Amoxicillin-clavulanate Breakpoints Against Enterobacterales: Rationale for Revision by the Clinical and Laboratory Standards Institute

Amoxicillin-clavulanate (AMC) is among the most frequently prescribed antibiotics globally. It has broad antibacterial activity against gram-positive, gram-negative, and anaerobic bacteria, and has been utilized to treat infections caused by a broad range of pathogens. AMC breakpoints against Enterobacterales were initially set in the 1980s but since then increases in antibiotic resistance, advances in pharmacokinetic (PK)/pharmacodynamic (PD) analyses, and publication of additional clinical data prompted a reassessment by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing. Based on this contemporary reappraisal, the CLSI retained the Enterobacterales breakpoints but revised comments regarding dosing associated with use of the AMC breakpoints in the 2022 supplement of M100. This viewpoint provides insight into the CLSI breakpoint reevaluation process and summarizes the data and rationale used to support these revisions to the AMC Enterobacterales breakpoint.

Assessment of antibiotic release and antibacterial efficacy from pendant glutathione hydrogels using ex vivo porcine skin

Acute bacterial skin and skin structure infections (ABSSSIs) confer a substantial burden on the healthcare system. Local antibiotic delivery systems can provide controlled drug release directly to the site of infection to maximize efficacy and minimize systemic toxicity. The purpose of this study was to examine the antibacterial activity of antibiotic-loaded glutathione-conjugated poly(ethylene glycol) hydrogels (GSH-PEG) against ABSSSIs utilizing an ex vivo porcine dermal explant model. Vancomycin- or meropenem-loaded GSH-PEG hydrogels at 3 different dose levels were loaded over 1 h. Drug release was monitored in vitro under submerged conditions, by the Franz cell diffusion method, and ex vivo utilizing a porcine dermis model. Antibacterial activity was assessed ex vivo on porcine dermis explants inoculated with Staphylococcus aureus or Pseudomonas aeruginosa isolates treated with vancomycin- or meropenem-loaded GSH-PEG hydrogels, respectively. Histological assessment of the explants was conducted to evaluate tissue integrity and viability in the context of the experimental conditions. A dose-dependent release was observed from vancomycin and meropenem hydrogels, with in vitro Franz cell diffusion data closely representing ex vivo vancomycin release, but not high dose meropenem release. High dose vancomycin-loaded hydrogels resulted in a >3 log10 clearance against all S. aureus isolates at 48 h. High dose meropenem-loaded hydrogels achieved 6.5, 4, and 2 log10 reductions in CFU/ml against susceptible, intermediate, and resistant P. aeruginosa isolates, respectively. Our findings demonstrate the potential application of GSH-PEG hydrogels for flexible, local antibiotic delivery against bacterial skin infections.

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.

Pharmacokinetics and dialytic clearance of baricitinib during in vivo continuous venovenous haemodialysis in a patient with COVID-19

OBJECTIVES

To date, there are no published pharmacokinetic (PK) data for baricitinib in critically ill patients requiring continuous renal replacement therapy. This paper describes in detail the plasma PK and dialytic clearance of baricitinib in a patient infected with coronavirus disease 2019 (COVID-19) requiring continuous renal replacement therapy in order to suggest dosing strategies in this population.

METHODS

Baricitinib 2 mg daily was used for the treatment of COVID-19 in a critically ill patient on continuous venovenous haemodialysis (CVVHD). Prefiltration plasma drug concentrations of baricitinib were measured at hours 1, 2, 12, and 24 after drug administration. Postfiltration and ultrafiltrate concentrations were collected at hour 24.

RESULTS

Plasma PK parameters of baricitinib in this patient were as follows: maximum plasma concentration (Cmax), 20.98 ng/mL; minimum plasma concentration (Cmin), 9.84 ng/mL; half-life (t1/2), 23.85 h; apparent volume of distribution at the steady state (Vss), 99.42 L; total clearance at the steady state (CLss), 2.89 L/h; and area under the concentration-time curve (AUC0-∞), 692.14 ng · h/mL. The saturation coefficient for baricitinib at 24 h after administration was 0.607. The transmembrane clearance of baricitinib by CVVHD running at a flow rate of 2 L/h was 1.21 L/h, representing 41.9% of the total clearance of baricitinib.

CONCLUSIONS

In a critically ill COVID-19 patient on CVVHD, a 2-mg dose of baricitinib achieves a Cmax comparable with healthy subjects, but total clearance was reduced to about 20%. Larger studies exploring multiple patients and dialysis modes are needed to determine the optimal dosing strategy for baricitinib in this patient population.

Rapid Diagnostic Test Value and Implementation in Antimicrobial Stewardship Across Low-to-Middle and High-Income Countries: A Mixed-Methods Review

Despite technological advancements in infectious disease rapid diagnostic tests (RDTs) and use to direct therapy at the per-patient level, RDT utilisation in antimicrobial stewardship programmes (ASPs) is variable across low-to-middle income and high-income countries. Key insights from a panel of seven infectious disease experts from Colombia, Japan, Nigeria, Thailand, the UK, and the USA, combined with evidence from a literature review, were used to assess the value of RDTs in ASPs. From this, a value framework is proposed which aims to define the benefits of RDT use in ASPs, separate from per-patient benefits. Expert insights highlight that, to realise the value of RDTs within ASPs, effective implementation is key; actionable advice for choosing an RDT is proposed. Experts advocate the inclusion of RDTs in the World Health Organization Model List of essential in vitro diagnostics and in iterative development of national action plans.

Multicenter Evaluation of an MIC-Based Aztreonam and Ceftazidime-Avibactam Broth Disk Elution Test

Due to limited therapeutic options, there is a clinical need to assess the in vitro activity of the combination of aztreonam (ATM) and ceftazidime-avibactam (CZA) to guide the therapeutic management of multidrug-resistant (MDR) Gram-negative organism infections. We set out to develop a practical MIC-based broth disk elution (BDE) method to determine the in vitro activity of the combination ATM-CZA using readily available supplies and compare it to reference broth microdilution (BMD). For the BDE method, a 30-μg ATM disk, a 30/20-μg CZA disk, both disks in combination, and no disks were added to 4 separate 5-mL cation-adjusted Mueller-Hinton broth (CA-MHB) tubes, using various manufacturers. Three testing sites performed both BDE and reference BMD testing of bacterial isolates in parallel from a single 0.5 McFarland standard inoculum and after overnight incubation, assessed them for growth (not susceptible) or no growth (susceptible) at a final concentration of 6/6/4 μg/mL ATM-CZA. During the first phase, the precision and accuracy of the BDE were analyzed by testing 61 Enterobacterales isolates at all sites. This testing yielded 98.3% precision between sites, with 98.3% categorical agreement and 1.8% major errors (ME). During the second phase, at each site, we evaluated unique, clinical isolates of metallo-β-lactamase (MBL)-producing Enterobacterales (n = 75), carbapenem-resistant Pseudomonas aeruginosa (n = 25), Stenotrophomonas maltophilia (n = 46), and Myroides sp. (n = 1). This testing resulted in 97.9% categorical agreement, with 2.4% ME. Different results were observed for different disk and CA-MHB manufacturers, requiring a supplemental ATM-CZA-not-susceptible quality control organism to ensure the accuracy of results. The BDE is a precise and effective methodology for determining susceptibility to the combination ATM-CZA.

Comparison of thrombotic and clinical outcomes in SARS-CoV-2-pneumonia versus other viral pneumonia in an urban academic medical center

BACKGROUND

Infection with viral pneumonia (PNA) is known to offset the coagulation cascade. Recent studies assessing novel SARS-CoV-2 infection observed a high frequency of systemic thrombotic events resulting in ambiguity if severity of infection or specific viral strain drive thrombosis and worsen clinical outcomes. Furthermore, limited data exists addressing SARS-CoV-2 in underrepresented patient populations.

OBJECTIVES

Assess clinical outcomes events and death in patients diagnosed with SARS-CoV-2 pneumonia compared to patients with other types of viral pneumonia.

METHODS

Retrospective cohort study evaluated electronic medical records in adult patients admitted to University of Illinois Hospital and Health Sciences System (UIHHSS) with primary diagnosis of SARS-CoV-2 PNA or other viral (H1N1 or H3N2) PNA between 10/01/2017 and 09/01/2020. Primary composite outcome was the following event incidence rates: death, ICU admission, infection, thrombotic complications, mechanical ventilation, renal replacement therapy, and major bleeding.

RESULTS

Of 257 patient records, 199 and 58 patients had SARS-CoV-2 PNA and other viral PNA, respectively. There was no difference in primary composite outcome. Thrombotic events (n = 6, 3%) occurred solely in SARS-CoV-2 PNA patients in the ICU. A significantly higher incidence of renal replacement therapy (8.5% vs 0%, p=0.016) and mortality (15.6% vs 3.4%, p=0.048) occurred in the SARS-CoV-2 PNA group. Multivariable logistic regression analysis revealed age, presence of SARS-CoV-2, and ICU admission, aOR 1.07, 11.37, and 41.95 respectively, was significantly associated with mortality risk during hospitalization; race and ethnicity were not.

