Meropenem for treating KPC-producing Klebsiella pneumoniae bloodstream infections: Should we get to the PK/PD root of the paradox?

Infections in lung transplanted patients: A review

Lung transplantation can improve the survival of patients with severe chronic pulmonary disorders. However, the short- and long-term risk of infections can increase morbidity and mortality rates. A non-systematic review was performed to provide the most updated information on pathogen, host, and environment-related factors associated with the occurrence of bacterial, fungal, and viral infections as well as the most appropriate therapeutic options. Bacterial infections account for about 50% of all infectious diseases in lung transplanted patients, while viruses represent the second cause of infection accounting for one third of all infections. Almost 10% of patients develop invasive fungal infections during the first year after lung transplant. Pre-transplantation comorbidities, disruption of physical barriers during the surgery, and exposure to nosocomial pathogens during the hospital stay are directly associated with the occurrence of life-threatening infections. Empiric antimicrobial treatment after the assessment of individual risk factors, local epidemiology of drug-resistant pathogens and possible drug-drug interactions can improve the clinical outcomes.

Treatment and diagnosis of severe KPC-producing Klebsiella pneumoniae infections: a perspective on what has changed over last decades

Antimicrobial resistance is a global health threat. Among Gram-negative bacteria, resistance to carbapenems, a class of β-lactam antibiotics, is usually a proxy for difficult-to-treat resistance, since carbapenem-resistant organisms are often resistant to many classes of antibiotics. Carbapenem resistance in the Gram-negative pathogen Klebsiella pneumoniae is mostly due to the production of carbapenemases, enzymes able to hydrolyze carbapenems, and K. pneumoniae carbapenemase (KPC)-type enzymes are overall the most prevalent carbapenemases in K. pneumoniae. In the last decade, the management of severe infections due to KPC-producing K. pneumoniae (KPC-Kp) in humans has presented many peculiar challenges to clinicians worldwide. In this perspective, we discuss how the treatment of severe KPC-Kp infections has evolved over the last decades, guided by the accumulating evidence from clinical studies, and how recent advances in diagnostics have allowed to anticipate identification of KPC-Kp in infected patients.KEY MESSAGESIn the last decade, the management of severe infections due to KPC-Kp has presented many peculiar challenges to clinicians worldwideFollowing the introduction in clinical practice of novel β-lactam/β-lactamase inhibitor combinations and novel β-lactams active against KPC-producing bacteria, the management of severe KPC-Kp infections has witnessed a remarkable evolutionTreatment of severe KPC-Kp infections is a highly dynamic process, in which the wise use of novel antimicrobials should be accompanied by a continuous refinement based on evolving clinical evidence and laboratory diagnostics.

Extended Versus Intermittent Meropenem Infusion in the Treatment of Nosocomial Pneumonia: A Retrospective Single-Center Study

The efficacy of extended meropenem infusions in patients with nosocomial pneumonia is not well defined. Therefore, we compared the clinical outcomes of extended versus intermittent meropenem infusions in the treatment of nosocomial pneumonia. We performed a retrospective analysis of extended versus intermittent meropenem infusions in adult patients who had been treated for nosocomial pneumonia at a medical ICU between 1 May 2018 and 30 April 2020. The primary outcome was mortality at 14 days. Overall, 64 patients who underwent an extended infusion and 97 with an intermittent infusion were included in this study. At 14 days, 10 (15.6%) patients in the extended group and 22 (22.7%) in the intermittent group had died (adjusted hazard ratio (HR), 0.55; 95% confidence interval (CI): 0.23-1.31; p = 0.174). In the subgroup analysis, significant differences in mortality at day 14 were observed in patients following empirical treatment with meropenem (adjusted HR, 0.17; 95% CI: 0.03-0.96; p = 0.045) and in Gram-negative pathogens identified by blood or sputum cultures (adjusted HR, 0.01; 95% CI: 0.01-0.83; p = 0.033). Extended infusion of meropenem compared with intermittent infusion as a treatment option for nosocomial pneumonia may have a potential advantage in specific populations.

Mortality-Related Risk Factors and Novel Antimicrobial Regimens for Carbapenem-Resistant Enterobacteriaceae Infections: A Systematic Review

OBJECTIVE

Carbapenem-resistant Enterobacteriaceae (CRE) has become a significant public health problem in the last decade. We aimed to explore the risk factors of mortality in patients with CRE infections and to focus on the current evidence on antimicrobial regimens for CRE infections, particularly from the perspective of mortality.

METHODS

A systematic literature review was performed by searching the databases of EMBASE, PubMed, and the Cochrane Library to identify studies that evaluated mortality-related risk factors and antimicrobial regimens for CRE infections published from 2012 to 2022.

RESULTS

In total, 33 and 28 studies were included to analyze risk factors and antibiotic treatment, respectively. The risk factors most frequently reported as significantly associated with CRE mortality were antibiotic use (92.9%; 26/28 studies), comorbidities (88.7%; 23/26 studies), and hospital-related factors (82.8%; 24/29 studies). In 10 studies that did not contain ceftazidime/avibactam (CAZ-AVI) therapy, seven demonstrated significantly lower mortality in combination therapy than in monotherapy. However, 5 of 6 studies identified no substantial difference between CAZ-AVI monotherapy and CAZ-AVI combination therapy. Six studies reported substantially lower mortality in CAZ-AVI regimens than in other regimens.

CONCLUSION

Several risk factors, particularly antibiotic use and patients' comorbidities, are strong risk factors for CRE mortality. The optimal regimen for CRE infections remains controversial. Combination therapy should be considered when carbapenems, colistin, tigecycline, or aminoglycosides are administered. CAZ-AVI appears to be a promising antibiotic for CRE infections. Most importantly, treatment should be individualized according to the source and severity of the disease or other highly related risk factors.

Ceftolozane/tazobactam for hospital-acquired/ventilator-associated bacterial pneumonia due to ESBL-producing Enterobacterales: a subgroup analysis of the ASPECT-NP clinical trial

BACKGROUND

After the MERINO trial with piperacillin/tazobactam, the efficacy of β-lactam/tazobactam combinations in serious infections involving extended-spectrum β-lactamase (ESBL)-producing pathogens merits special evaluation.

OBJECTIVES

To further confirm the efficacy of ceftolozane/tazobactam in treating hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP) involving ESBL-positive and/or AmpC-producing Enterobacterales.

METHODS

Retrospective subgroup analysis of the ASPECT-NP trial comparing ceftolozane/tazobactam with meropenem for treating HABP/VABP in mechanically ventilated adults (ClinicalTrials.gov NCT02070757). ESBLs were identified using whole genome sequencing. Chromosomal AmpC production was quantified employing a high-sensitivity mRNA transcription assay.

