1100. A Prospective Evaluation of Neurotoxicity Among Patients Receiving Dose-Optimized Cefepime or Meropenem With Concomitant Therapeutic Drug Monitoring

Background

Cefepime (FEP) induced neurotoxicity (NT) may have serious implications for patients (pts). Retrospective studies have employed variable definitions of NT, finding renal impairment and FEP trough concentrations (Cmin) > 20 mg/L as risk factors. Prospective studies comparing antibiotics have not been performed.

Methods

We conducted a prospective study of pts receiving FEP or meropenem (MEM) with neurologic evaluation and therapeutic drug monitoring (TDM). A NT advisory board (NTAB) was established to develop standardized definitions of possible, probable and definitive NT (Fig 1). Cases of potential NT were adjudicated by the NTAB who were blinded to study treatment. FEP and MEM midpoint and Cmin concentrations were measured at steady-state by validated methods.

Results

127 patients were included (70 FEP, 57 MEM). Demographics and treatment characteristics were similar between groups (Fig 2); 63% were in the ICU. FEP and MEM Cmin varied from 1.9 – 140.5 and 0.6 – 31.3 mg/L, respectively. Median FEP Cmin and total exposures (AUC) were 23.1 mg/L and 347.6 hr*mg/L, respectively. Corresponding MEM values were 5.9 mg/L and 124.8 hr*mg/L, respectively. Cmin values were inversely correlated with renal function for both FEP and MEM (P< 0.001). Rates of possible, probable, or definitive NT were 10% and 5% for FEP and MEM, respectively (P=0.51; Fig 3). 16% and 3% of pts with FEP Cmin > or < 20 mg/L had NT, respectively (P=0.11; Fig 4). Median MEM Cmin were 12.3 and 5.4 mg/L among pts with and without NT, respectively (P=0.09; Fig 4). Rates of NT did not vary by infusion length or dose. FEP and MEM exposures were similar between patients with (17%) or without (83%) microbiologic recurrence due to the same pathogen. FEP was discontinued in 4 pts due to NT; no pts stopped MEM due to NT.

Conclusion

Our study is the first to evaluate FEP NT prospectively and compare rates of NT to pts receiving MEM. We established criteria that were applied by a blinded NTAB. In doing so we found rates of NT to be lower than previously reported and not statistically different between FEP and MEM. Cmin values were highly variable and associated with numerically, but not statistically higher rates of NT for both agents. These findings serve as the basis for larger, multicenter studies and justify use of routine TDM to limit NT among high-risk pts.

Disclosures

Brandon Smith, MD, PharmD, Shionogi (Consultant, Advisor or Review Panel member) Alexandra Urban, MD, Neuropace (Consultant) Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support)

308. Secondary Infections in Patients Requiring Extracorporeal Membrane Oxygenation (ECMO) for Severe Acute Respiratory Distress Syndrome (ARDS) due to COVID-19 Pneumonia (PNA)

Background

Rescue ECMO has been used worldwide in patients (pts) with ARDS caused by COVID-19. Bacterial super-infections affect 3.5-14.3% of hospitalized pts with COVID-19. Pts requiring ECMO may be at an increased risk of infection due to their severity of illness, gut translocation and ECMO impact on host immunity.

Methods

This was a retrospective review of pts requiring ECMO for COVID-19 from April 2020-2021 at a single center. Strict definitions of infections (including ventilator-associated PNA, VAP) were in accordance with CDC criteria.

