ASPIRATION PNEUMONIA is difficult to diagnose and differentiate from other aspiration syndromes, community-acquired pneumonia, and hospital-acquired pneumonia. Aspiration pneumonia is linked to a higher mortality rate (29.4%) compared to community-acquired pneumonia (11.6%). Choice of antibiotics will depend on where the pneumonia developed (e.g., community, hospital, long-term care facility), risk factors for resistant infections, and the likelihood that anaerobes are involved.
DEFINITION ― Aspiration pneumonia is a lung infection caused by inhalation of pathologically-colonized oropharyngeal or upper GI secretions. Think of aspiration pneumonia as part of the pneumonia spectrum including community- and hospital-acquired pneumonias, rather than its own entity. Large-volume aspiration of oropharyngeal or upper GI secretions leads to aspiration pneumonia. Microaspiration (small-volume aspiration) of oropharyngeal secretions is normal, especially during sleep. However, microaspiration is involved in the pathogenesis of most pneumonias. Risk factors include alcohol use, poor dentition (increases bacterial load, not necessarily risk of aspiration), dysphagia, gastroesophageal reflux, head, neck, and esophageal cancer. Also include chronic obstructive pulmonary disease (COPD), seizures, degenerative neurologic disease (e.g., multiple sclerosis, Parkinson’s disease; dementia) and enteral feeding (especially if associated with impaired gastric motility, poor cough reflex, and altered mental status).
IS ANAEROBIC COVERAGE NEEDED FOR PRESUMED ASPIRATION PNEUMONIA? ― Not usually. There are limited data to guide anaerobic coverage when treating pneumonia. Anaerobes come to mind as culprits in aspiration pneumonia. But more common causes are typical community- or hospital-acquired pneumonia bugs (S. pneumoniae, S. aureus, Pseudomonas, etc). Don't automatically cover anaerobes for pneumonia patients with aspiration risks, such as swallowing disorders or impaired consciousness (see risk factors above). But if these patients ALSO have severe gum disease or poor dentition, consider adding empiric anaerobic coverage. Evidence is limited, but anaerobic content of their aspirated secretions is higher. In this case, adjust the regimen if possible instead of adding an additional antibiotic. For example, most beta-lactam/beta-lactamase inhibitor combinations (e.g., piperacillin/tazobactam), carbapenems (Meropenem), and some fluoroquinolones (e.g., moxifloxacin), already cover many anaerobes.
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NOTE, ceftazidime/avibactam and levofloxacin, should not be used for anaerobic coverage.
In addition, antibiotics used to treat CAP, HAP, or VAP can be changed to an antibiotic that covers typical CAP pathogens and anaerobes. For example, ceftriaxone can be changed to ampicillin/sulbactam or amoxicillin/clavulanate.
If adding an anaerobic antibiotic, lean toward metronidazole NOT clindamycin. Metronidazole has good oral bioavailability (>90%), covers anaerobes from both "above and below the belt", and has a lower risk of C. difficile infections compared to clindamycin. If using metronidazole, be sure to combine with a beta-lactam. Metronidazole lacks coverage of organisms commonly associated with pneumonia, such as gram-positive bacteria (e.g., S. pneumoniae). Clindamycin also has good oral bioavailability (~90%), has a higher risk of C. difficile infections, and only covers gram-positive organisms and anaerobes from "above the belt". Can consider a fluoroquinolone (e.g., moxifloxacin [covers anaerobes], levofloxacin plus metronidazole if covering for anaerobes), in patients with a severe penicillin allergy. Don't automatically add anaerobic coverage if patients aspirate gastric contents with vomiting. Aspiration can lead to chemical pneumonitis, due to inflammation instead of infection. Antibiotic therapy for aspiration pneumonia (Typical Duration of Therapy = 10 Days).
FOR OUTpatient, amoxicillin-clavulanate 875 mg orally twice a day or 2 g twice daily if the patient has comorbidities (e.g., chronic heart, lung, liver, or renal disease, diabetes mellitus, alcoholism, malignancies, asplenia, immunosuppressing conditions or drugs). OR clindamycin 300 mg orally 4 times a day (add second- or third-generation cephalosporin for aerobic coverage if warranted by culture results). FOR INpatient, levofloxacin 750 mg orally or IV twice a day plus metronidazole (500 mg q6-8h IV or orally). Instead metronidazole, clindamycin (600 mg IV q8h or 300 mg orally 4 times a day) or ampicillin-sulbactam 1.5-3 g IV q6h or piperacillin-tazobactam 3.375 g IV q6h. Other options include moxifloxacin 400 mg/day (IV or orally) and imipenem 0.5-1 g IV q6h or meropenem 1g IV q8h.
REFERENCES
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DiBardino DM, Wunderink RG. Aspiration pneumonia: a review of modern trends. J Crit Care. 2015 Feb;30(1):40-8. Available: https://pubmed.ncbi.nlm.nih.gov/25129577