Intra-abdominal infection: Antibiotics

• Abdominal infections are usually polymicrobial and result in an intra-abdominal abscess or secondary peritonitis, which may be generalized or localized (phlegmon).
• predominant bacteria involved in such infections are coliforms (mainly Escherichia coli, Klebsiella spp, Proteus spp, and Enterobacter spp) streptococci, enterococci, and anaerobic bacteria
• dominant isolates in most series are Bacteroides fragilis and E. coli

Choice of antibiotics

• although clindamycin and cefotetan were previously considered acceptable options for intra-abdominal infections involving anaerobes, these drugs are no longer recommended due to escalating rates of resistance in the B. fragilis group.
• As detailed in those guidelines, ampicillin-sulbactam is also not recommended due to high rates of resistance among community-acquired E. coli
• Single-drug regimens that have expanded activity against gram-negative aerobic and anaerobic bacilli include meropenem, imipenem-cilastatin, doripenem, and piperacillin-tazobactam. Combination regimens include ceftazidime or cefepime in combination with metronidazole.
• Cephalosporin-based regimens lack anti-enterococcal activity, so ampicillin or vancomycin can be added to these regimens for enterococcal coverage until culture results are available.
• For those known to be colonized with ampicillin-resistant, vancomycin-resistant Enterococcus (VRE), a VRE-active agent, such as linezolid or daptomycin, should be included
• comparable in vitro efficacy of cefoperazone-sulbactam and piperacillin-tazobactam

Empiric antibiotic regimens for low-risk community-acquired intra-abdominal infections

	Dose
Single-agent regimen
Ertapenem	1 g IV once daily
Piperacillin-tazobactam	3.375 g IV every six hours
Ticarcillin-clavulanate	3.1 g IV every four hours
Combination regimen with metronidazole
Cefazolin	1-2 g IV every eight hours
OR
Cefuroxime	1.5 g IV every eight hours
OR
Ceftriaxone	1 g IV once daily
OR
Cefotaxime	1-2 g IV every six hours
OR
Ciprofloxacin	400 mg IV every twelve hours or 500 mg PO every twelve hours
OR
Levofloxacin	750 mg IV or PO once daily
PLUS
Metronidazole	500 mg IV or PO every eight hours

Empiric antibiotic regimens for high-risk community-acquired intra-abdominal infections

	Dose
Single-agent regimen
Imipenem-cilastatin	500 mg IV every six hours
Meropenem	1 g IV every eight hours
Doripenem	500 mg IV every eight hours
Piperacillin-tazobactam	4.5 g IV every six hours
Combination regimen with metronidazole
Cefepime	2 g IV every eight hours
OR
Ceftazidime	2 g IV every eight hours
OR
Ciprofloxacin	400 mg IV every twelve hours
OR
Levofloxacin	750 mg IV once daily
PLUS
Metronidazole	500 mg IV every eight hours

Empiric antibiotic regimens for healthcare-associated intra-abdominal infections

	Dose
Single-agent regimen
Imipenem-cilastatin	500 mg IV every six hours
Meropenem	1 g IV every eight hours
Doripenem	500 mg IV every eight hours
Piperacillin-tazobactam	4.5 g IV every six hours
Combination regimen
Cefepime	2 g IV every eight hours
OR
Ceftazidime	2 g IV every eight hours
PLUS
Metronidazole	500 mg IV every eight hours
PLUS
Ampicillin*	2 g IV every six hours
OR
Vancomycin*	15-20 mg/kg IV every eight to twelve hours

References:

1. www.uptodate.com
2. Cefobid product leaflet
3. Comparison of in vitro activities of ceftazidime, piperacillin-tazobactam, and cefoperazone-sulbactam, and the implication on empirical therapy in patients with cancer. Indian J Cancer 2009;46:318-22
4. http://www.antimicrobe.org/drugpopup/Cefoperazone.htm
5. Updated Guideline on Diagnosis and Treatment of Intra-abdominal Infections. Am Fam Physician. 2010 Sep 15;82(6):694-709. 
6. Diagnosis and Management of Complicated Intra-abdominal Infection in Adults and Children: Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America. Clin Infect Dis. (2010) 50 (2): 133-164. 
7. https://www.ncbi.nlm.nih.gov/pubmed/18570578 
8. Canadian practice guidelines for surgical intra-abdominal infections. Can J Infect Dis Med Microbiol. 2010 Spring; 21(1): 11–37.