CONCLUSION

Low overall incidence of thrombotic events occurred only in the SARS-CoV-2 PNA group. SARS-CoV-2 PNA may lead to higher incidence of clinical events than those observed in H3N2/H1N1 viral pneumonia, and that race/ethnicity does not drive mortality outcomes.

Antimicrobial susceptibility testing: An updated primer for clinicians in the era of antimicrobial resistance: Insights from the Society of Infectious Diseases Pharmacists

Antimicrobial susceptibility testing (AST) is a critical function of the clinical microbiology laboratory and is essential for optimizing care of patients with infectious diseases, monitoring antimicrobial resistance (AMR) trends, and informing public health initiatives. Several methods are available for performing AST including broth microdilution, agar dilution, and disk diffusion. Technological advances such as the development of commercial automated susceptibility testing platforms and the advent of rapid diagnostic tests have improved the rapidity, robustness, and clinical application of AST. Numerous accrediting and regulatory agencies are involved in the process of AST and setting and revising breakpoints, including the U.S. Food and Drug Administration and the Clinical and Laboratory Standards Institute. Challenges to optimizing AST include the emergence of new resistance mechanisms, the development of new antimicrobial agents, and generation of new data requiring updates and revisions to established methods and breakpoints. Together, the challenges in AST methods and their interpretation create important opportunities for well-informed clinicians to improve patient outcomes and provide value to antimicrobial stewardship programs, especially in the setting of rapidly changing and increasing AMR. Addressing AST challenges will involve continued development of new technologies along with collaboration between clinicians and the laboratory to facilitate optimal antimicrobial use, combat the increasing burden of AMR, and inform the development of novel antimicrobials. This updated primer serves to reinforce important principles of AST, and to provide guidance on their implementation and optimization.

1666. Sources and Preventability of Hospital-onset Bacteremia and Fungemia in the United States: Evaluation of a Potential Healthcare Quality Measure

Background

Hospital-onset bacteremia and fungemia (HOB) is being proposed as a potential healthcare quality measure due to its clinical significance, objectivity, and ease of detection. However, information is lacking on sources of HOB and the proportion and types of cases considered preventable.

Methods

We evaluated sources and potential preventability of HOB cases at 12 hospitals using retrospective chart review. HOB was defined as a positive blood culture >= day 4 (admission date=day 1) for one or more organisms. Stratified sampling of cases by commensal and noncommensal organisms was used. Infectious disease physicians determined the source of HOB and rated preventability from 1-6 (1=definitely preventable to 6=definitely not preventable) using a previously validated guide. Ratings of 1–3 were collectively considered potentially preventable and 4–6 likely not preventable.

Results

We evaluated sources and potential preventability of HOB cases at 12 hospitals using retrospective chart review. HOB was defined as a positive blood culture >= day 4 (admission date=day 1) for one or more organisms. Stratified sampling of cases by commensal and noncommensal organisms was used. Infectious disease physicians determined the source of HOB and rated preventability from 1–6 (1=definitely preventable to 6=definitely not preventable) using a previously validated guide. Ratings of 1–3 were collectively considered potentially preventable and 4–6 likely not preventable.

Conclusion

Gastrointestinal and endovascular sources account for a large majority of noncommensal HOB cases. A high proportion of noncommensal HOB cases are likely not preventable. The presence of non-preventable events should be considered when using HOB as a quality measure. Approaches to identifying the subset of preventable noncommensal HOB events should be explored.

Disclosures

Scott Fridkin, MD, Pfizer: Grant/Research Support Andi L. Shane, MD, MPH, MSc, International Scientific Association for Probiotics and Prebiotics (ISAPP): travel and lodging to attend international meeting to deliver a presentation, June 2022 Aaron Milstone, MD, Merck: Grant/Research Support Rajeshwari Nair, MBBS, PhD, Vertex Pharmaceuticals: Salary.

Activity of Delafloxacin and Levofloxacin against Stenotrophomonas maltophilia at Simulated Plasma and Intrapulmonary pH Values

Fluoroquinolones have become a popular treatment option for Stenotrophomonas maltophilia infections. Although levofloxacin is most commonly used, delafloxacin demonstrates comparable in vitro activity when evaluated under standard susceptibility testing conditions at neutral pH. At acidic pH, the activity of the anionic delafloxacin is improved, while the activity of the zwitterionic levofloxacin is reduced. Because the human respiratory tract has a pH of ~6.6 and is the most common site of S. maltophilia infection, it is vital to understand the activity of these agents in this environment. Therefore, levofloxacin and delafloxacin were tested against clinical S. maltophilia isolates via broth microdilution testing (n = 37) and time-kill analysis (n = 5) in neutral cation-adjusted Mueller-Hinton broth (CAMHB) (pH 7.3) and acidic CAMHB (aCAMHB) (pH 6.5). In CAMHB, MIC50 values were similar between levofloxacin and delafloxacin (8 mg/L versus 8 mg/L). In aCAMHB, levofloxacin MICs did not change, while delafloxacin MICs decreased by a median of 4 log2 dilutions (MIC50 values of 8 mg/L versus 0.25 mg/L). In time-kill analyses, levofloxacin and delafloxacin at the maximum drug concentration for the free drug (fCmax) were bactericidal against 3 and 2 isolates in CAMHB, respectively. In aCAMHB, levofloxacin was not bactericidal against any isolate, while delafloxacin was bactericidal against the same 2 isolates. Relative to CAMHB, levofloxacin activity was reduced by 2.5 log10 CFU/mL in aCAMHB, whereas delafloxacin activity was increased 2.7 log10 CFU/mL. Although the bactericidal activity of levofloxacin against S. maltophilia was attenuated in an acidic environment in this study, the increased potency of delafloxacin at pH 6.5 did not translate into improved bactericidal activity in time-kill analyses, compared to pH 7.3. IMPORTANCE Stenotrophomonas maltophilia most often infects the lungs, where the physiologic environment is naturally slightly acidic (pH ~6.6), compared to most parts of the body (such as the bloodstream), which have neutral pH values (~7.4). Pneumonia due to S. maltophilia is often treated with the antibiotic levofloxacin, despite the activity of levofloxacin being known to be impaired at acidic pH. Unfortunately, currently available methods for susceptibility testing of levofloxacin against S. maltophilia are performed at a neutral pH and therefore may not accurately represent the activity of levofloxacin at the site of infection in the lungs. A similar but newer antibiotic in the same class as levofloxacin, namely, delafloxacin, is not affected by being in an acidic environment and may actually work better at lower pH values. Therefore, the purpose of this study was to investigate whether one drug might be better than the other in this setting by testing each agent's ability to kill S. maltophilia at pH 7.3 and pH 6.5. These findings could then be used to design confirmatory studies that may ultimately impact which drug is given to patients with lung infections due to S. maltophilia.

The importance of pharmacokinetics and pharmacodynamics in antimicrobial drug development and their influence on the success of agents developed to combat resistant gram negative pathogens: A review

A deep understanding of an antimicrobial’s critical pharmacokinetic and pharmacodynamic properties is crucial towards optimizing its use in patients and bolstering the drug development program. With the growing threat of antimicrobial resistance and decline in antimicrobial development, the advancement of complex and rigorous pharmacokinetic and pharmacodynamic studies over a short time span has renewed confidence in the value of pharmacokinetic and pharmacodynamic studies and allowed it to become fundamental component of a robust drug development program with high chances of successful approval. In addition, recent guidance by various regulatory bodies have reinforced that a strong and dedicated focus on pharmacokinetics and pharmacodynamics throughout research and development lead to the use of an optimized dosing regimen in Phase 3 trials, improving the probability of drug approval. The objective of this review is to demonstrate the importance of pharmacokinetic and pharmacodynamic studies in the drug development decision-making process by highlighting the developments in pharmacokinetic and pharmacodynamic methods and discuss the role of pharmacokinetic and pharmacodynamic studies in antimicrobial successes and failures.

