is active against Pseudomonas. The regimens include the use of an antipneumococcal, antipseudomonal ft-lactam (cefepime, ceftazidime, piperacillin/tazobactam, imipenem, or meropenem) plus either ciprofloxacin or levofloxacin or an aminoglycoside. If the aminoglycoside is chosen, then either IV azithromycin or a respiratory fluoroquinolone should be ad-
ded to cover S. pneumoniae and the atypical bacterial organisms.
If CA-MRSA is suspected in the patient then the addition of vancomycin or linezolid to the above regimen should be considered. Daptomycin cannot be used because surfactant in the lung inactivates the drug thus rendering it ineffective for pneumonia. CA-MRSA can cause a necrotizing pneumonia, and the cause is believed to be due to the increased pathogenicity of this strain and its multiple toxins including the Panton-Valentine leukocidin toxin.9 In these patients the use of an agent which decreases toxin production may be beneficial. Linezolid does decrease toxin production and the agents recommended to be added to vancomycin therapy are clindamycin or a respiratory fluoroquinolone.28
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