Ascites is the most common hepatic decompensation, occurring in 50% of cirrhotic patients followed for over a decade ¹ . The development of ascites heralds a vulnerable time of sharply increased mortality for patients with liver disease – related in large part to spontaneous bacterial peritonitis (SBP) ^{2, 3} . SBP is an infection of the ascitic fluid that occurs in 10–30% of patients with ascites ⁴ . Fatal in as many as 32.6% of cases, SBP can have a profound effect on the tenuous hemodynamics of patients with cirrhosis ⁵ . Exacerbating the arterial underfilling that results from the splanchnic vasodilation of cirrhosis, SBP may lead to a decrease in cardiac output such that it can no longer satisfy the needs of a kidney that is already vasoconstricted ⁶ . The result is the hepatorenal syndrome which is often devastating. SBP with renal injury is fatal in 42% of patients ⁷ .

SBP is caused by translocation of gastrointestinal organisms into the ascitic fluid, most commonly Escherichia coli, Klebsiella pneumoniae and Streptococcus pneumoniae. As such, third generation cephalosporins are amongst the best studied antibiotics in this setting, with ceftriaxone as the drug of choice where cefotaxime is not available. Studied as a treatment for SBP in clinical trials for 25 years, the doses employed were either 1 g every 12 hours or 2 g every 24 hours given intravenously for 5 to 10 day courses ^{8– 14} .

At our center, we have found that ceftriaxone is often given at 1 g daily either in reference to online resources from other major teaching institutions or because 1 g is the general preset dose for this antibiotic as generated by the electronic ordering system ¹⁵ . ( http://clinicalpharmacy.ucsf.edu/idmp/adult_guide/empiric_guide/intraabd_hosp_frame.htm, last accessed 1-12-2014). The outcomes of SBP as a function of ceftriaxone dosage – 1 g daily versus 2 g daily – have never been evaluated. It is unknown what effect the dosage of ceftriaxone has on the control of SBP or on mortality. Neither the American Association for the Study of Liver Disease (AASLD) nor the European Association for the Study of the Liver (EASL) guidelines on SBP management explicitly comment on the dosing of ceftriaxone for this indication ^{16, 17} .

Herein we present the results of a retrospective review of the outcomes of SBP stratified by dose of ceftriaxone. This study aims to determine the additional benefit of the extra gram of ceftriaxone when treating SBP in the clinically relevant terms of renal injury and mortality.

This is a retrospective, single center review of prospectively maintained medical records for all consecutive patients treated with ceftriaxone for SBP at the Beth Israel Deaconess Medical Center, Boston, USA, between January 2003 and December 2011.

We searched our clinical database for all patients that received ceftriaxone within 48 hours of a peritoneal fluid cell count and differential drawn in the emergency department or hospital ward. We then limited the population to those with 250 or more neutrophils in the ascites. Patient charts were then examined to exclude those with a prior liver transplant, evidence of intra-abdominal source of infection [abscess, perforation, recent (within 2 weeks) intra-abdominal surgery], peritoneal dialysis, or documentation of a secondary infection (urinary tract infection, pneumonia, blood stream infection, cellulitis, meningitis) for which ceftriaxone was started prior to the peritoneal fluid collection. We collected data on age, sex, Model for End Stage Liver Disease (MELD) score (bilirubin, creatinine and PT/INR) at diagnosis, peritoneal white blood cell count and differential, blood and peritoneal culture data, dose of ceftriaxone, additional antibiotics, duration of antibiotic therapy, creatinine trends, intensive care utilization, length of hospital stay and mortality.

Statistics were performed using SAS 9.2 and included student’s t-test, multivariate regression analysis, and log-rank testing/survival analysis where appropriate. P-value of 0.05 was considered significant for all analyses. While no prior studies have examined the effect of ceftriaxone dosing in order to determine study power, prior studies of ceftriaxone for SBP may be instructive. For example, in comparing 2 g ceftriaxone to cefonicid, the in-hospital death rate during therapy was 13% versus 30% which, assuming an alpha of 0.05, a sample size of 91 gives an 80% power ¹³ . However, when examining the broader literature on ceftriaxone, regimens of variable duration (5 vs. 10 days) with 30% vs. 35% 30 day mortality would imply that studies require more than 1600 patients for adequate power ^{8– 14} .

We found 138 patients with SBP treated with ceftriaxone. Of these, 91 patients met our inclusion criteria: 34 patients received 1 g daily and 57 received 2 g (total) daily. There was no significant difference between the groups with respect to age, gender, MELD score, peritoneal culture positivity or other infectious burden ( Table 1). All patients had received a protocol of albumin infusion on days 1 and 3 after the diagnosis of SBP in accordance with best practice ¹⁸ .