Activity of Omadacycline Alone and in Combination against Carbapenem-Nonsusceptible Acinetobacter baumannii with Varying Minocycline Susceptibility

Tetracycline-based combinations are increasingly used for serious carbapenem-nonsusceptible Acinetobacter baumannii (CNSAb) infections given their potent in vitro activity, synergism with other agents, and acceptable toxicity profile. Omadacycline is a novel aminomethylcycline with activity against minocycline-resistant pathogens, once daily oral dosing, and favorable pharmacokinetic properties. Given these potential advantages, the in vitro potency and antibacterial activity of omadacycline were evaluated alone and in combination against CNSAb with varying minocycline susceptibility. Broth microdilution testing of 41 CNSAb revealed that omadacycline (MIC50/90: 4/8 mg/L) inhibited 68.3% (28/41) of isolates at ≤4 mg/L and its activity was unaffected by minocycline nonsusceptibility (MIC50/90: 4/8 mg/L; 74.2% [23/31] inhibited at ≤4 mg/L). Ten (5 minocycline susceptible and 5 nonsusceptible) of the 41 CNSAb isolates were then evaluated in time-kill analyses against omadacycline and comparator agents alone and in dual- and triple-drug combinations at the free maximum concentration of drug in serum (fCmax). Amikacin, meropenem, and polymyxin B alone were each bactericidal against 4 of 10 (40%) isolates while omadacycline and sulbactam were bactericidal against 0 (0%) and 1 (10%), respectively. In dual-drug combinations with omadacycline, synergy was observed against 80% of isolates with sulbactam followed by 30% with amikacin or polymyxin B and 0% with meropenem or rifampin. The triple-drug combination of omadacycline, sulbactam, and polymyxin B achieved synergy against just one additional strain over the omadacycline-sulbactam dual combination but significantly reduced the time to 99.9% kill by more than 6 h (4.6 ± 2.8 h vs. 11.3 ± 5.9 h, P < 0.01). These results support the continued investigation into tetracycline-based combinations against CNSAb, particularly those including sulbactam, and suggest that omadacycline may have in vitro advantages over existing tetracycline-derivatives. IMPORTANCE Treatment of infections due to Acinetobacter baumannii often involves the use of multiple antibiotics simultaneously as combination therapy, but it is unknown which antibiotics are best used together. Tetracycline agents such as minocycline and tigecycline maintain good activity against A. baumannii and are often used with one or more other agents to achieve better killing of the bacteria. Omadacycline is a new tetracycline that may have a role in the treatment of A. baumannii, but no data are available evaluating its interaction with other commonly used drugs such as polymyxin B and sulbactam. Therefore, the purpose of this study was to investigate the antibacterial activity of omadacycline when combined with one or more other agents against carbapenem-resistant strains of A. baumannii. These findings may then be used to design confirmatory studies that could help decide what drugs work best together and what combination of agents should be used for patients.

Use of Novel Antibiograms to Determine the Need for Earlier Susceptibility Testing and Administration for New β-Lactam/β-Lactamase Inhibitors in the United States

Antimicrobial resistance is a global public health threat, and gram-negative bacteria, such as Enterobacterales and Pseudomonas aeruginosa, are particularly problematic with difficult-to-treat resistance phenotypes. To reduce morbidity and mortality, a reduction in the time to effective antimicrobial therapy (TTET) is needed, especially among critically ill patients. The antibiogram is an effective clinical tool that can provide accurate antimicrobial susceptibility information and facilitate early antimicrobial optimization, decrease TTET, and improve outcomes such as mortality, hospital length of stay, and costs. Guidance is lacking on how to validate the susceptibility to new antibacterial agents. Commonly used traditional and combination antibiograms may not adequately assist clinicians in making treatment decisions. Challenges with the current susceptibility testing of new β-lactam/β-lactamase inhibitor combinations persist, impacting the appropriate antibacterial choice and patient outcomes. Novel antibiograms such as syndromic antibiograms that incorporate resistant gram-negative phenotypes and/or minimum inhibitory concentration distributions may assist in determining the need for earlier susceptibility testing or help define an earlier optimal use of the new β-lactam/β-lactamase inhibitors. The purpose of this review is to emphasize novel antibiogram approaches that are capable of improving the time to susceptibility testing and administration for new β-lactam/β-lactamase inhibitors so that they are earlier in a patient’s treatment course.

Pharmacokinetics, Pharmacodynamics, and Dose Optimization of Cefiderocol during Continuous Renal Replacement Therapy

BACKGROUND

The need for continuous renal replacement therapy (CRRT) in critically ill patients with serious infections is associated with clinical failure, emergence of resistance, and excess mortality. These poor outcomes are attributable in large part to subtherapeutic antimicrobial exposure and failure to achieve target pharmacokinetic/pharmacodynamic (PK/PD) thresholds during CRRT. Cefiderocol is a novel siderophore cephalosporin with broad in vitro activity against resistant pathogens and is often used to treat critically ill patients, including those receiving CRRT, despite the lack of data to guide dosing in this population.

OBJECTIVE

The aim of this study was to evaluate the PK and PD of cefiderocol during in vitro and in vivo CRRT and provide optimal dosing recommendations.

METHODS

The PK and dialytic clearance of cefiderocol was evaluated via an established in vitro CRRT model across various modes, filter types, and effluent flow rates. These data were combined with in vivo PK data from nine patients receiving cefiderocol while receiving CRRT from phase III clinical trials. Optimal dosing regimens and their respective probability of target attainment (PTA) were assessed via an established population PK model with Bayesian estimation and 1000-subject Monte Carlo simulations at each effluent flow rate.

RESULTS

The overall mean sieving/saturation coefficient during in vitro CRRT was 0.90 across all modes, filter types, effluent flow rates, and points of replacement fluid dilution tested. Adsorption was negligible at 10.9%. Three-way analysis of variance (ANOVA) and multiple linear regression analyses demonstrated that effluent flow rate is the primary driver of clearance during CRRT and can be used to calculate optimal cefiderocol doses required to match the systemic exposure observed in patients with normal renal function. Bayesian estimation of these effluent flow rate-based optimal doses in nine patients receiving CRRT from the phase III clinical trials of cefiderocol revealed comparable mean (± standard deviation) area under the concentration-time curve values as patients with normal renal function (1709 ± 539 mg·h/L vs. 1494 ± 58.4 mg·h/L; p = 0.26). Monte Carlo simulations confirmed these doses achieved >90% PTA against minimum inhibitory concentrations ≤4 mg/L at effluent flow rates from 0.5 to 5 L/h.

CONCLUSION

The optimal dosing regimens developed from this work have been incorporated into the prescribing information for cefiderocol, making it the first and only antimicrobial with labeled dosing for CRRT. Future clinical studies are warranted to confirm the efficacy and safety of these regimens.

Overcoming Stenotrophomonas maltophilia Resistance for a More Rational Therapeutic Approach

Stenotrophomonas maltophilia is an underappreciated source of morbidity and mortality among Gram-negative pathogens. Effective treatment options with acceptable toxicity profiles are limited. Phenotypic susceptibility testing via commercial automated test systems is problematic and no FDA breakpoints are approved for any of the first-line treatment options for S. maltophilia. The lack of modern pharmacokinetic/ pharmacodynamic data for many agents impedes dose optimization and the lack of robust efficacy and safety data limits their clinical utility. Levofloxacin has demonstrated similar efficacy to SMX-TMP, although rapid development of resistance is a concern. Minocycline demonstrates the highest rate of in vitro susceptibility, however, evidence to support its clinical use are scant. Novel agents such as cefiderocol have exhibited promising activity in pre-clinical investigations, though additional outcomes data are needed to determine its place in therapy for S. maltophilia. Combination therapy is often employed despite the dearth of adequate supporting data.

Clinical Decision Support Systems to Reduce Unnecessary Clostridoides difficile Testing Across Multiple Hospitals

BACKGROUND

Inappropriate C. difficile testing has adverse consequences for the patient, hospital, and public health. Computerized Clinical Decision Supports (CCDS) in the Electronic Health Record (EHR) may reduce C. difficile test ordering; however, effectiveness of different approaches, ease of use, and best fit into the healthcare providers' (HCP) workflow, are not well understood.

METHODS

Nine academic and 6 community U.S. hospitals participated in this 2-year cohort study. CCDS (hard- or soft-stop) triggered when duplicate C. difficile test order attempted, or if laxatives were recently received. The primary outcome was the difference in testing rates pre- and post-CCDS interventions, using incident rate ratios (IRR) and mixed effect Poisson regression models. We performed qualitative evaluation (contextual inquiry, interviews, focus groups) based on a human factors model. We identified themes using a codebook with primary- and sub-nodes.

RESULTS

In 9 hospitals implementing hard-stop CCDS and 4 hospitals implementing soft-stop CCDS, C. difficile testing IRR reduction was 33% (95% CI, 30-36%), and 23% (95% CI 21-25%), respectively. Two hospitals implemented a non-EMR based human intervention with IRR reduction of 21% (95% CI 15-28%). HCPs reported generally favorable experiences, and highlighted time efficiencies such as inclusion of the patients most recent laxative administration on the CCDS. Organizational factors including hierarchical cultures, and communication between HCPs caring for the same patient, impact CCDS acceptance and integration.

CONCLUSIONS

CCDS reduced unnecessary C. difficile testing and were perceived positively by HCPs when integrated into their workflow, and when displayed relevant patient specific information needed for decision-making.

417. COVID-19 Aerostudy: Evaluation of SARS-CoV-2 Virus in the Air of Patients Hospitalized with COVID-19

Background

At the onset of the COVID-19 pandemic, hospitals implemented infection control measures with limited data on predictors of nosocomial SARS-CoV-2 transmission. We aimed to quantify SARS-CoV-2 presence in an inpatient setting to understand nosocomial risk.

