Investigation of the clinical breakpoints of piperacillin-tazobactam against infections caused by Pseudomonas aeruginosa

Breaking Down the Breakpoints: Rationale for the 2022 Clinical and Laboratory Standards Institute Revised Piperacillin-Tazobactam Breakpoints Against Enterobacterales

Piperacillin-tazobactam (PTZ) is one of the most common antibiotics administered to hospitalized patients. Its broad activity against gram-negative, gram-positive, and anaerobic pathogens; efficacy in clinical trials across diverse infection types and patient populations; and generally favorable toxicity profile make it a particularly appealing antibiotic agent. PTZ susceptibility interpretive criteria (ie, breakpoints) for the Enterobacterales were initially established in 1992, as the drug was undergoing approval by the US Food and Drug Administration. In the ensuing 30 years, changes in the molecular epidemiology of the Enterobacterales and its impact on PTZ susceptibility testing, mounting pharmacokinetic/pharmacodynamic data generated from sophisticated techniques such as population pharmacokinetic modeling and Monte Carlo simulation, and disturbing safety signals in a large clinical trial prompted the Clinical Laboratory and Standards Institute (CLSI) to review available evidence to determine the need for revision of the PTZ breakpoints for Enterobacterales. After an extensive literature review and formal voting process, the susceptibility criteria were revised in the 2022 CLSI M100 document to the following: ≤8/4 µg/mL (susceptible), 16/4 µg/mL (susceptible dose-dependent), and ≥32/4 µg/mL (resistant). Herein, we provide a brief overview of the CLSI process of antibiotic breakpoint revisions and elaborate on the available data that ultimately led to the decision to revise the PTZ breakpoints.

Is Piperacillin-Tazobactam an Appropriate Empirical Agent for Hospital-Acquired Sepsis and Community-Acquired Septic Shock of Unknown Origin in Australia?

Early appropriate empirical antibiotics are critical for reducing mortality in sepsis. For hospital-acquired sepsis of unknown origin in Australia, piperacillin-tazobactam (TZP) is recommended as an empirical therapy. Anecdotally, some institutions also use TZP for community-acquired septic shock. This narrative review aimed to scrutinise the appropriateness of TZP as an empirical agent for undifferentiated hospital-acquired sepsis and community-acquired septic shock. An online database (Medline) was searched for relevant studies in adults published in the last 10 years. Studies were included if they addressed separately reported clinical outcomes related to a relevant aspect of TZP therapy in sepsis. Of 290 search results, no studies directly addressed the study aim. This review therefore explores several themes that emerged from the contemporary literature, all of which must be considered to fully interrogate the appropriateness of TZP use in this context. This review reveals the paucity and low quality of evidence available for TZP use in sepsis of unclear origin, while demonstrating the urgent need and equipoise for an Australian audit of TZP use in patients with sepsis of unknown origin.

Effect of elevated imipenem/cilastatin minimum inhibitory concentrations on patient outcomes in Gram-negative bloodstream infections

OBJECTIVES

Carbapenem minimum inhibitory concentration (MICs) are known to predict outcomes for patients with Gram-negative bacteraemia. However, limited data exist on how MICs influence such outcomes when organisms are classified as carbapenem-resistant. The purpose of this study was to evaluate the effect of increasing imipenem/cilastatin MICs on mortality in patients with Gram-negative bloodstream infection (BSI).

METHODS

Patients with an imipenem/cilastatin-resistant (MIC>4mg/L) monomicrobial Gram-negative BSI were eligible for inclusion in the study and were assessed for baseline characteristics, organ function, microbiological data, timing and type of therapeutic treatment, and in-hospital mortality.

RESULTS

A total of 62 patients with imipenem/cilastatin-resistant bacterial isolates (MIC>4mg/L) were retrospectively studied. Time to event analyses found no difference between patients who received carbapenem therapy and those who did not (P=0.10). After adjustment, patients receiving directed therapy were less likely to die (adjusted hazard ratio=0.35, 95% confidence interval 0.15-0.83; P<0.01), whereas higher modified Acute Physiology and Chronic Health Evaluation (APACHE) II score and days to positive culture were associated with non-survival.

CONCLUSION

This study did not demonstrate a relationship between receipt of a carbapenem and mortality in patients with carbapenem-resistant Gram-negative BSI.

Influence of borderline cefepime MIC on the outcome of cefepime-susceptible Pseudomonas aeruginosa bacteremia treated with a maximal cefepime dose: a hospital-based retrospective study

BACKGROUND

We assessed the influence of current cefepime minimal inhibitory concentration (MIC) breakpoints and the maximal cefepime dose on treatment outcomes in patients with bacteremia caused by cefepime-susceptible Pseudomonas aeruginosa.