We next compared the hospital course for patients that received either dose of ceftriaxone ( Table 2). While both groups were likely to be treated with at least one additional antibiotic during their hospitalization (74% of those treated with 1 g, and 61% of those treated with 2 g), this difference was not significant. The total course of antibiotics – ceftriaxone or otherwise – was also similar between groups. The group receiving 2 g ceftriaxone daily did have a trend towards a shorter hospital stay, although this did not meet statistical significance (13.24 days vs. 10.28, p = 0.44). We did see a statistically significant shorter average length of intensive unit (ICU) stay in patients who received 2 g ceftriaxone a day (0.59 ± 1.78 days), compared to those who received 1 g ceftriaxone daily (3.26 ± 6.9 days) (p = 0.034). The odds ratio for ICU utilization was 0.11 (95% CI 0.02–0.65). However, this difference was no longer significant after controlling for MELD score - odds ratio 0.21 (95% CI 0.04–1.07). Finally, we examined one-year survival for patients treated with 1 versus 2 g ceftriaxone, and found a significant improvement in survival associated with the 2 g dose (p 0.0034 log rank test) ( Figure 1). Median overall survival was greater for patients treated with the 2 g dose (228 days vs. 102 days, however it was not significant (p = 0.26).

Given the high prevalence of additional antibiotic treatment, we also examined the pattern of antibiotic use. Overall, 70% of patients were treated with at least one additional antibiotic. The duration of antibiotic use, as well as the number and type of antibiotics prescribed were highly variable ( Table 3). While vancomycin was the most common concurrent antibiotic, used in 46% of patients, over 25 different medications were used in a variety of combinations. To further understand the antibiotic regimens observed, we next examined the available culture data. Of 91 patients diagnosed with SBP on neutrophil criteria, 13 were culture-positive. Of these, one patient had a documented infection resistant to ceftriaxone. This patient was excluded from the analysis. 14 patients had evidence of a secondary infection ( Table 1). These included pneumonia (diagnosed with chest x-ray), urinary tract infection (>100,000 colonies on urine dipstick with positive urine culture), and cellulitis (clinical diagnosis documented in chart).

Our study of ceftriaxone dosage for SBP yielded two core findings. First, a total ceftriaxone dose of 2 g daily over 1 g daily exhibited a non-significant reduction of intensive care utilization by cirrhotic patients with SBP, controlling for MELD score. Similarly, there was a trend towards improved mortality with the 2 g dosage. Prospective studies in a larger cohort are indicated to explore the true significance of these results. While it could explain our results, whether the pharmacodynamics of intravenous ceftriaxone are such that the peritoneal drug concentration following a 1 g infusion results in slower control of infection is unclear from our study ¹⁹ . Second, the number, duration and complexity of antibiotic regimens that cirrhotic patients experience is highly variable. The reasons for this finding are unclear and deserve further study in order to understand both the physician and patient factors that increase antibiotic regimen complexity as well as the effect on outcomes including mortality, morbidity and future infection with resistant organisms.

This study emphasizes the need for antibiotic stewardship and treatment standardization in the care of cirrhotic patients. We feel this can be easily achieved by computer programming. For centers that use electronic provider order entry, a preset dose of 2 g of ceftriaxone when prescribing for a diagnosis of SBP can ensure standardized and appropriate dosing. Our findings are inconclusive but suggestive of a benefit from a higher ceftriaxone dose. As a result, we have programmed a prompt into ceftriaxone orders that asks the physician to specify whether the medication is intended to treat SBP. This selection results in an automatic 2 g daily dose ( Figure 2). Cirrhotic patients can be admitted to any service of the hospital, including those staffed by hepatologists, internists, surgeons and intensivists. By standardizing care delivery, the healthcare system can ensure that the medications cirrhotic patients receive are dosed appropriately for their needs. Furthermore, by programming a menu-selection for SBP, our hospital - or any hospital with similar capabilities - may track the disease indications for each antibiotic allowing for audits and outreach.

Our conclusions are limited in a few ways. First, our study is retrospective and therefore we cannot comment on the impact of other treatment decisions that may or may not be associated with the dose of ceftriaxone chosen. Additionally, we cannot exclude the possibility that our study was underpowered to detect a difference between treatment groups. Second, the microbiology of our patients’ SBP is unclear given the low rate of culture positivity so we cannot comment on the impact of antimicrobial resistance. Third, follow-up paracenteses to confirm resolution of the SBP after antibiotic treatment were infrequent and thus we cannot comment on the rate of resolution of neutrophilia as function of ceftriaxone dose.

In order to prevent unwanted practice variation, we recommend standardizing the treatment of SBP by automating the dose of ceftriaxone in the provider order entry system. Further research must be aimed at rationalizing the antibiotic regimens employed in the treatment of cirrhotic patients. Programs to this end include fastidious antibiotic stewardship facilitated by computerized audits of indication-based antibiotic usage and improved microbial culture and detection techniques.

The data referenced by this article are under copyright with the following copyright statement: Copyright: � 2014 Mazer L et al.

Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

figshare: Spontaneous bacterial peritonitis outcome and ceftriaxone dosage data, http://dx.doi.org/10.6084/m9.figshare.931754 ²⁰