RESULTS

Overall, 61/726 (8.4%) participants had all baseline lower respiratory tract (LRT) isolates susceptible to both study treatments and ≥1 baseline ESBL-positive/AmpC-overproducing Enterobacterales isolate. In this subgroup (ceftolozane/tazobactam n = 30, meropenem n = 31), baseline characteristics were generally comparable between treatment arms. The most frequent ESBL-positive and/or AmpC-overproducing Enterobacterales isolates (ceftolozane/tazobactam n = 31, meropenem n = 35) overall were Klebsiella pneumoniae (50.0%), Escherichia coli (22.7%), and Proteus mirabilis (7.6%). The most prevalent ESBLs were CTX-M-15 (75.8%), other CTX-M (19.7%), and SHV (4.5%); 10.6% of isolates overproduced chromosomal AmpC. Overall, 28 day all-cause mortality was 6.7% (2/30) with ceftolozane/tazobactam and 32.3% (10/31) with meropenem (25.6% difference, 95% CI: 5.54 to 43.84). Clinical cure rate at test-of-cure, 7-14 days after end of therapy, was 73.3% (22/30) with ceftolozane/tazobactam and 61.3% (19/31) with meropenem (12.0% difference, 95% CI: -11.21 to +33.51). Per-isolate microbiological response at test-of-cure was 64.5% (20/31) with ceftolozane/tazobactam and 74.3% (26/35) with meropenem (-9.8% difference, 95% CI: -30.80 to +12.00).

CONCLUSIONS

These data confirm ceftolozane/tazobactam as an effective treatment option for HABP/VABP involving ceftolozane/tazobactam-susceptible ESBL-positive and/or AmpC-producing Enterobacterales.

Ceftolozane/tazobactam versus meropenem in patients with ventilated hospital-acquired bacterial pneumonia: subset analysis of the ASPECT-NP randomized, controlled phase 3 trial

Background

Ceftolozane/tazobactam is approved for treatment of hospital-acquired/ventilator-associated bacterial pneumonia (HABP/VABP) at double the dose approved for other infection sites. Among nosocomial pneumonia subtypes, ventilated HABP (vHABP) is associated with the lowest survival. In the ASPECT-NP randomized, controlled trial, participants with vHABP treated with ceftolozane/tazobactam had lower 28-day all-cause mortality (ACM) than those receiving meropenem. We conducted a series of post hoc analyses to explore the clinical significance of this finding.

Methods

ASPECT-NP was a multinational, phase 3, noninferiority trial comparing ceftolozane/tazobactam with meropenem for treating vHABP and VABP; study design, efficacy, and safety results have been reported previously. The primary endpoint was 28-day ACM. The key secondary endpoint was clinical response at test-of-cure. Participants with vHABP were a prospectively defined subgroup, but subgroup analyses were not powered for noninferiority testing. We compared baseline and treatment factors, efficacy, and safety between ceftolozane/tazobactam and meropenem in participants with vHABP. We also conducted a retrospective multivariable logistic regression analysis in this subgroup to determine the impact of treatment arm on mortality when adjusted for significant prognostic factors.

Results

Overall, 99 participants in the ceftolozane/tazobactam and 108 in the meropenem arm had vHABP. 28-day ACM was 24.2% and 37.0%, respectively, in the intention-to-treat population (95% confidence interval [CI] for difference: 0.2, 24.8) and 18.2% and 36.6%, respectively, in the microbiologic intention-to-treat population (95% CI 2.5, 32.5). Clinical cure rates in the intention-to-treat population were 50.5% and 44.4%, respectively (95% CI − 7.4, 19.3). Baseline clinical, baseline microbiologic, and treatment factors were comparable between treatment arms. Multivariable regression identified concomitant vasopressor use and baseline bacteremia as significantly impacting ACM in ASPECT-NP; adjusting for these two factors, the odds of dying by day 28 were 2.3-fold greater when participants received meropenem instead of ceftolozane/tazobactam.

Conclusions

There were no underlying differences between treatment arms expected to have biased the observed survival advantage with ceftolozane/tazobactam in the vHABP subgroup. After adjusting for clinically relevant factors found to impact ACM significantly in this trial, the mortality risk in participants with vHABP was over twice as high when treated with meropenem compared with ceftolozane/tazobactam.

Trial registration

clinicaltrials.gov, NCT02070757. Registered 25 February, 2014, clinicaltrials.gov/ct2/show/NCT02070757.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03694-3.

Pitfalls in genotypic antimicrobial susceptibility testing caused by low expression of blaKPC in Escherichia coli

BACKGROUND

There is a growing interest in the rapid genotypic identification of antimicrobial resistance (AMR). In routine diagnostics, we detected multiple KPC-positive Escherichia coli (KPC-Ec) with discordant phenotypic meropenem susceptibility from a single patient's blood cultures, which prompted a more thorough investigation.

OBJECTIVES

We investigated the potential clinical relevance of, and the mechanism behind, discordant phenotypic and genotypic meropenem susceptibility in KPC-Ec.

METHODS

WGS was used to perform a comparative analysis of the isolates' genetic characteristics and their blaKPC-2 locus. Expression of blaKPC-2 was determined by quantitative PCR and the potency of meropenem hydrolysis was determined using a semi-quantitative carbapenem inactivation method. An in vivo infection assay using Galleria mellonella was performed to assess the potential clinical relevance of KPC expression in E. coli.

RESULTS

Despite the presence of blaKPC-2, three of five isolates were susceptible to meropenem (MICVITEK2 ≤ 0.25 mg/L), while two isolates were resistant (MICVITEK2 ≥ 16 mg/L). The isolates with high MICs had significantly higher blaKPC-2 expression, which corresponds to phenotypic meropenem inactivation. The genetic environment of blaKPC-2, which may impact KPC production, was identical in all isolates. In vivo infection assay with G. mellonella suggested that meropenem was effective in reducing mortality following infection with low-expressing KPC-Ec.

CONCLUSIONS

Our findings clearly highlight a limitation of genotypic AMR prediction for blaKPC. For the time being, genotypic AMR prediction requires additional analysis for accurate antibiotic therapy decision-making.

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

Despite the recent development of antibacterials that are active against multidrug-resistant pathogens, drug combinations are often necessary to optimize the killing of difficult-to-treat organisms. Antimicrobial combinations typically are composed of multiple agents that are active against the target organism; however, many studies have investigated the potential utility of combinations that consist of one or more antibacterials that individually are incapable of killing the relevant pathogen. The current review summarizes in vitro, in vivo, and clinical studies that evaluate combinations that include at least one drug that is not active individually against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, or Staphylococcus aureus. Polymyxins were often included in combinations against all three of the Gram-negative pathogens, and carbapenems were commonly incorporated into combinations against K. pneumoniae and A. baumannii. Minocycline, sulbactam, and rifampin were also frequently investigated in combinations against A. baumannii, whereas the addition of ceftaroline or another β-lactam to vancomycin or daptomycin showed promise against S. aureus with reduced susceptibility to vancomycin or daptomycin. Although additional clinical studies are needed to define the optimal combination against specific drug-resistant pathogens, the large amount of in vitro and in vivo studies available in the literature may provide some guidance on the rational design of antibacterial combinations.

