Intra-Abdominal Infection

Intra-Abdominal Infection is a topic covered in the Washington Manual of Medical Therapeutics.

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  • Intra-abdominal infections occur because of inflammation or disruption of the gastrointestinal tract and can be classified as low risk (uncomplicated) or high risk (complicated).
  • Infections are typically polymicrobial with enteric gram-negative bacilli (e.g., E. coli, Klebsiella spp.), Enterococcus spp., and especially anaerobes such as Bacteroides fragilis.
  • Low-risk community–acquired infection includes acute diverticulitis, colitis, or appendiceal abscess. These can be treated with a β-lactam/β-lactamase inhibitor combination, ertapenem, or a third-generation cephalosporin (e.g., ceftriaxone) plus metronidazole.
  • High-risk community infections are severe infections and occur in patients at risk for adverse outcomes or resistant pathogens (e.g., age >70 years, comorbidities, immunocompromise, delay in source control). An agent with activity against P. aeruginosa and resistant Enterobacteriaceae such as meropenem, imipenem, or piperacillin-tazobactam, or a combination of cefepime with metronidazole can be used.
  • Health care-associated infections (HAIs) may be caused by MDRO and require additional antibiotics if ESBL-producing organisms or MRSA are a consideration.
  • Source control with abscess drainage or surgical resection is critical.
  • Avoid clindamycin, cefoxitin, and moxifloxacin owing to high rates of resistance among B. fragilis.
  • Empiric antifungal coverage is usually not indicated unless yeast is grown from a sterile site.1 See Table 14-8.
    Table 14-8: Empiric Therapy Examples for Intra-Abdominal Infections
    Oral Regimens
    • Ciprofloxacin 500–750 mg PO q12h +  metronidazole 500 mg PO q8h
    • Moxifloxacin 400 mg PO qday
    Parenteral Regimens
    Low risk—no concern for Pseudomonas aeruginosa
    • Ertapenem 1 g IV q24h
    • Ceftriaxone 1–2 g IV qday + metronidazole 500 mg IV q8h
    • Piperacillin/tazobactam 4.5 g IV q6h
    High risk—concern for P. aeruginosa
    • Piperacillin/tazobactam 4.5 g IV q6h
    • Cefepime 1–2 g IV q8h + metronidazole 500 mg IV q8h
    • Ciprofloxacin 400 mg IV q8–12h + metronidazole 500 mg IV q8h
    • Meropenem 1 g IV q8h or imipenem-cilastin 500 mg IV q6h
    Concern for vancomycin-resistant Enterococcus spp.a
    • Add linezolid 600 mg PO/IV q12h or daptomycin 6–8 mg/kg IV qday to above regimens
    Concern for yeasta
    • Add echinocandin (e.g., micafungin 100 mg IV qday) or fluconazole 400 mg PO/IV qday to above regimens

    aIf isolated from a sterile site.

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