Methods

Patients admitted with confirmed SARS-CoV-2 infection at an urban academic hospital were enrolled. Demographic/clinical characteristics, a PCR nasal swab(NS), and air samples on filter media in the near- (< 6ft) and far-field ( >6ft) of each patient for 3.5 hours were collected. PCR was used to detect SARS-CoV-2 on filter media. Associations between clinical characteristics and presence of SARS-CoV-2 in air samples used Fisher’s exact and Wilcoxon rank sum tests.

Results

Of 52 subjects, 46% had no detectable virus by nasal swab on the day of sampling. Of 104 room air samples, 16% had detectable virus from 25% of rooms, including 10 near and 7 far field samples. Subjects with a positive room air sample had fewer days from symptom-onset compared with those with a negative air sample (median 6 vs. 8, p=0.24). Being on room air and having a nasal swab positive increased the odds of detecting virus in air samples but were not statistically significant.

Conclusion

A small number of air samples with detectable SARS-CoV-2 may suggest lower nosocomial risk than previously anticipated. Multiple subject and environmental factors may have contributed to this finding including patient source control masking, anti-viral therapies and HEPA filtration. The decreased association of virus in the air of those with more days of symptoms but with the need for supplemental oxygen may be related to what is now known about the COVID-19 inflammatory response after the infectious period.

Disclosures

All Authors: No reported disclosures

Aminoglycoside-resistance gene signatures are predictive of aminoglycoside MICs for carbapenem-resistant Klebsiella pneumoniae

BACKGROUND

Aminoglycoside-containing regimens may be an effective treatment option for infections caused by carbapenem-resistant Klebsiella pneumoniae (CR-Kp), but aminoglycoside-resistance genes are common in these strains. The relationship between the aminoglycoside-resistance genes and aminoglycoside MICs remains poorly defined.

OBJECTIVES

To identify genotypic signatures capable of predicting aminoglycoside MICs for CR-Kp.

METHODS

Clinical CR-Kp isolates (n = 158) underwent WGS to detect aminoglycoside-resistance genes. MICs of amikacin, gentamicin, plazomicin and tobramycin were determined by broth microdilution (BMD). Principal component analysis was used to initially separate isolates based on genotype. Multiple linear regression was then used to generate models that predict aminoglycoside MICs based on the aminoglycoside-resistance genes. Last, the performance of the predictive models was tested against a validation cohort of 29 CR-Kp isolates.

RESULTS

Among the original 158 CR-Kp isolates, 91.77% (145/158) had at least one clinically relevant aminoglycoside-resistance gene. As a group, 99.37%, 84.81%, 82.28% and 10.76% of the CR-Kp isolates were susceptible to plazomicin, amikacin, gentamicin and tobramycin, respectively. The first two principal components explained 72.23% of the total variance in aminoglycoside MICs and separated isolates into four groups with aac(6')-Ib, aac(6')-Ib', aac(6')-Ib+aac(6')-Ib' or no clinically relevant aminoglycoside-resistance genes. Regression models predicted aminoglycoside MICs with adjusted R2 values of 56%-99%. Within the validation cohort, the categorical agreement when comparing the observed BMD MICs with the predicated MICs was 96.55%, 89.66%, 86.21% and 82.76% for plazomicin, gentamicin, amikacin and tobramycin, respectively.

CONCLUSIONS

Susceptibility to each aminoglycoside varies in CR-Kp. Detection of aminoglycoside-resistance genes may be useful to predict aminoglycoside MICs for CR-Kp.

Real-world impact of switching from tenofovir disoproxil fumarate to tenofovir alafenamide

Although tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) have been evaluated in various clinical trials, limited safety and efficacy data exist in real-world settings. The goal of this retrospective analysis is to assess changes in virological suppression, immunological status, renal function, weight and body mass index (BMI) amongst people living with HIV who switched from a TDF-based to a TAF-based regimen. Of 130 patients included in the final analysis, 53 patients experienced an increase in their viral load upon switching from TDF to TAF therapy whilst 62 patients remained undetectable. For those who experienced a viral blip, 33 (62%) resuppressed by the time of last follow-up, 15 (28%) patients did not have additional labs beyond the last follow-up and concern for failure occurred in 5 (9%) patients. No differences in immunological function, renal function, weight or BMI were observed from before switching to the last follow-up. Although a loss of virological suppression was found upon switching to TAF at subsequent follow-up visits, resuppression ultimately occurred in most patients.

Glutathione-Conjugated Hydrogels: Flexible Vehicles for Personalized Treatment of Bacterial Infections

PURPOSE

Skin and soft tissue infections are increasingly prevalent and often complicated by potentially fatal therapeutic hurdles, such as poor drug perfusion and antibiotic resistance. Delivery vehicles capable of versatile loading may improve local bioavailability and minimize systemic toxicities yet such vehicles are not clinically available. Therefore, we aimed to expand upon the use of glutathione-conjugated poly(ethylene glycol) GSH-PEG hydrogels beyond protein delivery and evaluate the ability to deliver traditional therapeutic molecules.

METHODS

PEG and GSH-PEG hydrogels were prepared using ultraviolet light (UV)-polymerization. Hydrogel loading and release of selected drug candidates was examined using UV-visible spectrometry. Therapeutic molecules and GST-fusion protein loading was examined using UV-visible and fluorescent spectrometry. Efficacy of released meropenem was assessed against meropenem-sensitive and -resistant P. aeruginosa in an agar diffusion bioassay.

RESULTS

For all tested agents, GSH-PEG hydrogels demonstrated time-dependent loading whereas PEG hydrogels did not. GSH-PEG hydrogels released meropenem over 24 h. Co-loading of biologic and traditional therapeutics into a single vehicle was successfully demonstrated. Meropenem-loaded GSH-PEG hydrogels inhibited the growth of meropenem-sensitive and resistant P. aeruginosa isolates.

CONCLUSION

GSH ligands within GSH-PEG hydrogels allow loading and effective delivery of charged therapeutic agents, in addition to biologic therapeutics.

The Impact of Body Weight and Renal Function on the Risk of Bleeding With Direct Oral Anticoagulants in Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) increases the risk of stroke and direct oral anticoagulants (DOACs) are first-line agents for prevention. Gaps in the literature cause reluctance in prescribing DOACs for patients with renal dysfunction and/or extremes in body weight.

OBJECTIVE

To evaluate the impact body weight and renal function have on major and clinically relevant nonmajor (CRNM) bleeding events and ischemic strokes in AF patients receiving a DOAC.

METHODS

This retrospective cohort study included adults with nonvalvular atrial fibrillation (NVAF) or atrial flutter (AFL) receiving a DOAC ≥12 months. The primary outcome was a composite of major and CRNM bleeding events. Secondary outcomes included ischemic stroke and risk factors for bleeding events.

RESULTS

Of the 233 patients analyzed, 25 patients experienced a bleeding event. Patients who bled weighed 10 kg less (P = 0.043) than those who did not and had a higher HASBLED score (P = 0.003). Multivariate logistic regression identified weight (P = 0.048), serum creatinine (SCr; P = 0.027), and HASBLED score (P = 0.024) as the significant predictors for experiencing a bleed. Three patients experienced a stroke.

CONCLUSION AND RELEVANCE

This study demonstrates an association between higher baseline SCr, elevated HASBLED score, and lower weight, with an increased risk of bleeding in patients with NVAF or AFL receiving a DOAC. These findings add to prescribing considerations when initiating DOACs. Closer monitoring is advised for patients with significant renal dysfunction and/or low body weight, even with renal dose adjustments.

Pharmacokinetics and dialytic clearance of apixaban during in vitro continuous renal replacement therapy

Background

To evaluate the transmembrane clearance (CL_TM) of apixaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations.

Methods

Apixaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of apixaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for apixaban were estimated via noncompartmental analysis. CL_TM was calculated via the estimated area under the curve (AUC) and by the product of the sieving/saturation coefficient (SC/SA) and flow rate. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CL_TM by each method. Optimal doses were suggested by matching the AUC observed in vitro to the systemic exposure demonstrated in Phase 2/3 studies of apixaban. Linear regression was utilized to provide dosing estimations for flow rates from 0.5–5 L/h.

Results

Mean adsorption to the HF1400 and M150 filters differed significantly at 38 and 13%, respectively, while mean (± standard deviation, SD) percent protein binding was 70.81 ± 0.01%. Effect of CVVH point of dilution did not differ across filter types, although CL_TM was consistently significantly higher during CRRT with the HF1400 filter compared to the M150. The three-way ANOVA demonstrated improved fit when CL_TM values calculated by AUC were used (adjusted R² 0.87 vs. 0.52), and therefore, these values were used to generate optimal dosing recommendations. Linear regression revealed significant effects of filter type and flow rate on CL_TM by AUC, suggesting doses of 2.5–7.5 mg twice daily (BID) may be needed for flow rates ranging from 0.5–5 L/h, respectively.