Systematic review and meta-analysis of in vitro efficacy of antibiotic combination therapy against carbapenem-resistant Gram-negative bacilli

The superiority of combination therapy for carbapenem-resistant Gram-negative bacilli (CR-GNB) infections remains controversial. In vitro models may predict the efficacy of antibiotic regimens against CR-GNB. A systematic review and meta-analysis was performed including pharmacokinetic/pharmacodynamic (PK/PD) and time-kill (TK) studies examining the in vitro efficacy of antibiotic combinations against CR-GNB [PROSPERO registration no. CRD42019128104]. The primary outcome was in vitro synergy based on the effect size (ES): high, ES ≥ 0.75, moderate, 0.35 < ES < 0.75; low, ES ≤ 0.35; and absent, ES = 0). A network meta-analysis assessed the bactericidal effect and re-growth rate (secondary outcomes). An adapted version of the ToxRTool was used for risk-of-bias assessment. Over 180 combination regimens from 136 studies were included. The most frequently analysed classes were polymyxins and carbapenems. Limited data were available for ceftazidime/avibactam, ceftolozane/tazobactam and imipenem/relebactam. High or moderate synergism was shown for polymyxin/rifampicin against Acinetobacter baumannii [ES = 0.91, 95% confidence interval (CI) 0.44-1.00], polymyxin/fosfomycin against Klebsiella pneumoniae (ES = 1.00, 95% CI 0.66-1.00) and imipenem/amikacin against Pseudomonas aeruginosa (ES = 1.00, 95% CI 0.21-1.00). Compared with monotherapy, increased bactericidal activity and lower re-growth rates were reported for colistin/fosfomycin and polymyxin/rifampicin in K. pneumoniae and for imipenem/amikacin or imipenem/tobramycin against P. aeruginosa. High quality was documented for 65% and 53% of PK/PD and TK studies, respectively. Well-designed in vitro studies should be encouraged to guide the selection of combination therapies in clinical trials and to improve the armamentarium against carbapenem-resistant bacteria.

Cefiderocol versus high-dose, extended-infusion meropenem for the treatment of Gram-negative nosocomial pneumonia (APEKS-NP): a randomised, double-blind, phase 3, non-inferiority trial

BACKGROUND

Nosocomial pneumonia due to multidrug-resistant Gram-negative pathogens poses an increasing challenge. We compared the efficacy and safety of cefiderocol versus high-dose, extended-infusion meropenem for adults with nosocomial pneumonia.

METHODS

We did a randomised, double-blind, parallel-group, phase 3, non-inferiority trial in 76 centres in 17 countries in Asia, Europe, and the USA (APEKS-NP). We enrolled adults aged 18 years and older with hospital-acquired, ventilator-associated, or health-care-associated Gram-negative pneumonia, and randomly assigned them (1:1 by interactive response technology) to 3-h intravenous infusions of either cefiderocol 2 g or meropenem 2 g every 8 h for 7-14 days. All patients also received open-label intravenous linezolid (600 mg every 12 h) for at least 5 days. An unmasked pharmacist prepared the assigned treatments; investigators and patients were masked to treatment assignment. Only the unmasked pharmacist was aware of the study drug assignment for the infusion bags, which were administered in generic infusion bags labelled with patient and study site identification numbers. Participants were stratified at randomisation by infection type and Acute Physiology and Chronic Health Evaluation II (APACHE II) score (≤15 and ≥16). The primary endpoint was all-cause mortality at day 14 in the modified intention-to-treat (ITT) population (ie, all patients receiving at least one dose of study drug, excluding patients with Gram-positive monomicrobial infections). The analysis was done for all patients with known vital status. Non-inferiority was concluded if the upper bound of the 95% CI for the treatment difference between cefiderocol and meropenem groups was less than 12·5%. Safety was investigated to the end of the study in the safety population, which included all patients who received at least one dose of study drug. This trial is registered with ClinicalTrials.gov, NCT03032380, and EudraCT, 2016-003020-23.

FINDINGS

Between Oct 23, 2017, and April 14, 2019, we randomly assigned 148 participants to cefiderocol and 152 to meropenem. Of 292 patients in the modified ITT population, 251 (86%) had a qualifying baseline Gram-negative pathogen, including Klebsiella pneumoniae (92 [32%]), Pseudomonas aeruginosa (48 [16%]), Acinetobacter baumannii (47 [16%]), and Escherichia coli (41 [14%]). 142 (49%) patients had an APACHE II score of 16 or more, 175 (60%) were mechanically ventilated, and 199 (68%) were in intensive care units at the time of randomisation. All-cause mortality at day 14 was 12·4% with cefiderocol (18 patients of 145) and 11·6% with meropenem (17 patients of 146; adjusted treatment difference 0·8%, 95% CI -6·6 to 8·2; p=0·002 for non-inferiority hypothesis). Treatment-emergent adverse events were reported in 130 (88%) of 148 participants in the cefiderocol group and 129 (86%) of 150 in the meropenem group. The most common treatment-emergent adverse event was urinary tract infection in the cefiderocol group (23 patients [16%] of 148) and hypokalaemia in the meropenem group (23 patients [15%] of 150). Two participants (1%) of 148 in the cefiderocol group and two (1%) of 150 in the meropenem group discontinued the study because of drug-related adverse events.

INTERPRETATION

Cefiderocol was non-inferior to high-dose, extended-infusion meropenem in terms of all-cause mortality on day 14 in patients with Gram-negative nosocomial pneumonia, with similar tolerability. The results suggest that cefiderocol is a potential option for the treatment of patients with nosocomial pneumonia, including those caused by multidrug-resistant Gram-negative bacteria.

FUNDING

Shionogi.

Does dose reduction of renally cleared antibiotics in patients with impaired renal function lead to adequate drug exposure? A systematic review

BACKGROUND

There is inconsistency between many guidelines in the recommended dose reduction of renally cleared antibiotics in patients with impaired renal function.

OBJECTIVES

This systematic review summarizes the available evidence on the adequacy of the recommended dose reduction in terms of achieving sufficient antibiotic drug exposure or pharmacokinetic/pharmacodynamic target attainment after treatment with these reduced doses.

DATA SOURCES

We systematically searched Ovid Medline and Embase from inception (respectively 1946 and 1947) through July 2019.

STUDY ELIGIBILITY CRITERIA

All studies reporting antibiotic drug exposure and/or pharmacokinetic/pharmacodynamic (PK/PD) target attainment after dose reduction of antibiotics in patients with impaired renal function.

PARTICIPANTS

Adult patients with or without infections.

INTERVENTIONS

Administration of reduced doses of antibiotics (orally, intravenously or intramuscularly).

METHODS

The reduced dose was considered adequate when the most relevant parameters of drug exposure or PK/PD target attainment in patients with impaired renal function were within a range of 80% to 125% of that patients with adequate renal function receiving a regular dose (reference) or when PK/PD target attainment was attained in at least 90% of the patients with impaired renal function, regardless of the lack of a reference group.

RESULTS

Twenty-seven of the 4202 identified studies were included. The quality of 15 of 27 studies was fair, and most studies were of β-lactams (12/27). Best evidence was available for meropenem: four studies were included, of which two studies were of good quality. Drug exposure for meropenem is 158% to 286% higher in patients with impaired renal function receiving reduced doses compared to patients with adequate renal function receiving regular doses. For all other antibiotics, a maximum of one good-quality study could be identified.

CONCLUSIONS

No good-quality evidence on the recommended dose reduction of renally cleared antibiotics in patients with impaired renal function is present, with the exception of meropenem.

