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Complicated Intra-Abdominal Infection

Abdominal/Pelvic

Source: IDMP View on spectrum chart →
Patient + scenario modifiers
Patient
Clinical scenario / source

Annotations only — chart still shows the full chemistry of each drug.

1. Clinical Syndrome

Infection extending beyond a hollow viscus into the peritoneum or a confined abscess: secondary peritonitis (perforated viscus), perforated appendix or diverticulum, acute cholangitis, post-op intra-abdominal abscess, gangrenous cholecystitis.

Excludes: uncomplicated appendicitis / diverticulitis without perforation (often briefer, narrower regimen), spontaneous bacterial peritonitis (different epidemiology — separate syndrome), C. difficile colitis (use clostridioides-difficile-infection), uncomplicated cholecystitis without sepsis (often surgical alone).

2. Pathogens

Consider the patient: Healthcare exposure (recent admission, recent abx → MDRO risk), immunocompromise (broader empirics + Candida risk), prior abdominal surgery (post-op leak risk), liver disease.

Consider the case: Source identifiable on imaging? Source control achievable (drainage, surgery)? Severity (sepsis, septic shock). Upper-GI perforation + recent broad abx + septic shock → empiric antifungal.

Common

Less common

3. Empiric Therapy

TierFirst choiceAlternativesDurationComments
Outpatient — with comorbidities
  • 875 mg · PO BID · PO · 4–7 days post source control
  • 500 mg · PO BID · PO · 4–7 days
  • 500 mg · PO TID · PO · 4–7 days

    Combine with cipro — single agent FQ has no anaerobe coverage.

4–7 days post source control (STOP-IT trial)Mild, source-controlled disease (e.g., uncomplicated diverticulitis post drainage).
Admitted to ward
  • 2 g · q24h · IV · 4–7 days post source control
  • 500 mg · q8h · IV · 4–7 days
  • 1 g · q24h · IV

    Single-agent (covers anaerobes); good for OPAT.

  • 3 g · q6h · IV

    If enterococcus coverage desired in mild disease (rising B. fragilis resistance limits use for severe disease).

4 days post source control (STOP-IT trial)Community-acquired moderate cIAI without sepsis. Source control first (drain, OR).
Admitted to ICU
  • 4.5 g · q6h (extended infusion) · IV · 7 days post source control
  • 1 g · q8h · IV

    If ESBL risk or healthcare-associated.

7 days post source controlSevere / healthcare-associated cIAI. Add fluconazole or echinocandin if Candida risk (upper-GI perforation, recent broad abx, septic shock).
ICU — Pseudomonas risk
  • 1 g · q8h · IV
  • load + AUC-guided · — · IV

    Add if MRSA risk or healthcare-associated severe disease.

  • Fluconazole 400–800 mg load then 400 mg · daily · IV/PO

    Add if Candida risk factors. Echinocandin (caspofungin/micafungin) if azole-resistant or critically ill.

7+ days post source controlSeptic shock with healthcare exposure. Discuss with ID + surgery.

Add coverage if:

MRSA coverage
  • Known MRSA colonization
  • Severe healthcare-associated disease
  • Persistent positive cultures

Add:

  • load + AUC-guided · — · IV
Pseudomonas coverage
  • Healthcare-associated infection
  • Recent broad-spectrum antibiotics ≤90 days
  • Immunocompromise

Add:

  • 4.5 g · q6h · IV

    Or meropenem, cefepime. Replaces ceftriaxone.

ESBL coverage
  • Prior ESBL isolate
  • Broad-spectrum antibiotic exposure ≤90 days
  • Severe disease

Add:

  • 1 g · q8h · IV

    Or ertapenem if not septic.

VRE coverage
  • Prior VRE isolate
  • Liver transplant recipient
  • Prolonged hospitalization with broad-spectrum coverage

Add:

  • 600 mg · q12h · IV/PO

4. Directed Therapy

Source control is the priority — drainage (percutaneous, surgical), source removal, anastomotic revision. Antibiotics alone fail without source control.

Once cultures back: narrow to most active narrow agent. For mild community-acquired cIAI, don't routinely treat enterococcus from peritoneal cultures unless severe disease, valvular heart disease, or healthcare-associated.

STOP-IT trial: 4 days post-source-control = equivalent outcomes to 8+ days for adequately drained disease. For healthcare-associated severe cIAI, 7 days reasonable. Persistent fever or rising WBC at 48–72 h → re-image for retained source.

5. Monitoring

Resolution: fever curve, WBC trend, lactate, abdominal exam. Re-image at 48–72 h if not improving.

Toxicity: vanco AUC + Cr; metronidazole prolonged → neuropathy; cefepime mental status; pip-tazo + vanco AKI risk.

Pearls

Source control beats antibiotics. STOP-IT trial: 4 days post drainage is enough for most cIAI. Don't routinely cover Candida in community-acquired cIAI — risk-stratify: upper-GI perforation, recent broad abx, septic shock, immunocompromise, recurrent leakage. Empiric Enterococcus coverage controversial — favor only for severe / healthcare-associated.

References