Conclusion

For CRRT flow rates most commonly employed in clinical practice, the standard labeled 5 mg BID dose of apixaban is predicted to achieve target systemic exposure thresholds. The safety and efficacy of these proposed dosing regimens warrants further investigation in clinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02248-7.

Therapeutic Options for Metallo-β-Lactamase-Producing Enterobacterales

The spread of metallo-β-lactamase (MBL)-producing Enterobacterales worldwide without the simultaneous increase in active antibiotics makes these organisms an urgent public health threat. This review summarizes recent advancements in diagnostic and treatment strategies for infections caused by MBL-producing Enterobacterales. Adequate treatment of patients infected with MBL-producing Enterobacterales relies on detection of the β-lactamase in the clinic. There are several molecular platforms that are currently available to identify clinically relevant MBLs as well as other important serine-β-lactamases. Once detected, there are several antibiotics that have historically been used for the treatment of MBL-producing Enterobacterales. Antimicrobials such as aminoglycosides, tetracyclines, fosfomycin, and polymyxins often show promising in vitro activity though clinical data are currently lacking to support their widespread use. Ceftazidime-avibactam combined with aztreonam is promising for treatment of infections caused by MBL-producing Enterobacterales and currently has the most clinical data of any available antibiotic to support its use. While cefiderocol has displayed promising activity against MBL-producing Enterobacterales in vitro and in preliminary clinical studies, further clinical studies will better shed light on its place in treatment. Lastly, there are several promising MBL inhibitors in the pipeline, which may further improve the treatment of MBL-producing Enterobacterales.

Safety and Efficacy of Apixaban For Therapeutic Anticoagulation in Critically Ill ICU Patients with Severe COVID-19 Respiratory Disease

Introduction  Despite the use of unfractionated heparin (UFH) or low molecular weight heparin (LMWH), rates of thromboembolic disease, and subsequent morbidity and mortality remain unacceptably high in patients with severe novel coronavirus disease 2019 (COVID-19) disease. Direct oral anticoagulants (DOACs), such as apixaban, have numerous purported benefits although the safety and efficacy of their use in intensive care unit (ICU) patients with severe COVID-19 has yet to be evaluated.

Materials and Methods  Single-center, retrospective cohort study of 21 ICU patients with severe COVID-19 respiratory disease treated with apixaban for atrial fibrillation (AFib), venous thromboembolism (VTE), catheter-induced thrombosis, and/or COVID-19-induced coagulopathy. The primary objective was to evaluate the incidence of bleeding events and secondary objectives included thromboembolic events, coagulation parameters, and mortality.

Results  Ninety percent of patients were non-White, 43% were obese, 90% had acute respiratory distress syndrome, and 76% required mechanical ventilation. Nearly half of (47.6%) also experienced renal dysfunction and required renal replacement therapy. Eighty-six percent of patients received prophylaxis or treatment with UFH or LMWH within the 24-hour period prior to apixaban initiation. Patients were initiated on apixaban for the treatment of suspected or confirmed VTE (67%) or AFib (33%). All coagulation parameters remained abnormal but stable throughout the 10-day monitoring period. No patients experienced any major bleeding events or thrombosis throughout the study period. There were four deaths during the follow-up period, all deemed unrelated to coagulopathy or bleeding.

Conclusion  Apixaban appeared safe and efficacious in ICU patients with severe COVID-19 disease. These data encourage future trials seeking to optimize anticoagulation strategies in patients with severe COVID-19.

Development of a method for clinical pharmacokinetic testing to allow for targeted Melphalan dosing in multiple myeloma patients undergoing autologous transplant

AIMS

High dose melphalan (HDM) and autologous stem cell transplant (ASCT) is standard of care for multiple myeloma (MM), but there is significant variability in melphalan exposure (area under the plasma drug concentration-time curve, AUC) when using body surface area-based dosing. Our aim was to establish a method of pharmacokinetic (PK) testing for real-time melphalan dose adjustments.

METHODS

We performed a prospective PK study of melphalan 140 or 200 mg/m2 in MM patients undergoing ASCT. Twenty MM patients were administered HDM on days -2 and - 1, with PK sampling at 8-10 time points. PK testing was performed on day -2 in all patients, and on day -1 in 5 patients.

RESULTS

Less than 20% interpatient variation in the day -2 and - 1 AUC was observed. The day -2 range in AUC (4.95-11.28 mg h/L) confirmed significant interpatient variability. The hypothetical total dose ranged from 133-302 mg/m2 to achieve the total median AUC. A 4-time point AUC (0, 30, 150 and 240 min) highly correlated with the AUC from the 8-time point schedule. A higher AUC correlated with increased risk of febrile neutropenia (P = .05).

CONCLUSION

Here we outline the methods to establish novel melphalan dosing using PK testing in MM patients undergoing ASCT to target a desired melphalan AUC.

An Appraisal of the Pharmacokinetic and Pharmacodynamic Properties of Meropenem-Vaborbactam

Carbapenem-resistant gram-negative pathogens remain an urgent public health threat, and safe, effective treatment options are limited. Although several agents are now available to combat these infections, meropenem-vaborbactam was the first to combine a novel, cyclic, boronic acid-based, β-lactamase inhibitor with a carbapenem backbone. Vaborbactam emanated from a discovery program specifically designed to identify candidate β-lactamase inhibitors with biochemical, microbiologic, and pharmacologic properties optimized for use in conjunction with a carbapenem. Meropenem was selected as the ideal carbapenem given its broad-spectrum in vitro activity, well established safety profile, and proven efficacy in the treatment of serious gram-negative infections. The combination has demonstrated potent in vitro activity against resistant gram-negative pathogens, particularly KPC-producing Klebsiella pneumoniae (MIC₅₀ values typically ≤ 0.06 mg/l). Importantly, the pharmacokinetic (PK) profiles of the two agents are well matched, and the approved optimized dosing regimen of 4 g every 8 h (Q8h) as a 3-h infusion provides reliable probability of target attainment against the majority of commonly encountered carbapenem-resistant Enterobacteriaceae (CRE). Robust in vitro and in vivo PK/pharmacodynamic (PD) data support the ability of this dosing regimen to achieve specified PK/PD targets for both bactericidal activity and prevention of resistance among pathogens with MICs up to 8 mg/l. This concerted effort into optimizing the PK and PD parameters of both the β-lactam and β-lactamase inhibitor alone and in combination contributed to the clinical success of meropenem-vaborbactam demonstrated in phase 3 trials in patients with complicated urinary tract infections (cUTI), including acute pyelonephritis (AP), and serious CRE infections. As the use of meropenem-vaborbactam increases concomitantly with the prevalence of KPC-producing CRE, continued pharmacovigilance and antimicrobial stewardship efforts will be of upmost importance to ensure that these PK/PD efforts translate into improved patient outcomes.

Activity of aztreonam in combination with ceftazidime-avibactam against serine- and metallo-β-lactamase-producing Pseudomonas aeruginosa

Existing data support the combination of aztreonam and ceftazidime-avibactam against serine-β-lactamase (SBL)- and metallo-β-lactamase (MBL)-producing Enterobacterales, although there is a paucity of data against SBL- and MBL-producing Pseudomonas aeruginosa. In this study, 5 SBL- and MBL-producing P. aeruginosa (1 IMP, 4 VIM) were evaluated against aztreonam and ceftazidime-avibactam alone and in combination via broth microdilution and time-kill analyses. All 5 isolates were nonsusceptible to aztreonam, aztreonam-avibactam, and ceftazidime-avibactam. Combining aztreonam with ceftazidime-avibactam at subinhibitory concentrations produced synergy and restored bactericidal activity in 4/5 (80%) isolates tested. These results suggest that the combination of aztreonam and ceftazidime-avibactam may be a viable treatment option against SBL- and MBL-producing P. aeruginosa.

Activity of Cefiderocol Alone and in Combination with Levofloxacin, Minocycline, Polymyxin B, or Trimethoprim-Sulfamethoxazole against Multidrug-Resistant Stenotrophomonas maltophilia

The production of an L1 metallo-β-lactamase and an L2 serine active-site β-lactamase precludes the use of β-lactams for the treatment of Stenotrophomonas maltophilia infections. Preclinical data suggest that cefiderocol is the first approved β-lactam with reliable activity against S. maltophilia, but data on strains resistant to current first-line agents are limited, and no studies have assessed cefiderocol-based combinations. The objective of this study was to evaluate and compare the in vitro activity of cefiderocol alone and in combination with levofloxacin, minocycline, polymyxin B, or trimethoprim-sulfamethoxazole (TMP-SMZ) against a collection of highly resistant clinical S. maltophilia isolates. For this purpose, the MICs of cefiderocol, ceftazidime, levofloxacin, minocycline, polymyxin B, and TMP-SMZ for 37 S. maltophilia isolates not susceptible to levofloxacin and/or TMP-SMZ were determined. Nine strains with various cefiderocol MICs were then tested in time-kill experiments with cefiderocol alone and in combination with comparators. The only agents for which susceptibility rates exceeded 40% were cefiderocol (100%) and minocycline (97.3%). Cefiderocol displayed the lowest MIC50 and MIC90 values (0.125 and 0.5 mg/liter, respectively). In time-kill experiments, synergy was observed when cefiderocol was combined with levofloxacin, minocycline, polymyxin B, or TMP-SMZ against 4/9 (44.4%), 6/9 (66.7%), 5/9 (55.5%), and 6/9 (66.7%) isolates, respectively. These data suggest that cefiderocol displays potent in vitro activity against S. maltophilia, including strains resistant to currently preferred agents. Future dynamic and in vivo studies of cefiderocol alone and in combination are warranted to further define cefiderocol's synergistic capabilities and its place in therapy for S. maltophilia infections.