In vitro Synergistic Activity of Antimicrobial Combinations Against bla KPC and bla NDM-Producing Enterobacterales With bla IMP or mcr Genes

Carbapenemase-producing Enterobacterales have become a severe public health concern because of their rapidly transmissible resistance elements and limited treatment options. The most effective antimicrobial combinations against carbapenemase-producing Enterobacterales are currently unclear. Here, we aimed to assess the therapeutic effects of seven antimicrobial combinations (colistin-meropenem, colistin-tigecycline, colistin-rifampicin, colistin-erythromycin, meropenem-tigecycline, meropenem-rifampicin, and meropenem-tigecycline-colistin) against twenty-four carbapenem-producing Enterobacterales (producing bla_KPC, bla_NDM, coexisting bla_NDM and bla_IMP, and coexisting mcr-1/8/9 and bla_NDM genes) and one carbapenem-susceptible Enterobacterales using the checkerboard assay, time-kill curves, and scanning electron microscopy. None of the combinations were antagonistic. The combination of colistin-rifampicin showed the highest synergistic effect of 76% (19/25), followed by colistin-erythromycin at 60% (15/25), meropenem-rifampicin at 24% (6/25), colistin-meropenem at 20% (5/25), colistin-tigecycline at 20% (5/25), and meropenem-tigecycline at 4% (1/25). The triple antimicrobial combinations of meropenem-tigecycline-colistin had a synergistic effect of 100%. Most double antimicrobial combinations were ineffective on isolates with coexisting bla_NDM and bla_IMP genes. Meropenem with tigecycline showed no synergistic effect on isolates that produced different carbapenemase genes and were highly resistant to meropenem (92% meropenem MIC ≥ 16 mg/mL). Colistin-tigecycline showed no synergistic effect on Escherichia coli producing bla_NDM–1 and Serratia marcescens. Time-kill curves showed that antimicrobial combinations achieved an eradication effect (≥ 3 log₁₀ decreases in colony counts) within 24 h without regrowth, based on 1 × MIC of each drug. The synergistic mechanism of colistin-rifampicin may involve the colistin-mediated disruption of bacterial membranes, leading to severe alterations in their permeability, then causes more rifampicin to enter the cell and induces cell death. In conclusion, the antimicrobial combinations evaluated in this study may facilitate the successful treatment of patients infected with carbapenemase-producing pathogens.

Polymyxin monotherapy versus polymyxin-based combination therapy against carbapenem-resistant Klebsiella pneumoniae: A systematic review and meta-analysis

OBJECTIVES

This meta-analysis was performed to compare polymyxin monotherapy and polymyxin-based combination therapy for carbapenem-resistant Klebsiella pneumoniae (CR-KP) infections.

METHODS

We conducted searches on MEDLINE, Embase and Cochrane Collaborative database for both observational studies and randomised controlled trials (RCTs) comparing polymyxin monotherapy with polymyxin-based combination therapy in patients with CR-KP infection. The primary outcome was mortality. We divided all included studies into several groups according to different combination-combination and different infection types. The odds ratio (OR) and 95% confidence intervals (CI) were calculated for outcome analysis.

RESULTS

Ten studies with 481 patients were included. Polymyxin monotherapy was associated with higher mortality than polymyxin-based combination therapy in treatment of CR-KP bloodstream infections (BSI) (OR 1.93, 95% CI 1.14-3.27, P = 0.01) and ventilator-associated pneumonia (VAP)/hospital-acquired pneumonia (HAP) (OR 3.82, 95% CI 1.15-12.71, P = 0.03). In subgroup analysis of different combinations, mortality was significantly higher with polymyxin monotherapy compared with combination therapy with tigecycline (OR 1.88, 95% CI 1.05-3.37, P = 0.03), or with cabapenem (OR 3.11, 95% CI 1.25-7.74, P = 0.01), but no differences were found in combinations with aminoglycosides (OR 1.29, 95% CI 0.72-2.29, P = 0.38). Three-drug combination therapy including polymyxin was also associated with significant survival benefit (OR 3.86, 95% CI 1.60-9.32, P = 0.003).

CONCLUSIONS

Polymyxin-based combination therapy provides significant survival benefit in treatment of CR-KP, which appears to be more pronounced when a carbapenem or tigecycline is included in the regimen.

In vitro antibacterial activity of ceftazidime/avibactam in combination against planktonic and biofilm carbapenemase-producing Klebsiella pneumoniae isolated from blood

OBJECTIVES

The aim of this study was to report on in vitro tests of antibacterial activity of ceftazidime/avibactam in combination against planktonic or biofilm KPC carbapenemase-producing Klebsiella pneumoniae (KPC-Kp), the rate of KPC-Kp blood isolates in University of Perugia Hospital over a 5-year period, and their antimicrobial susceptibility patterns.

METHODS

The antibacterial activity of ceftazidime/avibactam in combination with other antimicrobials was assessed against planktonic and biofilm bacteria by Etest and checkerboard assay. A retrospective review of laboratory data was performed to evaluate the rate of KPC-Kp from blood samples and their antimicrobial susceptibility patterns.

RESULTS

Between 2014 and 2019, 130/4241 (3.1%) KPC-Kp were identified from blood cultures. Their rate increased from 2.3% in 2014-2015 to 4.5% over the last 3 years. Overall, 4.6% (6/130) of KPC-Kp isolates were susceptible to meropenem, 65.4% (85/130) to colistin, 65.1% (84/129) to tigecycline, 34.6% (45/130) to amikacin, 36.2% (42/116) to gentamicin, 40.2% (39/97) to fosfomycin and 91.5% (65/71) to ceftazidime/avibactam. Five of six ceftazidime/avibactam-resistant KPC-Kp were isolated from patients not treated with ceftazidime/avibactam. Synergism was detected both by Etest and checkerboard assay for the combination of ceftazidime/avibactam plus meropenem against planktonic isolates, whilst lower bactericidal activity was observed in biofilm KPC-Kp isolates.

CONCLUSIONS

Our in vitro data suggest that the combination of ceftazidime/avibactam plus meropenem has a synergistic antibacterial activity against planktonic bacteria, whilst a lower activity was detected against biofilm, suggesting worse clinical outcomes whenever biofilm infections are present. Further analyses are required to confirm these results before extending them to clinical practice.

Carbapenem-sparing strategy: carbapenemase, treatment, and stewardship

PURPOSE OF REVIEW

describing the current role of carbapenems and carbapenem-sparing strategies in the setting of antimicrobial stewardship programs.

RECENT FINDINGS

sparing carbapenems with other drugs appears to be an interesting perspective for a variety of reasons in the current context of the multidrug-resistant (MDR) pandemic. Specific algorithms should also be precisely investigated to define better how to spare carbapenems within empiric and targeted regimens, with combination treatment or monotherapies, aiming at the best use of the new drugs and improving de-escalation as soon as possible for most of the patients.

SUMMARY

stewardship programs may be useful in reducing probable misuse and overuse of antibiotics, which has probably contributed to the emergence of carbapenem-resistant bacteria worldwide. The proposal of carbapenem-sparing strategies has then generated substantial scientific debate and, overall, the concept of sparing these drugs is well advocated together with judicious use of novel drugs, appropriate measures of infection control and prevention as well as in stewardship programs to curb the spread of MDR and XDR-strains in healthcare facilities.

