Pathogen-specific Antimicrobial Treatment of Pneumonia
Pathogen	Preferred antimicrobial	Alternative antimicrobial
Streptococcus pneumoniae
Penicillin susceptiblea	Penicillin G; amoxicillin	Cephalosporins (cefazolin, cefuroxime, cefotaxime, ceftriaxone, or cefepime); oral cephalosporins (cefpodoxime, cefprozil, or cefuroxime); imipenem or meropenem; macrolidesb; clindamycin; fluoroquinolone c; doxycycline; ampicillin with or without sulbactam or piperacillin with or without tazobactam
Penicillin-resistantd	Agents based on in vitro susceptibility tests, including cefotaxime and ceftriaxone; fluoroquinolonec; vancomycin
Haemophilus influenzae	Cephalosporin (2d or 3d generation); doxycycline; ß-lactam/ß-lactamase inhibitor; azithromycin; trimethoprim-sulfamethoxazole (TMP-SMZ)	Fluoroquinolone c; clarithromycin
Moraxella catarrhalis	Cephalosporin (2d or 3d generation); trimethoprim-sulfamethoxazole (TMP-SMZ); macrolides; ß-lactam/ß-lactamase inhibitor; clindamycin	Fluoroquinolone c
Anaerobes	ß-lactam/ß-lactamase inhibitor; clindamycin	Imipenem
Staphylococcus aureuse
Methicillin-susceptible	Nafcillin/oxacillin with or without rifampin or gentamicine	Cefazolin or cefuroxime; vancomycin; clindamycin; trimethoprim-sulfamethoxazole (TMP-SMZ)
Methicillin-resistant	Vancomycin with or without rifampin or gentamicin	Linezolid
Enterobacteriaceaef	Cephalosporin (3d generation) with or without aminoglycoside; carbapenem	Aztreonam; ß-lactam/ß-lactamase inhibitor; fluoroquinolonec
Pseudomonas aeruginosae	Aminoglycoside plus antipseudomonal ß-lactam: ticarcillin, piperacillin, mezlocillin, ceftazidime, cefepime, aztreonam, or carbapenem	Aminoglycoside plus ciprofloxacin; ciprofloxacin plus antipseudomonal ß-lactam
Legionella	Macrolideb with or without rifampin; fluoroquinolonec (including ciprofloxacin)	Doxycycline with or without rifampin
Mycoplasma pneumoniae	Doxycycline; macrolideb	Fluoroquinolonec
Chlamydia pneumoniae	Doxycycline; macrolide	Fluoroquinolonec
Chlamydia psittaci	Doxycycline	Erythromycin; chloramphenicol
Nocardia	Trimethoprim-sulfamethoxazole (TMP-SMZ); sulfonamide with or without minocycline or amikacin	Imipenem with or without amikacin; doxycycline or minocycline
Coxiella burnetti (Q fever)	Tetracycline	Chloramphenicol
Influenza virus	Amantadine or rimantadine (influenza A); zanamavir or oseltamivir (influenza A or B)
Hantavirus	Supportive care
a MIC, <2 micrograms/mL. b Erythromycin, clarithromycin, azithromycin, or dirithromycin; Streptococcus pneumoniae, especially strains with reduced susceptibility to penicillin, should have verified in vitro susceptibility. c Levofloxacin, gatifloxacin, moxifloxacin, trovafloxacin, or other fluoroquinolone with enhanced activity against Streptococcus pneumoniae; ciprofloxacin is appropriate for Legionella, Chlamydia pneumoniae, fluoroquinolone-susceptible S. aureus, and most gram-negative bacilli; ciprofloxacin may not be as effective as other quinolones against Streptococcus pneumoniae. d MIC, >2 micrograms/mL. e In vitro susceptibility tests are required for optimal treatment; against Enterobacter species, the preferred antibiotics are fluoroquinolones and carbapenems. f Coliforms: Escherichia coli, Klebsiella, Proteus, and Enterobacter.

Empirical Antibiotics for Community-Acquired Pneumonia

Outpatients Generally preferred are (not in any particular order): doxycycline, a macrolides, or a fluoroquinolone Selection consideration is based on multiple variables, including severity of the illness, the patient’s age, antimicrobial intolerance or side effects, clinical features, comorbidities, concomitant medications, exposures, and epidemiological setting. (These agents have activity against the most likely pathogens in this setting, which include Streptococcus pneumoniae, Mycoplasma pneumoniae, and Chlamydia pneumoniae Selection should be influenced by regional antibiotic susceptibility patterns for Streptococcus pneumoniae and the presence of other risk factors for drug-resistant Streptococcus pneumoniae Penicillin-resistant pneumococci may be resistant to macrolides and/or doxycycline For older patients or those with underlying disease, a fluoroquinolone may be a preferred choice; some authorities prefer to reserve fluoroquinolones for such patients Hospitalized patients General medical ward An extended spectrum cephalosporin combined with a macrolide or a ß-lactam/ß-lactamase inhibitor combined with a macrolide or a fluoroquinolone (alone). Intensive care unit (ICU) pts with serious pneumonia An extended-spectrum cephalosporin or ß-lactam/ß-lactamase inhibitor plus either fluoroquinolone or macrolide. Alternatives or modifying factors: Structural lung disease: antipseudomonal agents (piperacillin, piperacillin-tazobactam, carbapenem, or cefepime) plus a fluoroquinolone (including high-dose ciprofloxacin) ß-lactam allergy: fluoroquinolone with or without clindamycin Suspected aspiration: fluoroquinolone with or without clindamycin, metronidazole, or a ß-lactam/ß-lactamase inhibitor

Definitions: ß-lactam/ß-lactamase inhibitor = ampicillin-sulbactam or piperacillin-tazobactam. Extended-spectrum cephalosporin = cefotaxime or ceftriaxone. Fluoroquinolone = gatifloxacin, levofloxacin, moxifloxacin, or other fluoroquinolone with enhanced activity against Streptococcus pneumoniae (for aspiration pneumonia, some fluoroquinolones show in vitro activity against anaerobic pulmonary pathogens, although there are no clinical studies to verify activity in vivo). Macrolide = azithromycin, clarithromycin, or erythromycin.

Patients who fail to respond: When patients fail to respond or their conditions deteriorate after initiation of empirical therapy, a number of possibilities should be considered . Incorrect diagnosis (not an infection or underlying non-infectious disease with infectious component): noninfectious illnesses that may account for the clinical and radiographic findings include congestive heart failure, pulmonary embolus, atelectasis, sarcoidosis, neoplasms, radiation pneumonitis, pulmonary drug reactions, vasculitis, adult respiratory distress syndrome (ARDS), pulmonary hemorrhage, and inflammatory lung disease. Correct diagnosis: if a correct diagnosis has been made, but the patient fails to respond, the physician should consider each of the following components of the host-drug-pathogen triad: Host-related problems Drug-related problems Pathogen-related problems