METHODS

Adult patients hospitalized between July 2010 and June 2014 with a positive blood culture for cefepime-susceptible P. aeruginosa and receipt of cefepime as the primary therapy throughout the course were reviewed. Cefepime Etest^® MICs and clinical outcomes for P. aeruginosa bacteremia were reviewed to identify the MIC breakpoint influencing treatment outcomes.

RESULTS

Of the 90 patients enrolled, 49 (54.4%) were male (mean age = 66.8 years). The mean Acute Physiology and Chronic Health Evaluation II score was 22.01. Sixty patients (66.7%) received a maximal cefepime dose, and the 30-day crude mortality rate was 36.7%. MIC₉₀ of cefepime for P. aeruginosa was 8 mg/L. The cumulative survival rate at 30 days revealed that a lower cefepime MIC (<4 mg/L) for P. aeruginosa was associated with a higher survival rate than a higher MIC (≥4 mg/L) (72.6% vs. 23.5%, p < 0.0001). A cefepime MIC of ≥4 mg/L and age were independent risk factors for mortality, whereas the maximal cefepime dose was the independent protective factor. The use of a maximal cefepime dose did not improve the outcomes of patients with P. aeruginosa bacteremia at a MIC of ≥4 mg/L.

CONCLUSIONS

A cefepime MIC of 4 mg/L may predict an unfavorable outcome among patients with serious infections caused by P. aeruginosa, even the MICs still within the CLSI susceptibility breakpoint.

A propensity score-matched analysis of the impact of minimum inhibitory concentration on mortality in patients with Pseudomonas aeruginosa bacteraemia treated with piperacillin/tazobactam

The Clinical and Laboratory Standards Institute (CLSI) recently re-examined Pseudomonas aeruginosa minimum inhibitory concentration (MIC) susceptibility breakpoints for piperacillin/tazobactam (TZP). The objectives of this study were to analyse the impact of elevated TZP MICs (32-64 mg/L) versus lower respective MICs on P. aeruginosa bacteraemia patient outcomes. Data were gathered from a Veterans Health Administration national clinical database on P. aeruginosa bacteraemia episodes from 2007 to 2013. Patients treated with TZP were identified, comprising 53 elevated MIC episodes and 301 low MIC episodes. Propensity score matching (1:2 ratio) utilising independent variables associated with 30-day all-cause mortality was conducted to compare the outcomes of 53 elevated MIC episodes with 106 matched low MIC episodes. Independent baseline variables associated with 30-day all-cause mortality for all 354 episodes were hyperkalaemia, elevated blood urea nitrogen, elevated temperature, hypoglycaemia, lack of urinary source and thrombocytopenia. Similar 30-day all-cause mortality was found between the two propensity-matched TZP groups (elevated MIC 24.5% vs. low MIC 22.6%; P = 0.79).

A propensity score-matched analysis of the impact of minimum inhibitory concentration on mortality in patients with Pseudomonas aeruginosa bacteremia treated with cefepime or ceftazidime

The United States Clinical and Laboratory Standards Institute recently elected not to revise ceftazidime and cefepime Pseudomonas aeruginosa minimum inhibitory concentration (MIC) susceptibility breakpoints but rather recommended specific dosage regimens to correspond to breakpoints. This study's objective was to examine mortality of low and high MIC P. aeruginosa isolates in bacteremic patients treated with cefepime or ceftazidime. Data were gathered through a Veterans Health Administration national administrative database for veterans with P. aeruginosa blood cultures who received cefepime or ceftazidime. Seventy-four patients in the low MIC (≤2 μg/mL) group and 29 patients in the high (4-8 μg/mL) MIC group were included. Independent baseline variables associated with 30-day all-cause mortality were determined through multivariate analysis to calculate propensity scores and perform matching. All-cause 30-day mortality was not statistically significant between the 2 resultant propensity score-matched groups (17.2% mortality in the low MIC group versus 27.6% in the high MIC group; P=0.34). Data suggested that P. aeruginosa bacteremia episodes where the cephalosporin MIC = 8 μg/mL may have higher mortality, however this may be reflective of higher propensity scores. Our study suggests that it is reasonable to designate a cefepime or ceftazidime MIC ≤8 μg/mL as susceptible for P. aeruginosa bacteremia infections, but potential suboptimal outcomes in episodes for which the P. aeruginosa MIC is 8 μg/mL may need further investigation.

Impact of the MIC of piperacillin/tazobactam on the outcome for patients with bacteraemia due to Enterobacteriaceae: the Bacteraemia-MIC project

OBJECTIVE

Our objective was to evaluate the impact of low versus borderline MIC of piperacillin/tazobactam on the clinical outcomes of patients with bacteraemia caused by Enterobacteriaceae who were treated with that antimicrobial.