Results

43 ECMO pts with 1065 ECMO days were evaluated. Median age was 53 yrs (range: 21-62) and median BMI was 36.2 (range: 19.4-75.8). 70% were men and 65% were white. 37 patients (86%) experienced a total of 40 infectious episodes with a median onset from ECMO cannulation to first infection of 10.5d (range: 4-50). Median SOFA and SAPSII scores at time of infection were 12 (6-20) and 63 (30-90), respectively. PNA was the most common infection (78%, with 19% of cases complicated by bacteremia and 3% by empyema) (Fig. 1). The most common organisms isolated were Enterobacterales (37%), S. aureus (25%) and P. aeruginosa (16%) (Fig. 2). Only 2% of all organisms were multi-drug resistant. 3 pts had fungal infections (1 candidemia, 2 aspergillus PNA). Duration of ECMO was significantly longer for infected pts (26d, range: 5-92d) vs (11d, range: 3-24d), p=.01. 95% of infected pts had received steroids vs. 67% of uninfected pts, p=0.09. Treatment success at 1 week was 50%, and 24% and 40% of pts had recurrent infections and persistent/recurrent organisms in clinical cultures, respectively. S. aureus (54%) and Enterobacterales (26%) were associated with persistent or recurrent clinical cultures, requiring prolonged antimicrobial therapy. Mortality rate at 30 days was 65% and was significantly higher for pts with infection than those without (67% vs 33%, p=.02).

Conclusion

Super-infection (most commonly PNA) occurred in almost all COVID-19 pts requiring ECMO for &gt;4 days, and was a significant risk factor for death. Recurrent infections among survivors were common, especially when caused by Enterbacterales or S. aureus. Super-infection and mortality rates of ARDS pts on ECMO for COVID-19 were worse than for ARDS pts on ECMO for influenza at our center.

Disclosures

Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) Fernanda P. Silveira, MD, MS, FIDSA, Ansun (Individual(s) Involved: Self): Grant/Research Support; Novartis (Individual(s) Involved: Self): Grant/Research Support; Qiagen (Individual(s) Involved: Self): Grant/Research Support; Shire (Individual(s) Involved: Self): Advisor or Review Panel member, Grant/Research Support; SlieaGen (Individual(s) Involved: Self): Grant/Research Support; Whiscon (Individual(s) Involved: Self): Grant/Research Support Cornelius J. Clancy, MD, Merck (Grant/Research Support)

1291. PROVE (Retrospective Cefiderocol Chart Review) Study of Real-World Outcomes and Safety in the Treatment of Patients with Gram-negative Bacterial Infections in the US and Europe

Background

Gram-negative bacterial resistance is a global health problem. Limited treatment options exist, especially for carbapenem resistant (CR) pathogens containing metallo-β-lactamases (MBLs) and multidrug resistant non-lactose fermenting bacteria. Cefiderocol (CFDC) retains activity against resistant strains. We describe the objectives, design, and early results of PROVE, a real world retrospective study of CFDC use.

Methods

PROVE is a multi-center, chart review study of CFDC use for resistant Gram-negative infections (GNI). Cases were eligible if they received ≥ 72 hrs of CFDC. Demographics, comorbidity, pathogen, infection site, and treatment course were assessed. Outcomes included all-cause 14-day and inpatient mortality and length of stay (LOS). Clinical resolution was defined by documentation that clinical signs and/or symptoms had resolved or improved without relapse.

Results

24 patients who were treated with CFDC at 2 sites were included to date. Median age was 48 years (Range: 19 - 69 years); 33% were female. The most common comorbidity was diabetes (n=7, 29%). Median total ICU LOS was 36 days. Targeted treatment of documented GNI without preceding failure of prior therapy accounted for 71% of CFDC use. Empirical and salvage treatments accounted for 4% and 25% respectively (Table 1). Median time from admission to 1st CFDC dose was 21 days. Acinetobacter baumannii and Pseudomonas aeruginosa accounted for > 75% of isolates (Fig.1). 92% of patients had CR isolates; > 50% were respiratory. Sensitivity to CFDC was tested in 58% of which 71% were sensitive. All-cause 14-day post-CFDC mortality was 13% (95% CI: 2, 27) and overall hospital mortality 25% (95% CI: 6, 44). Clinical resolution was reached in 54% (95% CI: 33, 76). Median post-CFDC LOS was 40 days. Outcomes were stratified by key covariates (Table 2).

