When Should a Patient with Ascites Receive Spontaneous Bacterial Peritonitis (SBP) Prophylaxis?

Colored-enhanced CT scan of an axial section through the abdomen showing ascites.

Case

A 54-year-old man with end-stage liver disease (ESLD) and no prior history of spontaneous bacterial peritonitis (SBP) presents with increasing shortness of breath and abdominal distention. He is admitted for worsening volume overload. The patient reveals that he has not been compliant with his diuretics. On the day of admission, a large-volume paracentesis is performed. Results are significant for a white blood cell count of 150 cells/mm3 and a total protein of 0.9 g/ul. The patient is started on furosemide and spironolactone, and his symptoms significantly improve throughout his hospitalization. His medications are reconciled on the day of discharge. He is not on any antibiotics for SBP prophylaxis; should he be? In general, which patients with ascites should receive SBP prophylaxis?

Overview

Spontaneous bacterial peritonitis is an infection of ascitic fluid that occurs in the absence of an indentified intra-abdominal source of infection or inflammation, i.e., perforation or abscess.¹ It is diagnosed when the polymorphonuclear cell (PMN) count in the ascitic fluid is equal to or greater than 250 cells/mm3, with or without positive cultures.

SBP is a significant cause of morbidity and mortality in patients with cirrhosis, with the mortality rate approaching 20% to 40%.2 Of the 32% to 34% of cirrhotic patients who present with, or develop, a bacterial infection during their hospitalization, 25% are due to SBP.¹ Changes in gut motility, mucosal defense, and microflora allow for translocation of bacteria into enteric lymph nodes and the bloodstream, resulting in seeding of the peritoneal fluid and SBP.¹ Alterations in both systemic and localized immune defenses, both of which are reduced in patients with liver disease, also play a role in SBP pathogenesis (see Table 1, p. 41).

Current evidence supports the use of a third-generation cephalosporin or amoxicillin/clavulanate for initial treatment of SBP, as most infections are caused by gram-negative bacilli, in particular E. coli (see Table 2 on p. 41 and Table 3 on p. 42).1 Alternatively, an oral or intravenous fluoroquinolone could be used if the prevalence of fluoroquinolone-resistant organisms is low.¹

Due to the frequency and morbidity associated with SBP, there is great interest in preventing it. However, the use of prophylactic antibiotics needs to be restricted to patients who are at highest risk of developing SBP. According to numerous studies, patients at high risk for SBP include:

1. Patients with a prior SBP history;
2. Patients admitted with a gastrointestinal bleed; and
3. Patients with low total protein content in their ascitic fluid (defined as <1.5 g/ul).¹

SBP History

Spontaneous bacterial peritonitis portends bad outcomes. The one-year mortality rate after an episode of SBP is 30% to 50%.1 Furthermore, patients who have recovered from a previous episode of SBP have a 70% chance of developing another episode of SBP in that year.^1,2 In one study, norfloxacin was shown to decrease the one-year risk of SBP to 20% from 68% in patients with a history of SBP.³ Additionally, the likelihood of developing SBP from gram-negative bacilli was reduced to 3% from 60%. In order to be efficacious, norfloxacin must be given daily. When fluoroquinolones are prescribed less than once daily, there is a higher rate of fluoroquinolone resistant organisms in the stool.¹