Analysis of Paradoxical Efficacy of Carbapenems against Carbapenemase-Producing Escherichia coli in a Murine Model of Lethal Peritonitis

The clinical benefit of carbapenems against carbapenemase-producing Enterobacteriaceae (CPE) remains in question. MICs of imipenem (IMP) and ertapenem (ERT) against isogenic derivatives of the wild-type strain Escherichia coli CFT073 producing KPC-3, OXA-48, or NDM-1 were 0.25, 2, 16, and 64 mg/liter for IMP and 0.008, 0.5, 8, and 64 mg/liter for ERT, respectively. Swiss ICR-strain mice with peritonitis were treated for 24 h with IMP or ERT. Despite a limited duration of time during which free antibiotic concentrations were above the MIC (down to 0% for the NDM-1-producing strain), IMP and ERT significantly reduced bacterial counts in spleen and peritoneal fluid at 24 h (P < 0.005) and prevented mortality. Several possible explanations were investigated. Addition of 4% albumin or 50% normal human serum did not modify IMP activity. Bacterial fitness of resistant strains was not altered and virulence did not decrease with resistance. In the presence of subinhibitory concentrations of ERT, growth rates of OXA-48, KPC-3, and NDM-1 strains were significantly decreased and filamentation of the NDM-1 strain was observed. The expression of bla _NDM-1 was not decreased in vivo compared to in vitro No zinc depletion was observed in infected mice compared with Mueller-Hinton broth. In conclusion, a paradoxical in vivo efficacy of IMP and ERT against highly resistant carbapenemase-producing E. coli was confirmed. Alternative mechanisms of antibacterial effects of subinhibitory concentrations of carbapenems may be involved to explain in vivo activity. These results are in agreement with a potential clinical benefit of carbapenems to treat CPE infections, despite high carbapenem MICs.

Infections Due to Carbapenem-Resistant Bacteria in Patients With Hematologic Malignancies

In developed countries, hematological malignancies (HM) account for 8 to 10% of cancers diagnosed annually and one-third of patients with HM (HMP) are expected to die from their disease. The former wide spectrum “magic bullet,” imipenem, has been ousted by the emergence of carbapenem resistant (CR) pathogens. In endemic areas, infections with CR-bacteria occur in vulnerable patients, notably in HMP, who suffer from high mortality related to infectious complications. In this work, we reviewed epidemiologic and clinical factors associated with CR-infections in adult HMP and data on CR-related mortality and antibiotic treatments in this population. We found that resistance profile of strains involved in HMP infections, mainly bacteremia, reflect local epidemiology. Significant risk factors for infections with CR-bacteria include sex male, age around 50 years old, acute leukemia, selvage chemotherapy, neutropenia, and digestive colonization by CR-bacteria. Mortality rate is high in HMP infected with CR-Enterobacteriaceae, more particularly in case of acute myeloid leukemia and unresolved neutropenia, due to inappropriate empiric management and delayed administration of targeted antibiotics, such as tigecycline, colistin, or new associations of active drugs. Thus, we developed an algorithm for clinicians, assessing the incremental risk for CR-bacterial infection occurrence and mortality in febrile HMP, to guide decisions related to empirical therapeutic strategies.

How to manage KPC infections

Carbapenemase-producing Enterobacteriaceae represent an increasing global threat worldwide and Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has become one of the most important contemporary pathogens, especially in endemic areas. Risk stratification and rapid diagnostics laboratory workflows are of paramount importance and indication for therapy of KPC-KP infection must be individualized according to the baseline characteristics of the patient and severity of infection. The optimal treatment of infection because of KPC-KP organisms is uncertain and antibiotic options are limited. The knowledge of the patient's pathophysiology, infection site, and application of the pharmacokinetic/pharmacodynamic principles on the basis of minimum inhibitory concentration (MIC) has progressively gained major relevance. Combination therapies including high-dose meropenem, colistin, fosfomycin, tigecycline, and aminoglycosides are widely used, with suboptimal results. In the past few years, new antimicrobials targeting KPC-KP have been developed and are now at various stages of clinical research. However, their optimal use should be guaranteed in the long term for delaying, as much as possible, the emergence of resistance. Strict infection control measures remain necessary. The aim of this review is to discuss the challenges in the management and treatment of patients with infections because KPC-KP and provide an expert opinion.

Precision medicine for the diagnosis and treatment of carbapenem-resistant Enterobacterales: time to think from a different perspective

INTRODUCTION

Carbapenem-resistant Enterobacterales (CRE) represent a global public health problem. Precision medicine (PM) is a multicomponent medical approach that should be used to individualize the management of patients infected with CRE.

AREAS COVERED

Here, we differentiate carbapenem-producing CRE (CP-CRE) from non-CP-CRE and the importance of this distinction in clinical practice. The current phenotypic CRE-case definition and its implications are also discussed. Additionally, we summarize data regarding phenotypic and molecular diagnostic tools and available antibiotics. In order to review the most relevant data, a comprehensive literature search of peer-reviewed articles in PubMed and abstracts presented at high-impact conferences was performed.

EXPERT OPINION

PM in CRE infections entails a multi-step process that includes applying the current phenotypic definition, utilization of the right phenotypic or molecular testing methods, and thorough evaluation of risk factors, source of infection, and comorbidities. A powerful armamentarium is available to treat CRE infections, including recently approved agents. Randomized controlled trials targeting specific pathogens instead of site of infections may be appropriate to fill in the current gaps. In light of the diverse enzymology behind CP-CRE, PM should be employed to provide the best therapy based on the underlying resistance mechanism.

Is Meropenem as a Monotherapy Truly Incompetent for Meropenem-Nonsusceptible Bacterial Strains? A Pharmacokinetic/Pharmacodynamic Modeling With Monte Carlo Simulation

Infections due to meropenem-nonsusceptible bacterial strains (MNBSs) with meropenem minimum inhibitory concentrations (MICs) ≥ 16 mg/L have become an urgent problem. Currently, the optimal treatment strategy for these cases remains uncertain due to some limitations of currently available mono- and combination therapy regimens. Meropenem monotherapy using a high dose of 2 g every 8 h (q 8 h) and a 3-h traditional simple prolonged-infusion (TSPI) has proven to be helpful for the treatment of infections due to MNBSs with MICs of 4–8 mg/L but is limited for cases with higher MICs of ≥16 mg/L. This study demonstrated that optimized two-step-administration therapy (OTAT, i.e., a new administration model of i.v. bolus plus prolonged infusion) for meropenem, even in monotherapy, can resolve this problem and was thus an important approach of suppressing such highly resistant bacterial isolates. Herein, a pharmacokinetic (PK)/pharmacodynamic (PD) modeling with Monte Carlo simulation was performed to calculate the probabilities of target attainment (PTAs) and the cumulative fractions of response (CFRs) provided by dosage regimens and 39 OTAT regimens in five dosing models targeting eight highly resistant bacterial species with meropenem MICs ≥ 16 mg/L, including Acinetobacter baumannii, Acinetobacter spp., Enterococcus faecalis, Enterococcus faecium, Pseudomonas aeruginosa, Staphylococcus epidermidis, Staphylococcus haemolyticus, and Stenotrophomonas maltophilia, were designed and evaluated. The data indicated that meropenem monotherapy administered at a high dose of 2 g q 8 h and as an OTAT achieved a PTA of ≥90% for isolates with an MIC of up to 128 mg/L and a CFR of ≥90% for all of the targeted pathogen populations when 50% f T > MIC (50% of the dosing interval during which free drug concentrations remain above the MIC) is chosen as the PD target, with Enterococcus faecalis being the sole exception. Even though 50% f T > 5 × MIC is chosen as the PD target, the aforementioned dosage regimen still reached a PTA of ≥90% for isolates with an MIC of up to 32 mg/L and a CFR of ≥90% for Acinetobacter spp., Pseudomonas aeruginosa, and Klebsiella pneumoniae populations. In conclusion, meropenem monotherapy displays potential competency for infections due to such highly resistant bacterial isolates provided that it is administered as a reasonable OTAT but not as the currently widely recommended TSPI.