In vitro activity of oritavancin alone or in combination against vancomycin-susceptible and -resistant enterococci

OBJECTIVES

The optimal treatment for serious infections due to Enterococcus spp. is unknown although combination antimicrobial therapy is often recommended for invasive infections to achieve bactericidal activity and improve clinical outcomes. Oritavancin is a novel lipoglycopeptide agent with in vitro activity against enterococci, including vancomycin-resistant VanA-type Enterococcus faecium. Data on its activity in combination with other antibacterials are limited. The objective of this study was to evaluate the activity of oritavancin alone and in combination with ceftriaxone, daptomycin, gentamicin, linezolid and rifampicin against vancomycin-susceptible and -resistant enterococci in in vitro time-kill analyses.

METHODS

Five enterococcal strains were used for all experiments: three vancomycin-resistant VanA-type E. faecium clinical bloodstream isolates, vancomycin-resistant VanA-type E. faecium ATCC 700221 and vancomycin-susceptible Enterococcus faecalis ATCC 29212. Individual drugs were tested at ¼, ½, 1, 2 and 4× MIC. Oritavancin combination experiments were performed with each agent at ¼× MIC.

RESULTS

Daptomycin was the most active single agent and was bactericidal against all strains at 4× MIC, followed by oritavancin, which was bactericidal against all three clinical VRE strains at ≥2× MIC. In combination experiments at ¼× MIC, oritavancin was synergistic with gentamicin against strains not displaying high-level aminoglycoside resistance. No other synergy against VRE strains was observed in any experiment. Strain- and drug-dependent antagonism was observed for many combinations.

CONCLUSIONS

These in vitro data do not support the routine use of combination therapy with oritavancin in the treatment of infections due to VRE.

Performance of ceftazidime/avibactam susceptibility testing methods against clinically relevant Gram-negative organisms

OBJECTIVES

To ensure the accuracy of susceptibility testing methods for ceftazidime/avibactam.

METHODS

The performances of the Etest (bioMérieux), 30/20 μg disc (Hardy diagnostics) and 10/4 μg disc (Mast Group) were evaluated against the reference broth microdilution (BMD) method for 102 clinically relevant Gram-negative organisms: 69 ceftazidime- and meropenem-resistant Klebsiella pneumoniae and 33 MDR non-K. pneumoniae. Essential and categorical agreement along with major and very major error rates were determined according to CLSI guidelines.

RESULTS

A total of 78% of isolates were susceptible to ceftazidime/avibactam. None of the three methods met the defined equivalency threshold against all 102 organisms. The Etest performed the best, with categorical agreement of 95% and major errors of 6.3%. Against the 69 ceftazidime- and meropenem-resistant K. pneumoniae, only the Etest and the 10/4 μg disc met the equivalency threshold. None of the three methods met equivalency for the 33 MDR isolates. There were no very major errors observed in any analysis. These results were pooled with those from a previous study of 74 carbapenem-resistant Enterobacteriaceae and data from the ceftazidime/avibactam new drug application to define optimal 30/20 μg disc thresholds using the error-rate bound model-based approaches of the diffusion breakpoint estimation testing software. This analysis identified a susceptibility threshold of ≤19 mm as optimal.

CONCLUSIONS

Our data indicate that the Etest is a suitable alternative to BMD for testing ceftazidime/avibactam against ceftazidime- and meropenem-resistant K. pneumoniae. The 30/20 μg discs overestimate resistance and may lead to the use of treatment regimens that are more toxic and less effective.

A coup d'état by NDM-producing Klebsiella pneumoniae overthrows the major bacterial population during KPC-directed therapy

The objective of this study was to utilize a co-culture hollow-fiber infection model (HFIM) to characterize the interplay between a small, difficult-to-detect, New Delhi metallo-β-lactamase-producing Klebsiella pneumoniae (NDM-Kp) minor population and a larger K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae population in the presence of KPC-directed antibacterial therapy. Selective plating onto agar with ceftazidime-avibactam was used to track the density of the NDM-Kp population. Susceptibility testing and the Verigene System failed to identify the small initial NDM-Kp population. However, a ceftazidime-avibactam Etest detected resistant colonies that were confirmed to be NDM-Kp. In the HFIM, all of the investigated drug regimens caused regrowth within 24 h and resulted in >10⁹ CFU/mL of NDM-Kp. Our study demonstrates that the HFIM is a powerful tool for studying the population dynamics of multiple pathogens during antimicrobial exposure and also highlights that difficult-to-detect minor populations of drug-resistant bacteria may cause treatment failure without appropriate antibacterial therapy.

In Vitro Pharmacodynamic Analyses Help Guide the Treatment of Multidrug-Resistant Enterococcus faecium and Carbapenem-Resistant Enterobacter cloacae Bacteremia in a Liver Transplant Patient

Background

Infections due to multidrug-resistant pathogens are particularly deadly and difficult to treat in immunocompromised patients, where few data exist to guide optimal antimicrobial therapy. In the absence of adequate clinical data, in vitro pharmacokinetic (PK)/pharmacodynamic (PD) analyses can help to design treatment regimens that are bactericidal and may be clinically effective.

Methods

We report a case in which in vitro pharmacodynamic analyses were utilized to guide the treatment of complex, recurrent bacteremias due to vancomycin-, daptomycin-, and linezolid-resistant Enterococcus faecium and carbapenem-resistant Enterobacter cloacae complex in a liver transplant patient.

Results

Whole-genome sequencing revealed unique underlying resistance mechanisms and explained the rapid evolution of phenotypic resistance and complicated intrahost genomic dynamics observed in vivo. Performing this comprehensive genotypic and phenotypic testing and time-kill analyses, along with knowledge of institution and patient-specific factors, allowed us to use precision medicine to design a treatment regimen that maximized PK/PD.

Conclusions

This work provides a motivating example of clinicians and scientists uniting to optimize care in the era of escalating antimicrobial resistance.

Activity of ceftazidime-avibactam alone and in combination with polymyxin B against carbapenem-resistant Klebsiella pneumoniae in a tandem in vitro time-kill/in vivo Galleria mellonella survival model analysis

Ceftazidime-avibactam is used clinically in combination with a polymyxin for the treatment of carbapenem-resistant Gram-negative infections; however, there are limited data to support this practice. The objective of this study was to evaluate the activity of ceftazidime-avibactam and polymyxin B alone and in combination against Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae in a tandem in vitro time-kill/in vivo Galleria mellonella survival model assay. Three KPC-3-producing K. pneumoniae clinical isolates were used for all experiments. All isolates harbored mutations in ompk35 and one isolate in ompk36; two isolates were susceptible to both ceftazidime-avibactam and polymyxin B, and one was resistant to both. Ceftazidime-avibactam was bactericidal against 2 of 3 strains at ≥2x minimum inhibitory concentration (MIC) whereas polymyxin B was not bactericidal against any strain at any concentration. Combinations at 1/4x or 1/2x MIC were not bactericidal or synergistic against any of the 3 isolates. In survival experiments, ceftazidime-avibactam at 4x MIC significantly improved larval survival over the untreated control strain whereas polymyxin B at 4x MIC did not. Combining polymyxin B with ceftazidime-avibactam at 4x MIC did not improve survival compared to ceftazidime-avibactam alone. This work indicates there is no improvement in in vitro bactericidal activity or in vivo efficacy when polymyxin B is combined with ceftazidime-avibactam against KPC-producing K. pneumoniae. This combination should be avoided in lieu of ceftazidime-avibactam alone or other potentially more efficacious, less toxic combination regimens.

Multidrug Resistant Acinetobacter baumannii: Resistance by Any Other Name Would Still be Hard to Treat

PURPOSE OF REVIEW

Acinetobacter baumannii (AB) is an infamous nosocomial pathogen with a seemingly limitless capacity for antimicrobial resistance, leading to few treatment options and poor clinical outcomes. The debatably low pathogenicity and virulence of AB are juxtaposed by its exceptionally high rate of infection-related mortality, likely due to delays in time to effective antimicrobial therapy secondary to its predilection for resistance to first-line agents. Recent studies of AB and its infections have led to a burgeoning understanding of this critical microbial threat and provided clinicians with new ammunition for which to target this elusive pathogen. This review will provide an update on the virulence, resistance, diagnosis, and treatment of multidrug resistant (MDR) AB.