Conclusion

We present initial data for real world use of CFDC for resistant GNI. Patients were complex with multiple comorbidities, some hospitalized for long periods before their index GNI. Outcomes largely reflect this patient population. Additional data are needed to determine the optimal role of CFDC. PROVE offers an opportunity to see how CFDC is being utilized in various settings as well as a first look at key, real world outcomes.

Disclosures

Stephen Marcella, MD, MPH, Shionogi, Inc (Employee) Steven Smoke, PharmD, Karius (Advisor or Review Panel member)Shionogi (Scientific Research Study Investigator, Advisor or Review Panel member) Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) David van Duin, MD, PhD, Entasis (Advisor or Review Panel member)genentech (Advisor or Review Panel member)Karius (Advisor or Review Panel member)Merck (Grant/Research Support, Advisor or Review Panel member)Pfizer (Consultant, Advisor or Review Panel member)Qpex (Advisor or Review Panel member)Shionogi (Grant/Research Support, Scientific Research Study Investigator, Advisor or Review Panel member)Utility (Advisor or Review Panel member)

Contemporary Perspective on the Treatment of Acinetobacter baumannii Infections: Insights from the Society of Infectious Diseases Pharmacists

The purpose of this narrative review is to bring together the most recent epidemiologic, preclinical, and clinical findings to offer our perspective on best practices for managing patients with A. baumannii infections with an emphasis on carbapenem-resistant A. baumannii (CRAB). To date, the preferred treatment for CRAB infections has not been defined. Traditional agents with retained in vitro activity (aminoglycosides, polymyxins, and tetracyclines) are limited by suboptimal pharmacokinetic characteristics, emergence of resistance, and/or toxicity. Recently developed and US Food and Drug Administration (FDA)-approved β-lactam/β-lactamase inhibitor agents do not provide enhanced activity against CRAB. On balance, cefiderocol and eravacycline demonstrate potent in vitro activity and are well tolerated, but clinical data for patients with CRAB infections do not yet support widespread use. Given that CRAB has the capacity to infect vulnerable patients and preferred regimens have not been identified, we advocate for combination therapy. Our preferred regimen for critically ill patients infected, or considered to be at high risk for CRAB, includes meropenem, polymyxin B, and ampicillin/sulbactam. Importantly, site of infection, severity of illness, and local epidemiology are essential factors to be considered in selecting combination therapies. Molecular mechanisms of resistance may unveil preferred combinations at individual centers; however, such data are often unavailable to treating clinicians and have not been linked to improved clinical outcomes. Combination strategies may also pose an increased risk for antibiotic toxicity and Clostridioides difficile infection, and should therefore be balanced by understanding patient goals of care and underlying health conditions. Promising therapies that are in clinical development and/or under investigation include durlobactam-sulbactam, cefiderocol combination regimens, and bacteriophage therapy, which may over time eliminate the need for the continued use of polymyxins. Future goals for CRAB management include pathogen-focused treatment paradigms that are based on molecular mechanisms of resistance, local susceptibility rates, and the availability of well-tolerated, effective treatment options.

Cefiderocol for the Treatment of Adult and Pediatric Patients With Cystic Fibrosis and Achromobacter xylosoxidans Infections

Treatment options for Achromobacter xylosoxidans are limited. Eight cystic fibrosis patients with A. xylosoxidans were treated with 12 cefiderocol courses. Pretreatment in vitro resistance was seen in 3 of 8 cases. Clinical response occurred after 11 of 12 treatment courses. However, microbiologic relapse was observed after 11 of 12 treatment courses, notably without emergence of resistance.

Isavuconazole Is as Effective as and Better Tolerated Than Voriconazole for Antifungal Prophylaxis in Lung Transplant Recipients

BACKGROUND

Invasive fungal infections (IFIs) are common following lung transplantation. Isavuconazole is unstudied as prophylaxis in organ transplant recipients. We compared effectiveness and tolerability of isavuconazole and voriconazole prophylaxis in lung transplant recipients.