Carbapenem-Resistant Klebsiella pneumoniae: Microbiology Key Points for Clinical Practice

Carbapenemase–producing Klebsiella pneumoniae strains (Cp-Kpn) represent a challenge for clinical practitioners due to their increasing prevalence in hospital settings and antibiotic resistance. Clinical practitioners are often overwhelmed by the extensive list of publications regarding Cp-Kpn infections, treatment, characteristics, identification, and diagnosis. In this perspective article, we provide key points for clinical practitioners to consider for improved patient management including identification of risk factors and strategies for treatment. Additionally, we also discuss genetic underpinnings of antibiotic resistance, implementation of an antimicrobial stewardship program (ASP), and use of automated systems for detection of Cp-Kpn. Collectively, implementation of such key points would enhance clinical practices through providing practical knowledge to health professionals worldwide.

Use of meropenem in treating carbapenem-resistant Enterobacteriaceae infections

Introduction: The epidemiology of carbapenem-resistant Enterobacterales (CRE) is increasingly worldwide. Production of carbapenemases is the most common and efficient mechanism of carbapenem resistance, and could theoretically be overcome by optimizing the pharmacokinetic/pharmacodynamic (PK/PD) behavior of meropenem. Areas covered: This article overviews the available literature concerning the potential role that meropenem may still have in the treatment carbapenem-resistant Enterobacteriaceae infections. Clinical studies published in English language until June 2019 were searched on PubMed database. Expert commentary: High-dose continuous infusion meropenem-based combination regimens could still represent a valuable option for treating CRE infections in specific circumstances. Knowledge of the local prevalent mechanisms of carbapenem resistance, of patient clinical severity, of the site of infection, of an accurate minimum inhibitory concentration (MIC) value, coupled with the possibility of carrying-out a real-time therapeutic drug monitoring (TDM)-based PK/PD optimization of drug exposure must all be considered as fundamental for properly pursuing this goal.

Clinical and epidemiological characteristics of KPC-producing Klebsiella pneumoniae from bloodstream infections in a tertiary referral center in Italy

Background

Bloodstream infections (BSI) due to Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-Kp) have become an important problem and they are associated with a high mortality rate. The aim of our study was to evaluate the clinical and epidemiological characteristics of KPC-Kp from BSIs.

Methods

In this retrospective cohort study, conducted in a tertiary referral center in Italy, 112 patients with KPC-Kp BSIs diagnosed between February 2011 and December 2015 were identified. We evaluated the mortality at 30 days from the first positive blood culture. Survivor and non-survivor subgroups were compared to identify predictors of mortality.

Results

The overall crude mortality was 35%. APACHE II score ≥ 15, septic shock at BSI onset, immunosuppressive therapy during the 30 days before the BSI onset, and the lack of a combination therapy with at least 2 active drugs emerged as independent predictors of mortality. Excluding patients with inadequate therapy, the mortality decreased to 25% while an APACHE II score ≥ 15 and the presence of septic shock remained independently associated with a negative outcome.

Two different pulsotypes were identified: pulsotype A belonged to ST512 and carried KPC-3 and pulsotype B belonged to ST307 and carried KPC-2.

Conclusions

This study confirmed a high mortality rate of KPC-Kp BSIs. The outcome is heavily influenced by the patient’s clinical conditions. A therapeutic approach including a combination with at least two active drugs in vitro can improve the prognosis, unless patients received an appropriate therapy.

Treatment of Infections Due to MDR Gram-Negative Bacteria

The treatment of multidrug-resistant Gram-negative bacteria (MDR-GNB) infections in critically ill patients presents many challenges. Since an effective treatment should be administered as soon as possible, resistance to many antimicrobial classes almost invariably reduces the probability of adequate empirical coverage, with possible unfavorable consequences. In this light, readily available patient's medical history and updated information about the local microbiological epidemiology remain critical for defining the baseline risk of MDR-GNB infections and firmly guiding empirical treatment choices, with the aim of avoiding both undertreatment and overtreatment. Rapid diagnostics and efficient laboratory workflows are also of paramount importance both for anticipating diagnosis and for rapidly narrowing the antimicrobial spectrum, with de-escalation purposes and in line with antimicrobial stewardship principles. Carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii are being reported with increasing frequencies worldwide, although with important variability across regions, hospitals and even single wards. In the past few years, new treatment options, such as ceftazidime/avibactam, meropenem/vaborbactam, ceftolozane/tazobactam, plazomicin, and eravacycline have become available, and others will become soon, which have provided some much-awaited resources for effectively counteracting severe infections due to these organisms. However, their optimal use should be guaranteed in the long term, for delaying as much as possible the emergence and diffusion of resistance to novel agents. Despite important progresses, pharmacokinetic/pharmacodynamic optimization of dosages and treatment duration in critically ill patients has still some areas of uncertainty requiring further study, that should take into account also resistance selection as a major endpoint. Treatment of severe MDR-GNB infections in critically ill patients in the near future will require an expert and complex clinical reasoning, of course taking into account the peculiar characteristics of the target population, but also the need for adequate empirical coverage and the more and more specific enzyme-level activity of novel antimicrobials with respect to the different resistance mechanisms of MDR-GNB.

Dose Optimization of Colistin Combinations against Carbapenem-Resistant Acinetobacter baumannii from Patients with Hospital-Acquired Pneumonia in China by Using an In Vitro Pharmacokinetic/Pharmacodynamic Model

Colistin-based combination therapy has become an important strategy to combat the carbapenem-resistant Acinetobacter baumannii (CRAB). However, the optimal dosage regimen selection for the combination with maximum efficacy is challenging. Checkerboard assay was employed to evaluate the synergy of colistin in combination with meropenem, rifampin, fosfomycin, and minocycline against nine carbapenem-resistant A. baumannii isolates (MIC of meropenem [MIC_MEM], ≥32 mg/liter) isolated from Chinese hospital-acquired pneumonia (HAP) patients. A static time-kill assay, in vitro dynamic pharmacokinetic/pharmacodynamic (PK/PD) model, and semimechanistic PK/PD modeling were conducted to predict and validate the synergistic effect of the most efficacious combination. Both checkerboard and static time-kill assays demonstrated the superior synergistic effect of the colistin-meropenem combination against all CRAB isolates. In the in vitro PK/PD model, the dosage regimen of 2 g meropenem daily via 3-h infusion combined with steady-state 1 mg/liter colistin effectively suppressed the bacterial growth at 24 h with a 2-log₁₀ decrease, compared with the initial inocula against two CRAB isolates. The semimechanistic PK/PD model predicted that more than 2 mg/liter colistin combined with meropenem (2 g, 3-h infusion) was required to achieve the killing below the limit of detection (<LOD; i.e., 1 log₁₀CFU/ml) at 24 h with an MIC_MEM of ≥32 mg/liter. Colistin combined with meropenem exerted synergistic killing against CRAB even with an MIC_MEM of ≥32 mg/liter and MIC of colistin (MIC_CST) of ≤1 mg/liter. However, it is predicted that a higher concentration of colistin combined with meropenem was crucial to kill bacteria to <LOD. Our study provides important PK/PD information for optimization of the colistin and meropenem combination against CRAB.

