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Anaerobic Infections, Intra-Abdominal

For further information, see CMDT Part 35-31: Anaerobic Infections

KEY FEATURES

  • Anaerobes—predominantly B fragilis, Clostridia, and peptostreptococci – make up more than 90% of colonic bacteria

  • These organisms play a central role in most intra-abdominal abscesses after trauma to the colon and in

    • Diverticulitis

    • Appendicitis

    • Perirectal abscess

    • Hepatic abscess

    • Cholecystitis

  • The bacteriology of these infections includes anaerobes as well as enteric gram-negative rods and, on occasion, enterococci

CLINICAL FINDINGS

  • Related to infected organ

DIAGNOSIS

  • Physical examination, laboratory tests, cultures, and CT scan

TREATMENT

  • Therapy for intra-abdominal infections should be directed against both anaerobes and gram-negative aerobes

  • Antibiotics that are reliably active against B fragilis include

    • Metronidazole

    • Chloramphenicol

    • Moxifloxacin

    • Tigecycline

    • Carbapenems (ertapenem, imipenem, meropenem)

    • Ampicillin-sulbactam

    • Ticarcillin-clavulanic acid

    • Piperacillin-tazobactam

  • Resistance to cefoxitin, cefotetan, and clindamycin is increasingly encountered

  • Table 35–3 summarizes the antibiotic regimens for management of

    • Moderate to moderately severe infections (eg, patient hemodynamically stable, good surgical drainage possible or established, low APACHE score, no multiple-organ failure)

    • Severe infections (eg, major peritoneal soilage, large or multiple abscesses, patient hemodynamically unstable), particularly if drug-resistant organisms are suspected

Table 35–3.Treatment of anaerobic intra-abdominal infections.
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Table 35–3. Treatment of anaerobic intra-abdominal infections.

Community-onset

 Oral therapy

  Moxifloxacin, 400 mg every 24 hours

  Ciprofloxacin, 750 mg twice a day, or levofloxacin, 750 mg once a day, plus metronidazole, 500 mg every 8 hours

 Intravenous therapy

  Moderate to moderately severe infections:

  Ertapenem, 1 g intravenously every 24 hours

  or

  Ceftriaxone, 1 g intravenously every 24 hours, plus metronidazole, 500 mg intravenously or orally every 8 hours. If penicillin-allergic, can replace ceftriaxone with ciprofloxacin, 400 mg intravenously (or 500 mg orally) every 12 hours

  Severe infections:

  Imipenem, 0.5 g intravenously every 6 hours (or 1 g intravenously every 8 hours), or meropenem, 1 g every 8 hours or doripenem, 0.5 g every 8 hours or piperacillin/tazobactam, 3.375 g every 6 hours (non-pseudomonal dosing)1

Health care–associated

 Intravenous therapy

  Imipenem, 0.5 g intravenously every 6 hours (or 1 g intravenously every 8 hours), or meropenem, 1 g every 8 hours, or doripenem, 0.5 g every 8 hours, or piperacillin/tazobactam, 4.5 g every 6 hours (pseudomonal dosing)1

  or

  Ceftazidime or cefepime, 2 g intravenously every 8 hours, plus metronidazole, 500 mg intravenously or orally every 8 hours

1For both pseudomonal and non-pseudomonal infections, piperacillin/tazobactam can also be given via extended infusion dosing, wherein the antibiotic is given as a one-time 4.5 g intravenous loading dose infused over 30 minutes, followed by 4.5 g intravenously infused over 4 hours every 8 hours (starting 4 hours after the loading dose).

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