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How does one decide the best pharmacotherapeutic strategy for bacterial peritonitis?

In a recent issue of Expert Opinion on Pharmacotherapy, Maraolo et al. presented an outstanding review on the pharmacological treatment of bacterial peritonitis [1]. The authors focused on spontaneous bacterial peritonitis (SBP), a form of bacterial peritonitis occurring almost exclusively in patients with liver cirrhosis. They highlight that selection of the appropriate empiric antibiotic drug has become a challenge. In 2010, the guidelines of the European Association for the Study of the Liver (EASL) stated that treatment with third-generation cephalosporines led to resolution of SBP in 77–98% of patients [2]. Nowadays, resistance to third-generation cephalosporines is reported in up to 58% [3], with no single antibiotic drug to replace third-generation cephalosporines with the same efficacy known from the past. The decreasing efficacy of thirdgeneration cephalosporins is not only due to the general rise of multiresistant bacteria, but also caused by a shift toward infections with Gram-positive bacteria in SBP [4]. Both developments correspond to the widespread use of quinolones in the primary and secondary prophylaxis of SBP [2]. In the light of these developments, how does one decide on empirical treatment of bacterial peritonitis in clinical day to day work? The first crucial step is to distinguish with which form of bacterial peritonitis the patient presents: SBP occurs in general only in patients suffering from advanced liver disease. In patients without liver cirrhosis, secondary bacterial peritonitis due to intestinal perforation or intra-abdominal abscess formation is much more frequent than SBP and requires surgical or interventional treatment in conjunction with antibiotic drug therapy. In case of polymicrobial peritonitis or clinical signs of intestinal perforation, a CT scan should be performed also in patients with liver cirrhosis and suspected SBP to rule out secondary peritonitis [2]. Peritonitis in patients on continuous ambulatory peritoneal dialysis is characterized by a different pattern of causative bacteria, mostly Gram-positive bacteria [5]. Rare forms of bacterial peritonitis are tuberculous or chlamydial peritonitis. SBP is confirmed in patients with liver cirrhosis if the neutrophil count in the ascites exceeds 250 cells/μL [2]. Rapid start of an effective antibiotic treatment improves survival [6,7]. However, selection of the appropriate empiric antibiotic drug is complicated by the rise of antimicrobial resistance and the variety of bacteria possibly causing SBP, with Escherichia coli, the most frequent pathogen, being identified in only 33% of cases [8]. Detection of bacteria relies on conventional culture of ascites transferred at the bedside in blood culture bottles and takes at least 2 days. However, in a significant proportion of patients, ascites culture will remain negative [9], most probably because of low bacterial loads in the ascites. Thus, we face uncertainty on which antibiotic to choose while knowing that failing to select the right drugmay worsen the prognosis of the patient [10]. How can we overcome this situation? We may choose a combination of broad spectrum antibiotics which will most likely cover all possibilities. Piano and coauthors reported that the combination of meropenem plus daptomycin led to resolution of SBP in 13/15 (87%) versus 4/16 (25%) patients treated with ceftazidime in nosocomial SBP (p < 0.001) [11]. Because frequent use of carbapenems has been linked to a rise in carbapenem-resistant infections, a significant downside of such an approach is the induction of colonization and infection with carbapenem-resistant Enterobacteriaceae [12]. Given the limited number of new antibiotic drugs in development, the widespread use of carbapenems carries the risk of inducing resistance which will prevent effective treatment in the future. In addition, the combination therapy did not lead to lower in-hospital mortality or higher 30-day or 90-day transplant free survival [11]. Moreover, the optimal dosage of daptomycin to treat enterococci, a frequent cause of SBP, is still debated [13]. Thus, a broad combination therapy might be helpful for the resolution of infection, but the impact onmortality in SBP is not clear andwe risk future treatment failure. This is particularly important because SBP is an infection with a high rate of recurrence [2]. To limit the use of broad spectrum and last resort antibiotics, we need parameters to identify patients at risk for resistance to common antibiotics. First, substantial regional differences in the prevalence of antibiotic resistance should be considered. In nosocomial SBP, for example, resistance to third-generation cephalosporines was detected in 83% of patients from Italy [11] compared to 30% of patients from Germany [10]. Therefore, knowing the local resistance pattern is essential [14]. However, it is a challenge to acquire this knowledge for different forms of infection and to keep it up to date. In addition, a general analysis of detected microorganisms from peritoneal fluid may not be indicative for pathogens relevant for SBP, because other forms of bacterial peritonitis present with different microbial patterns. Furthermore, bacteria identified in the ascites without elevation