Current and emerging pharmacotherapy for the treatment of infections following open-heart surgery

INTRODUCTION

Patients undergoing open-heart surgery may suffer from postoperative complications, including severe infections. Antimicrobials to treat infectious complications in this population should be selected thoughtfully, taking into account three different and fundamental issues: (i) the site of infection; (ii) the suspected or proven causative agent and its susceptibility pattern; and (iii) the risk of suboptimal pharmacokinetic characteristics and potential toxicity of the chosen drug/s.

AREAS COVERED

The present narrative review summarizes the current and future antimicrobial options for the treatment of infections developing after open-heart surgery.

EXPERT OPINION

The pharmacological treatment of infections developing in cardiac surgery patients poses peculiar challenges, including the need for an active empirical therapy for severe events such as bloodstream infections, deep sternal wound infections, or early-onset postoperative prosthetic endocarditis. In addition, the risk for multidrug-resistant pathogens should also be taken into account in endemic areas. A multidisciplinary evaluation on a patient-by-patient basis, deeply involving infectious diseases specialists and cardiothoracic surgeons, remains essential for appropriately balancing both short-term and long-term risks and benefits of any possible surgical reintervention in combination with adequate pharmacotherapy.

Infections Caused by Carbapenem-Resistant Enterobacteriaceae: An Update on Therapeutic Options

Carbapenems are considered as last-resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. With the increasing use of carbapenems in clinical practice, the emergence of carbapenem-resistant pathogens now poses a great threat to human health. Currently, antibiotic options for the treatment of carbapenem-resistant Enterobacteriaceae (CRE) are very limited, with polymyxins, tigecycline, fosfomycin, and aminoglycosides as the mainstays of therapy. The need for new and effective anti-CRE therapies is urgent. Here, we describe the current understanding of issues related to CRE and review combination therapeutic strategies for CRE infections, including high-dose tigecycline, high-dose prolonged-infusion of carbapenem, and double carbapenem therapy. We also review the newly available antibiotics which have potential in the future treatment of CRE infections: ceftazidime/avibactam, which is active against KPC and OXA-48 producers; meropenem/vaborbactam, which is active against KPC producers; plazomicin, which is a next-generation aminoglycoside with in vitro activity against CRE; and eravacycline, which is a tetracycline class antibacterial with in vitro activity against CRE. Although direct evidence for CRE treatment is still lacking and the development of resistance is a concern, these new antibiotics provide additional therapeutic options for CRE infections. Finally, we review other potential anti-CRE antibiotics in development: imipenem/relebactam and cefiderocol. Currently, high-dose and combination strategies that may include the new β-lactam/β-lactamase inhibitors should be considered in severe CRE infections to maximize treatment success. In the future, when more treatment options are available, therapy for CRE infections should be individualized and based on molecular phenotypes of resistance, susceptibility profiles, disease severity, and patient characteristics. More high-quality studies are needed to guide effective treatment for infections caused by CRE.

Hypoalbuminemia as a predictor of acute kidney injury during colistin treatment

This study aimed to assess the predictors of acute kidney injury (AKI) during colistin therapy in a cohort of patients with bloodstream infections (BSI) due to colistin-susceptible Gram-negative bacteria, focusing on the role of serum albumin levels. The study consisted of two parts: (1) a multicentre retrospective clinical study to assess the predictors of AKI during colistin therapy, defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria; and (2) bioinformatic and biochemical characterization of the possible interaction between human serum albumin and colistin. Among the 170 patients included in the study, 71 (42%), 35 (21%), and 11 (6%) developed KDIGO stage 1 (K1-AKI), KDIGO stage 2 (K2-AKI), and KDIGO stage 3 (K3-AKI), respectively. In multivariable analyses, serum albumin <2.5 g/dL was independently associated with K1-AKI (subdistribution hazard ratio [sHR] 1.85, 95% confidence interval [CI] 1.17-2.93, p = 0.009) and K2-AKI (sHR 2.37, 95% CI 1.15-4.87, p = 0.019). Bioinformatic and biochemical analyses provided additional information nurturing the discussion on how hypoalbuminemia favors development of AKI during colistin therapy. In conclusion, severe hypoalbuminemia independently predicted AKI during colistin therapy in a large cohort of patients with BSI due to colistin-susceptible Gram-negative bacteria. Further study is needed to clarify the underlying causal pathways.

Wagenlehner F, Zimmer KP, Chakraborty T. Treatment Options for Carbapenem- Resistant Gram-Negative Infections

BACKGROUND

Rates of colonization and infection with carbapenem-resistant Gram-negative pathogens are on the rise, particularly in southeastern European countries, and this is increasingly true in Germany as well. The organisms in question include enterobacteriaceae such as Klebsiella pneumoniae and Escherichia coli and non-fermenting bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii. As the carbapenems have been the gold standard to date for the systemic treatment of serious infections with Gram-negative bacteria, carbapenem resistance presents new and difficult challenges in therapeutic decision-making, particularly because of the high frequency of coresistance.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed and on other applicable literature.

RESULTS

Multiresistant Gram-negative (MRGN) pathogens are classified in Germany according to their resistance to four different classes of antibiotics; fluoroquinolones, piperacillin, third-generation cephalosporins, and carbapenems. Quadruple MRGN pathogens are resistant to all four groups, triple MRGN pathogens to three of them. There are a number of therapeutic alternatives to carbapenems that can be applied with the aid of sensitive microbiological and/or molecular genetic testing. The following antibiotics are often the only ones that can be used to treat quadruple MRGN pathogens: colistin, aminoglycosides, tigecycline, fosfomycin, ceftazidime/avibactam, and ceftolozan/tazobactam. Carbapenems, too, may still be an option in certain situations. There is also evidence that combinations of antibiotics against which the pathogen is resistant individually can some- times be a valid treatment option; these include combinations of colistin with one or two carbapenems.

CONCLUSION

The treatment of severe infection with carbapenem-resistant pathogens should be individualized and carried out in an interdisciplinary framework, in consideration of antibiotic pharmacokinetics and pharmacodynamics in each case. The treat- ment options are based on evidence from in vitro studies, retrospective studies, and case series, which must be interpreted with caution. Randomized clinical trials are needed to test each of the various combined approaches.