RECENT FINDINGS

Advances in bacterial genomics have led to a deeper understanding of the unique mechanisms of resistance often present in MDR AB and how they may be exploited by new antimicrobials or optimized combinations of existing agents. Further, improvements in rapid diagnostic tests (RDTs) and their more pervasive use in combination with antimicrobial stewardship interventions have allowed for more rapid diagnosis of AB and decreases in time to effective therapy. Unfortunately, there remains a paucity of high-quality clinical data for which to inform the optimal treatment of MDR AB infections. In fact, recently completed studies have failed to identify a combination regimen that is consistently superior to monotherapy, despite the benefits demonstrated in vitro. Encouragingly, new and updated guidelines offer strategies for the treatment of MDR AB and may help to harmonize the use of high toxicity agents such as the polymyxins. Finally, new antimicrobial agents such as eravacycline and cefiderocol have promising in vitro activity against MDR AB but their place in therapy for these infections remains to be determined. Notwithstanding available clinical trial data, polymyxin-based combination therapies with either a carbapenem, minocycline, or eravacycline remain the treatment of choice for MDR, particularly carbapenem-resistant, AB. Incorporating antimicrobial stewardship intervention with RDTs relevant to MDR AB can help avoid potentially toxic combination therapies and catalyze the most important modifiable risk factor for mortality-time to effective therapy. Further research efforts into pharmacokinetic/pharmacodynamic-based dose optimization and clinical outcomes data for MDR AB continue to be desperately needed.

Association Between Estimated Pharmacokinetic/Pharmacodynamic Predictions of Efficacy and Observed Clinical Outcomes in Obese and Nonobese Patients With Enterobacteriaceae Bloodstream Infections

Background

Evidence on pharmacokinetic/pharmacodynamic (PK/PD) alterations and clinical outcomes in obese patients with serious infections remains limited. This study aimed to evaluate predicted PK/PD indices of efficacy and observed clinical outcomes between obese and nonobese patients receiving cefepime or piperacillin-tazobactam for Enterobacteriaceae bacteremia.

Methods

This was a retrospective study of adult inpatients from 1/2012 to 9/2015 with Enterobacteriaceae bacteremia who received empiric cefepime or piperacillin-tazobactam. The primary outcome was clinical cure. First-dose free-drug exposure was estimated via predicted concentrations generated from population PK analyses and used to assess PD target attainment (>50% fT > minimum inhibitory concentration [MIC]) for the specific Enterobacteriaceae isolate. Multivariable logistic regression was utilized to identify independent predictors of clinical cure.

Results

One hundred forty-two patients were included, 57 obese and 85 nonobese. Clinical cure was achieved in 68.4% of obese and 62.4% of nonobese patients (P = .458). No significant difference in outcomes was observed when evaluated by World Health Organization (WHO) obesity classes. The PK/PD target was achieved in 98.2% of obese and 91.8% of nonobese patients (P = .144). Independent predictors of clinical cure were immunosuppression and a shorter duration of bacteremia. Obesity was not identified as a significant predictor of clinical outcomes.

Conclusions

Neither predicted PK/PD parameters nor clinical outcomes differed significantly between obese and nonobese patients treated with piperacillin-tazobactam or cefepime. As the majority of patients received extended-infusion piperacillin-tazobactam for bacteremia due to pathogens with low MICs, the potentially detrimental pathophysiologic derangements caused by obesity may not have been realized. Further studies are warranted to establish the optimal treatment of serious infections in obese patients.

2269. Clinical Outcomes in Patients with Carbapenem-Non-Susceptible, β-Lactam-Susceptible Pseudomonas aeruginosa Infections

Background

Pseudomonas aeruginosa (PsAr) isolates harboring OprD mutations often present phenotypically as carbapenem nonsusceptible but susceptible to antipseudomonal β-lactams (APBLs). It is unknown whether this unique genotype–phenotype combination affects the clinical outcomes of patients infected with these pathogens. The objective of this study was to compare clinical outcomes of patients treated with APBLs for pneumonia and/or bacteremia caused by PsAr bearing this unique carbapenem nonsusceptible, β-lactam susceptible phenotype (Carba-NS) to those retaining susceptibility to both carbapenems and APBLs (Carba-S).

Methods

Retrospective multicenter cohort of adult in-patients who received effective APBL for PsAr pneumonia and/or bacteremia from January 2012 to November 2018. Baseline characteristics, treatment information, and clinical outcomes were obtained from the electronic medical record. The primary outcome was 14-day mortality. Secondary outcomes included 30-day mortality, 30-day infection recurrence, and infection-related length of stay (IR-LOS). IR-LOS was defined as the time from index culture to antibiotic discontinuation or hospital discharge, whichever was sooner. Descriptive statistics were analyzed using SPSS.

Results

387 patients were evaluated; 60 Carba-S and 21 Carba-NS were included. The primary reason for exclusion was ineffective empiric therapy. Select demographics and clinical outcomes are displayed in Table 1. Compared with the Carba-S group, Carba-NS patients were younger, had better renal function, increased incidence of pneumonia, more severely ill, and higher rate of empiric ceftazidime use. Despite these differences at baseline there were no significant differences in empiric APBL treatment patterns, 14- or 30-day mortality, or recurrence at 30 days between the groups. Carba-NS patients had lower rate of oral step down therapy and a significantly longer LOS and IR-LOS.

Conclusion

In this cohort of patients who received appropriate and timely APBL therapy, the Carba-NS phenotype was not associated with increased rates of 14-day mortality, 30-day mortality, or 30-day infection recurrence. These data suggest that APBLs may be effective therapeutic options against this phenotype. Further research is warranted to confirm these findings.

Disclosures

All authors: No reported disclosures.

2004. Impact of Procalcitonin Roll-out Without Antimicrobial Stewardship Guidance in a Community Hospital Emergency Department

Background

Lower respiratory tract infections (LRTIs) are one of the most common infectious disease-related emergency department (ED) visits in the United States. The ID Society of America and the Agency for Healthcare Research and Quality support the use of procalcitonin (PCT) for antimicrobial stewardship (ASP) in LRTI. Though not widely available, awareness and access to PCT is rising. At our facility, PCT became available in February 2018. The aim of our study is to assess the impact of PCT at an urban community hospital and identify possible targets for ASP interventions.

Methods

Retrospective review of cases from February to August 2018. Cases from the ED were selected for review. Appropriateness of testing was assessed, defined as guideline-based use for cessation of antibiotics in uncomplicated LRTIs without critical illness or immunosuppression. Demographic variables and clinical characteristics, such as, diagnosis, antimicrobial use and PCT levels were obtained.

Results

PCT was ordered 268 times hospital-wide, of which 160 (60%) were in the ED. Ages ranged from 0–90, with an average of 47. Most cases were male (51%). Appropriate testing for LRTI occurred in 33 (29%) cases. Antimicrobials were used in 75% of cases with low (< 0.5) PCT levels (Figure 1). Length of stay (LOS) was higher in groups that received antimicrobials (Figure 2). Testing was not appropriate in 127 cases (71%), with upper respiratory (21%), soft-tissue (17%), genitourinary (15%) and abdominal (13%) infections as the most common reasons for testing. Other diagnosis included alcohol withdrawal, seizures and altered mental status. Cumulative cost of PCT testing was $24000, of which $19050 was not consistent with guidelines.

Conclusion

Clinicians routinely ordered PCT in the ED. Antimicrobials were used for LRTIs despite low PCT levels. This may have contributed to higher LOS and excess antimicrobial use. Unwarranted PCT testing had a cost of $19050. As PCT becomes widely available in hospitals across the United States, education and decision support by ASP to clinicians may be needed to enhance guideline-appropriate evidence-based use of PCT. Targeted ASP interventions in the ED may have cost savings by reducing excess testing, length of stay and improving antimicrobial use.

Disclosures

All authors: No reported disclosures.

Pharmacokinetic/pharmacodynamic predictions and clinical outcomes of patients with augmented renal clearance and Pseudomonas aeruginosa bacteremia and/or pneumonia treated with extended infusion cefepime versus extended infusion piperacillin/tazobactam

Aim

We sought to correlate pharmacokinetic (PK)/pharmacodynamic (PD) predictions of antibacterial efficacy and clinical outcomes in patients with augmented renal clearance (ARC) and Pseudomonas aeruginosa bacteremia or pneumonia treated with extended infusion cefepime or piperacillin/tazobactam.

Materials and Methods

Cefepime (2 g every 8 h) and piperacillin/tazobactam (4.5 g every 8 h) were administered over 4 h after a loading dose infused over 30 min, and minimum inhibitory concentration was determined by E-test. Published population PK evaluations in critically ill patients were used, and PD analyses were conducted using estimated patient-specific PK parameters and known minimum inhibitory concentration values for P. aeruginosa. Concentration-time profiles were generated every 6 min using first-dose drug exposure estimates including a loading infusion, and free concentration above the minimum inhibitory concentration (fT> MIC) was estimated. Clinical cure was defined as resolution of signs and symptoms attributable to P. aeruginosa infection without need for escalation of antimicrobial.