PATIENTS AND METHODS

A prospective observational multicentre cohort study was conducted in 13 Spanish university hospitals. Patients >17 years old with bacteraemia due to Enterobacteriaceae who received empirical piperacillin/tazobactam treatment for at least 48 h were included. Outcome variables were clinical response at day 21, clinical response at end of treatment with piperacillin/tazobactam and all-cause 30 day mortality. Univariate and multivariate logistic regression analyses were performed.

RESULTS

Overall, 275 patients were included in the analysis; 248 (90.2%) in the low MIC group (≤ 4 mg/L) and 27 (9.8%) in the borderline MIC group (8-16 mg/L). The biliary tract was the most common source of infection (48.4%) and Escherichia coli was the most frequent pathogen (63.3%). Crude 30 day mortality rates were 10.5% and 11.1% for the low MIC group and the borderline MIC group, respectively (relative risk = 1.06, 95% CI = 0.34-3.27, P = 1). Multivariate analysis of failure at day 21 and at end of treatment with piperacillin/tazobactam and 30 day mortality showed no trend towards increased clinical failure or mortality with borderline MICs (OR = 0.96, 95% CI = 0.18-4.88, P = 0.96; OR = 0.47, 95% CI = 0.10-2.26, P = 0.35; OR = 1.48, 95% CI = 0.33-6.68, P = 0.6).

CONCLUSIONS

We did not find that higher piperacillin/tazobactam MIC within the susceptible or intermediate susceptibility range had a significant influence on the outcome for patients with bacteraemia due to Enterobacteriaceae.

Does the piperacillin minimum inhibitory concentration for Pseudomonas aeruginosa influence clinical outcomes of children with pseudomonal bacteremia?

BACKGROUND

The Clinical and Laboratory Standards Institute (CLSI) recently elected to adjust the previous piperacillin susceptibility breakpoint of ≤64 µg/mL against Pseudomonas aeruginosa to ≤16 µg/mL, based largely on pharmacokinetic-pharmacodynamic (PK-PD) modeling studies. Data on whether PK-PD modeling correlates with clinical outcomes in children are needed before resorting to broader classes of antibiotics to treat P. aeruginosa.

METHODS

We performed a retrospective cohort study of children with P. aeruginosa bacteremia between 2001 and 2010 who were prescribed piperacillin. Baseline characteristics and clinical outcomes of children with piperacillin minimum inhibitory concentrations (MICs) of ≤16 µg/mL and of 32-64 µg/mL were compared. The primary outcome was 30-day mortality.

RESULTS

There were 170 children with P. aeruginosa bacteremia receiving piperacillin therapy who met inclusion criteria. One hundred twenty-four (72%) children had piperacillin MICs of ≤16 µg/mL and 46 (28%) children had piperacillin MICs of 32-64 µg/mL. There was no significant difference in baseline characteristics between the 2 groups. Thirty-day mortality was 9% and 24% in children with a piperacillin MIC of ≤16 µg/mL and of 32-64 µg/mL, respectively. Using multivariable logistic regression, children with elevated MICs had increased odds of mortality compared with children with lower MICs (odds ratio, 3.21; 95% confidence interval, 1.26-8.16).

CONCLUSIONS

Our finding that elevated piperacillin MICs are associated with higher mortality in children supports the recent CLSI recommendation to lower the breakpoint of piperacillin against P. aeruginosa to ≤16 µg/mL. Alternate therapeutic choices should be considered when piperacillin MICs against P. aeruginosa are ≥32 µg/mL.

Impact of antibiotic MIC on infection outcome in patients with susceptible Gram-negative bacteria: a systematic review and meta-analysis

The objective of this study was to analyze the impact of MIC values within the susceptible range of antibiotics on the outcomes of patients with Gram-negative infections. The PubMed and Scopus electronic databases were searched. We identified 13 articles (1,469 patients) that studied the impact of antibiotic MICs on the outcomes of infections; β-lactams were studied in 10 of them. Infections due to Salmonella enterica strains with high fluoroquinolone MICs were associated with more treatment failures than those due to strains with low MICs (relative risk [RR], 5.75; 95% confidence interval [CI], 1.77 to 18.71). Among non-Salmonella enterobacteriaceae, there was no difference in treatment failures depending on the MIC value (RR, 1.18; 95% CI, 0.71 to 1.97); however, a higher all-cause mortality was observed for patients infected with strains with high MICs (RR, 2.03; 95% CI, 1.05 to 3.92). More treatment failures were observed for patients infected with nonfermentative Gram-negative bacilli when strains had high MICs (RR, 5.54; 95% CI, 2.72 to 11.27). The mortality rate for patients with infections with Gram-negative nonfermentative bacilli with high MICs was also higher than for those with low MICs (RR, 2.39; 95% CI, 1.19 to 4.81). The limited available data suggest that there is an association between high MICs, within the susceptible range, and adverse outcomes for patients with Gram-negative infections.