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For further information, see CMDT Part 33-31: Anaerobic Infections

Key Features

  • Frequently occur in the setting of poor oral hygiene and periodontal disease, aspiration of saliva (which contains 108 anaerobic organisms per milliliter in addition to aerobes)

  • May lead to necrotizing pneumonia, lung abscess, and empyema

  • Polymicrobial infection is the rule

  • Anaerobes are frequently isolated etiologic agents, particularly

    • Prevotella melaninogenica

    • Fusobacteria

    • Peptostreptococci

Clinical Findings

  • Fever

  • Productive cough

  • Night sweats

  • Weight loss

  • Chronic course of illness

  • Poor dentition (frequently)


  • Pleural fluid culture

  • Chest radiograph

  • CT scan


  • Clindamycin, 600 mg intravenously once, followed by 300 mg every 6–8 hours orally, is the treatment of choice

  • Metronidazole is an alternative

    • But does not cover facultative streptococci, which are often present

    • So, if used, a second agent active against streptococci, such as ceftriaxone, 1 g/day intravenously or intramuscularly should be added

  • Penicillin, 2 million units every 4 hours intravenously, followed by amoxicillin, 750–1000 mg every 12 hours orally, is an alternative, although increasing prevalence of β-lactamase–producing organisms is common

  • Moxifloxacin, 400 mg once daily orally or intravenously may be used

  • Because these infections respond slowly, a prolonged course of therapy (eg, 4–6 weeks) is generally recommended

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