Intra-Abdominal Infections

There is a long list of possible intra-abdominal infections:

  • Acute diverticulitis
  • Cholecystitis (with secondary infection)
  • Ascending cholangitis
  • Appendicitis
  • Spontaneous bacterial peritonitis
  • Intra-abdominal abscess


Common Causes of Intra-Abdominal Infections

  • Anaerobes (e.g. bacteroides and clostridium)
  • E. coli
  • Klebsiella
  • Enterococcus
  • Streptococcus


Treating Intra-Abdominal Infections

When treating intra abdominal infections a broad spectrum of antibiotic cover is required unless culture results are available. This is to cover gram positive, gram negative and anaerobic bacteria. Always follow the local guidelines as these are frequently changed based on local resistance and infection control issues.


Antibiotics for Intra-Abdominal Infections


This provides good gram positive, gram negative and anaerobic cover. It does not cover pseudomonas or atypical bacteria.


Ciprofloxacin and levofloxacin provide reasonable gram positive and gram negative cover and also cover atypical bacteria however they don’t cover anaerobes so are usually paired with metronidazole when treating intra-abdominal infections.


This provides exceptional anaerobic cover but does not provide any cover against aerobic bacteria.


This provides very good gram negative cover with some gram positive cover particularly against staphylococcus. It is bactericidal so works to kill the bacteria rather than just slowing it down.


This provides very good gram positive cover including MRSA. It is often combined with gentamicin (to cover gram negatives) and metronidazole (to cover anaerobes) in patients with penicillin allergy.


These provide good broad spectrum cover against gram positive and gram negative bacteria but are not very effective against anaerobes. They are often avoided due to the risk of developing C. difficile infection.

Tazocin and Meropenem

Piperacillin/Tazobactam (Tazocin) and Meropenem are heavy hitting antibiotics that cover gram positive, gram negative and anaerobic bacteria. They don’t cover atypical bacteria or MRSA and tazocin doesn’t cover ESBLs but they cover almost everything else. They are usually reserved for very unwell patients or those not responding to other antibiotics.


Common Regimes

Some common regimes for intra abdominal infection are:

  • Co-amoxiclav alone
  • Amoxicillin plus gentamicin plus metronidazole
  • Ciprofloxacin plus metronidazole (penicillin allergy)
  • Vancomycin plus gentamicin plus metronidazole (penicillin allergy)

Antibiotics can be given orally where an oral version is avaliable, for example in mild diverticulitis, or intravenous in more serious infections.

A stat dose of gentamicin is often added to regimes not including gentamicin if the patient is severely septic to provide initial strong bactericidal gram negative action.


Spontaneous Bacterial Peritonitis

This is a serious infection that typically occurs in patients with liver failure.

  • Piperacillin/Tazobactam (Tazocin) is often first line
  • Cephalosporins such as cefotaxime are also often used
  • Levofloxacin plus metronidazole is an common alternative in penicillin allergy


Last updated March 2019
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