Anaerobic Infections, Intra-Abdominal

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

Key Features

Each gram of stool contains up to 10¹¹ anaerobes, predominantly
- Bacteroides fragilis
- Clostridia
- Peptostreptococci
These organisms play a central role in most intra-abdominal abscesses
- Diverticulitis
- Appendicitis
- Perirectal abscess
They may also participate in hepatic abscess and 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

Examination, laboratory tests, cultures, and CT scan

Treatment

Therapy should be directed both against anaerobes and gram-negative aerobes
Antibiotics that are reliably active against B fragilis include
- Metronidazole
- Moxifloxacin
- Tigecycline
- Chloramphenicol
- Carbapenems (ertapenem, imipenem, doripenem)
- Ampicillin-sulbactam
- Ticarcillin-clavulanic acid
- Piperacillin-tazobactam
Table 33–6 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 33–6.Treatment of anaerobic intra-abdominal infections.

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Table 33–6. 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

Ceftriaxone 1 g intravenously every 24 hours plus metronidazole intravenously or orally, 500 mg 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 6–8 hours or meropenem 1 g every 8 hours or doripenem 0.5 g every 8 hours or piperacillin/tazobactam 3.75 g every 6 hours

Health care–associated

Intravenous therapy

Imipenem 0.5 g intravenously every 6–8 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

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

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