Pharmacokinetic/pharmacodynamic parameters for treatment optimization of infection due to antibiotic resistant bacteria: a summary for practical purposes in children and adults

In the last years, there has been a tremendous increase in the incidence of bacterial infections due to resistant strains, especially multi-drug resistant Gram-negative bacilli. In Europe, a north to south and a west to east gradient was noticed, with more than one third of the K. pneumonia isolates being resistant to carbapenems in few countries. New antibiotics are lacking and, as a consequence, pharmacokinetic/pharmacodynamic parameters, normalized to pathogen minimal inhibitory concentration, are used with increased frequency to treat infections due to difficult-to-treat pathogens. These parameters are available at least for the adult population, but sparse in many different publications. This review wants to provide a comprehensive and 'easy to read' text for everyday practice, briefly summarizing the presently available knowledge on pharmacokinetic/pharmacodynamic parameters (normalized for minimal inhibitory concentration values) of different class drugs, that can be applied for an effective antibacterial treatment infections due to antibiotic-resistant pathogens.

Population Pharmacokinetics of High-Dose Continuous-Infusion Meropenem and Considerations for Use in the Treatment of Infections Due to KPC-Producing Klebsiella pneumoniae

We assessed the population pharmacokinetics of high-dose continuous-infusion (HDCI) meropenem in a cohort of patients with Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (KPC-Kp) infections. Monte Carlo simulations were used to define the permissible HDCI meropenem regimens that could be safely considered for the treatment of KPC-Kp infections due to meropenem-resistant strains. Permissible doses were arbitrarily defined as those associated with a ≤10% to 15% likelihood of meropenem steady-state concentrations (C_ss) of >100 mg/liter. Probabilities of target attainment (PTA) of four incremental pharmacodynamic determinants for meropenem efficacy (100% T_>1×MIC, 100% T_>2×MIC, 100% T_>3×MIC, and 100% T_>4×MIC, where "T_>MIC" represents the time during which the plasma concentration of this time-dependent antibacterial agent is maintained above the MIC for the pathogen) in relation to different classes of renal function were calculated. The cumulative fractions of response (CFR) for the permissible HDCI meropenem regimens were calculated against the MIC distribution of the KPC-Kp clinical isolates that were collected routinely at our University Hospital between 2013 and 2016 (n = 169). Ninety-seven meropenem C_ss were included in the analysis. The final model included creatinine clearance (CrCL) as a covariate and explained 94% of the population variability. Monte Carlo simulations based on licensed dosages of up to 6 g/day predicted an acceptable PTA (>80%) of 100% T_>1×MIC against KPC-Kp with a meropenem MIC of ≤32 mg/liter in patients with a CrCL level of <130 ml/min. Dosages of 8 g/day were needed for achieving the same target in patients with CrCL at levels of 130 to 200 ml/min. In dealing with pathogens with a meropenem MIC of 64 mg/liter, HDCI regimens using meropenem at higher than licensed levels should be considered. In these cases, real-time therapeutic drug monitoring could be a useful adjunct for optimized care. The predicted CFR were >75% in all of the classes of renal function.

Management of KPC-producing Klebsiella pneumoniae infections

BACKGROUND

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has become one of the most important contemporary pathogens, especially in endemic areas.

AIMS

To provide practical suggestion for physicians dealing with the management of KPC-KP infections in critically ill patients, based on expert opinions.

SOURCES

PubMed search for relevant publications related to the management of KPC-KP infections.

CONTENTS

A panel of experts developed a list of 12 questions to be addressed. In view of the current lack of high-level evidence, they were asked to provide answers on the bases of their knowledge and experience in the field. The panel identified several key aspects to be addressed when dealing with KPC-KP in critically ill patients (preventing colonization in the patient, preventing infection in the colonized patient and colonization of his or her contacts, reducing mortality in the infected patient by rapidly diagnosing the causative agent and promptly adopting the best therapeutic strategy) and provided related suggestions that were based on the available observational literature and the experience of panel members.

IMPLICATIONS

Diagnostic technologies could speed up the diagnosis of KPC-KP infections. Combination treatment should be preferred to monotherapy in cases of severe infections. For non-critically ill patients without severe infections, results from randomized clinical trials are needed for ultimately weighing benefits and costs of using combinations rather than monotherapy. Multifaceted infection control interventions are needed to decrease the rates of colonization and cross-transmission of KPC-KP.

Mortality Associated with Bacteremia Due to Colistin-Resistant Klebsiella pneumoniae with High-Level Meropenem Resistance: Importance of Combination Therapy without Colistin and Carbapenems

Combination therapy including colistin and a carbapenem has been found to be associated with lower mortality in the treatment of bloodstream infections (BSI) due to KPC-producing Klebsiella pneumoniae when the isolates show a meropenem or imipenem MIC of <16 mg/liter. However, the optimal treatment of BSI caused by colistin- and high-level carbapenem-resistant KPC-producing K. pneumoniae is unknown. A prospective cohort study including episodes of bacteremia caused by colistin-resistant and high-level meropenem-resistant (MIC ≥ 64 mg/liter) KPC-producing K. pneumoniae diagnosed from July 2012 to February 2016 was performed. The impact of combination therapy on crude 30-day mortality was analyzed by Cox regression using a propensity score as a covariate to control for indication bias and in an inverse probability of treatment weighting (IPTW) cohort. The study sample comprised 104 patients, of which 32 (30.8%) received targeted monotherapy and 72 (69.2%) received targeted combination therapy; none of them received either colistin or a carbapenem. The 30-day crude mortality rate was 30.8% (43.8% in patients treated with monotherapy and 25% in patients receiving combination therapy). In the Cox regression analysis, 30-day mortality was independently associated with septic shock at BSI onset (hazard ratio [HR], 6.03; 95% confidence interval [CI], 1.65 to 21.9; P = 0.006) and admission to the critical care unit (HR, 2.87; 95% CI, 0.99 to 8.27; P = 0.05). Targeted combination therapy was associated with lower mortality only in patients with septic shock (HR, 0.14; 95% CI, 0.03 to 0.67; P = 0.01). These results were confirmed in the Cox regression analysis of the IPTW cohort. Combination therapy is associated with reduced mortality in patients with bacteremia due to colistin-resistant KPC-producing K. pneumoniae with high-level carbapenem resistance in patients with septic shock.

Therapeutic options for carbapenem-resistant Enterobacteriaceae infections

In recent years, carbapenem resistance among Enterobacteriaceae has dramatically increased and represents an important threat to global health. The optimal therapeutic management of carbapenem-resistant Enterobacteriaceae (CRE) infections has not been established, because to date, no clinical trials have been performed with this objective. We aimed to summarize in the present review data provided by previous observational clinical studies that have investigated the impact of different treatment strategies on the outcome of CRE infections. Most of these studies reported that combination therapy with 2 or more drugs is superior to monotherapy in providing a survival benefit. The use of carbapenems in association with other active drugs is likely ineffective for CRE isolates with carbapenem Minimum Inhibitory Concentrations (MICs) >8 mg/l. The effectiveness of further therapeutic options for the treatment of extensively or pan-drug-resistant Enterobacteriaceae infections has been reported in vivo and in vitro, although few cases/case series have been reported. Novel antimicrobials that are effective against CRE are urgently needed.