Results

One hundred and two patients were included (36 cefepime and 66 piperacillin/tazobactam). The two groups of patients had similar age, serum creatinine, weight, and creatinine clearance. The majority of patients required intensive care unit care (63.9% vs. 63.6%) and most had pneumonia (61%). The fT>MIC (93.6 [69.9-100] vs. 57.2 [47.6-72.4], P < 0.001) and clinical cure (91.7% vs. 74.2%, P = 0.039) were significantly higher in cefepime group, whereas mortality (8.3% vs. 22.7%, P = 0.1) and infection-related mortality (0% vs. 2%, P = 0.54) were similar.

Conclusions

Patients with ARC and P. aeruginosa pneumonia and/or bacteremia who received extended-infusion cefepime achieved higher fT>MIC and clinical cure than those receiving extended infusion piperacillin/tazobactam.

A randomized, open-label pharmacokinetic trial of tacrolimus extended-release dosing in obese de novo kidney transplant recipients

PURPOSE

Tacrolimus extended-release (TAC-ER; Astagraf XL^® ) is utilized in many immunosuppressive regimens post-renal transplantation. Current dosing recommendation for the TAC-ER in renal transplant is 0.15-0.2 mg/kg/day administered once daily. The purpose of this study was to determine the best method of dosing TAC-ER in obese renal transplant recipients.

METHODS

De novo obese kidney transplant recipients were randomized to receive TAC-ER 0.15 mg/kg/day based on either adjusted body weight (aBW) or ideal body weight (IBW). Post-transplant patients underwent three pharmacokinetic assessments over 14 days. The primary endpoint was the difference in TAC-ER exposure (AUC0-24) in obese patients dosed using aBW compared with IBW.

RESULTS

A total of 20 obese renal transplant recipients were randomized to participate in the study (10 aBW and 10 IBW). Results of the primary outcome (AUC0-24) on Study Day 1, 7, and 14 were not statistically different between the two groups. There was no difference in the number of days to therapeutic trough concentration between the two dosing weights (aBW = 5.1, IBW = 4.9, days; P = 0.90).

CONCLUSION

In a population of obese renal transplant recipients, comparable trough concentrations and overall exposure in both groups indicate that IBW may be preferred, as less initial drug was needed to attain adequate exposure.

2451. Synergistic Activity of Ceftazidime–Avibactam in Combination With Polymyxin B Against Carbapenem-Resistant Klebsiella pneumoniae

Background

Methods

Results

Conclusion

Disclosures

2443. Searching for the Optimal Treatment Regimen for Metallo-β-Lactamase Producing Enterobacteriaceae: Aztreonam Plus Ceftazidime–Avibactam vs. Aztreonam Plus Meropenem–Vaborbactam

Background

Pathogens harboring metallo-β-lactamase (MBL) enzymes pose a large threat to public health. Aztreonam (ATM) is not hydrolyzed by MBLs but is inactivated by other β-lactamases, which are often co-harbored in MBL-producers. Ceftazidime/avibactam (CAZ/AVI) and meropenem/vaborbactam (MER/VBR) are novel β-lactam/β-lactamase inhibitors (BL/BLI) with potent activity against serine β-lactamase producing Enterobacteriaceae. Combining ATM with BL/BLI agents may provide activity against Enterobacteriaceae producing serine and MBLs.

Methods

Two clinical E. coli isolates were used. MICs were determined in triplicate and modal values are reported. Time kill analyses were performed in triplicate at standard inoculum (10⁶). Each agent was tested alone and in combination at either fCmax or ¼, ½, 1, 2, or 4× MIC based on susceptibility. Bactericidal activity was ≥3 log₁₀ reduction in CFU/mL from the starting inoculum. Synergy was ≥2 log₁₀ reduction in CFU/mL compared with the most active agent alone. Antagonism was ≥2 log₁₀ increase in CFU/mL compared with the most active agent alone.

Results

Genotypic/phenotypic susceptibilities are in Table 1. Against EC-1, ATM alone at fCmax had no activity. When combined with CAZ/AVI or MER/VBR, respectively, synergy was observed with average log₁₀ decrease in CFU/mL at 24 hours of 3.92 and 5.04 (Figure 1a). Synergy seemed to be driven solely by the addition of the BLI as ATM/CAZ and ATM/MER did not demonstrate synergy (Figure 1a). Against EC-2, ATM alone at 1/4× MIC showed no activity (Figure 1b). Combining ATM with either CAZ/AVI or MER/VBR did not improve the activity or demonstrate synergy (Figure 1b). Interestingly, removing CAZ significantly improved the activity of ATM/AVI.

Conclusion

There were no significant differences in activity or synergy observed between the combinations of ATM with either CAZ/AVI or MER/VBR against serine- and MBL-producing E. coli. Synergy appears to be driven by the ATM-BLI combinations, with ATM-AVI demonstrating more consistent synergy than ATM-VBR. Further studies including more isolates and combinations are warranted.

Disclosures

E. Wenzler, Melinta Therapeutics: Speaker’s Bureau, Speaker honorarium.

Implementation and optimization of molecular rapid diagnostic tests for bloodstream infections

PURPOSE

The implementation and optimization of molecular rapid diagnostic tests (mRDTs) as an antimicrobial stewardship intervention for patients with bloodstream infections (BSIs) are reviewed.

SUMMARY

All U.S. acute care hospitals accredited by the Joint Commission are required to implement an antimicrobial stewardship program (ASP). Of the many interventions available to ASPs, mRDTs have demonstrated consistent, meaningful results on antimicrobial optimization and patient outcomes. Even among infectious diseases and antimicrobial stewardship-trained pharmacists, significant knowledge and familiarity gaps exist regarding available mRDTs and how best to implement and optimize them. Given the paucity of infectious diseases and/or antimicrobial stewardship-trained pharmacists, the mandates for establishing ASPs will require non-infectious diseases/antimicrobial stewardship-trained pharmacists to implement stewardship interventions, which may include mRDTs, within their institution. Optimization of mRDTs requires adequate diagnostic stewardship, specifically evaluating how mRDT implementation may decrease costs and assist in meeting antimicrobial stewardship regulatory requirements. Knowledge of how these technologies will augment existing microbiology and antimicrobial stewardship workflow is essential. Finally, selecting the right mRDT necessitates familiarity with the instrument's capabilities and with the institutional antibiogram.

CONCLUSION

mRDTs have demonstrated the ability to be one of the most powerful antimicrobial stewardship interventions. Pharmacists required to implement an ASP in their institution should consider mRDTs as standard of care for patients with BSIs.

An Automated, Pharmacist-Driven Initiative Improves Quality of Care for Staphylococcus aureus Bacteremia

Background

Infectious diseases (ID) consultation and antimicrobial stewardship intervention have been shown to improve the management of Staphylococcus aureus bacteremia (SAB). As the workload of antimicrobial stewardship programs (ASPs) continues to increase, ASPs must find a way to maximize the efficiency of the program while optimizing patient outcomes. The objective of this study was to evaluate the impact of incorporating health informatics into the management of SAB via a pharmacist-driven initiative.

Methods

Retrospective, single-center quasi-experimental study of hospitalized patients with SAB. During the intervention period, pharmacists were alerted to patients with SAB via a patient scoring tool integrated into the electronic medical record. Pharmacists utilized the scoring tool and the institution's evidence-based practice guideline to make standardized recommendations to promote adherence to SAB quality-of-care measures and encourage ID consultation. The primary outcome was overall compliance along with adherence to individual quality-of-care components. Secondary clinical outcomes were also analyzed.

Results

In sum, 84 patients were identified for study inclusion, 45 in the pre-intervention and 39 in the intervention group. As a whole, all 4 quality-of-care components for the management of SAB were significantly more frequently adhered to in the intervention group (68.9% vs 92.3%; P = .008). The incidence of ID consult improved significantly by almost 20% in the intervention group (75.6% vs 94.9%, P = .015). No statistically significant differences in duration of bacteremia, length-of-stay, infection-related length-of-stay, or readmission were observed between the groups. The incidence of all-cause mortality was 6-fold higher in the pre- intervention group compared to the intervention group (15.6% vs 2.6%, P = .063).

Conclusion

An automated, pharmacist-driven intervention for the management of patients with SAB demonstrated a significant improvement in patients receiving an ID consult, targeted antimicrobial therapy, and adherence to all SAB quality-of-care measures. As antimicrobial stewardship becomes a mandatory aspect of healthcare in all hospitals in the United States, ASPs will be forced to find ways to provide more efficient, impactful, disease state-based patient care. Our study provides the framework for and data to support this intervention in one of the most clinically important infectious diseases.