METHODS

A single-center, retrospective study of patients who received isavuconazole (September 2015-February 2018) or voriconazole (September 2013-September 2015) for antifungal prophylaxis. IFIs were defined by EORTC/MSG criteria.

RESULTS

Patients received isavuconazole (n = 144) or voriconazole (n = 156) for median 3.4 and 3.1 months, respectively. Adjunctive inhaled amphotericin B (iAmB) was administered to 100% and 41% of patients in the respective groups. At 1 year, 8% of patients receiving isavuconazole or voriconazole developed IFIs. For both groups, 70% and 30% of IFIs were caused by molds and yeasts, respectively, and breakthrough IFI (bIFI) rate was 3%. Outcomes did not significantly differ for patients receiving or not receiving iAmB. Independent risk factors for bIFI and breakthrough invasive mold infection (bIMI) were mold-positive respiratory culture and red blood cell transfusion >7 units at transplant. Bronchial necrosis >2 cm from anastomosis and basiliximab induction were also independent risk factors for bIMI. Isavuconazole and voriconazole were discontinued prematurely due to adverse events in 11% and 36% of patients, respectively (P = .0001). Most common causes of voriconazole and isavuconazole discontinuation were hepatotoxicity and lack of oral intake, respectively. Patients receiving ≥90 days prophylaxis had fewer IFIs at 1 year (3% vs 9%, P = .02). IFIs were associated with increased mortality (P = .0001) and longer hospitalizations (P = .0005).

CONCLUSIONS

Isavuconazole was effective and well tolerated as antifungal prophylaxis following lung transplantation.

Achievement of clinical isavuconazole blood concentrations in transplant recipients with isavuconazonium sulphate capsules administered via enteral feeding tube

BACKGROUND

Isavuconazole is a triazole antifungal available in IV and capsule formulation. Prescribing information states that capsules should not be chewed, crushed, dissolved or opened because the drug was not studied in this manner. However, considering the pharmacokinetics of the capsules, we theorized opening and sprinkling the contents into an enteral feeding tube (EFT) would result in adequate absorption and systemic concentrations of isavuconazole.

OBJECTIVES

To determine whether patients receiving isavuconazonium sulphate capsules via EFT would achieve clinical blood concentrations of isavuconazole.

METHODS

Nineteen solid organ and HCT recipients receiving isavuconazole via EFT for prevention or treatment of invasive fungal infection (IFI) were prospectively identified at four academic medical centres in the USA. Patients were included in this evaluation if they received isavuconazole via EFT for at least 5 days and therapeutic drug monitoring (TDM) was performed.

RESULTS

TDM was performed after a median of 7 days (range 6-17) following EFT administration and 15 days (range 7-174) of isavuconazole therapy overall. Median isavuconazole concentration was 1.8 μg/mL (range 0.3-5.2). Median isavuconazole concentrations in patients with or without prior IV administration were 1.8 μg/mL (range 0.3-5.2) and 2.2 μg/mL (range 0.8-3.6; P = 0.896), respectively. Concentrations achieved with the EFT route were similar to or greater than the corresponding concentrations via the IV route in six patients who had TDM performed during both routes of administration.

CONCLUSIONS

It is reasonable to consider opening isavuconazonium sulphate capsules and administering the contents enterally for prevention and treatment of IFI.

Burden of illness in US hospitals due to carbapenem-resistant Gram-negative urinary tract infections in patients with or without bacteraemia

Background

Urinary tract infections (UTIs) are the most common infections caused by Gram-negative bacteria and represent a major healthcare burden. Carbapenem-resistant (CR) strains of Enterobacterales and non-lactose fermenting pathogens further complicate treatment approaches.

Methods

We conducted a retrospective analysis of the US Premier Healthcare Database (2014–2019) in hospitalised adults with a UTI to estimate the healthcare burden of Gram-negative CR UTIs among patients with or without concurrent bacteraemia.

Results

Among the 47,496 patients with UTI analysed, CR infections were present in 2076 (4.4%). Bacteraemia was present in 24.5% of all UTI patients, and 1.7% of these were caused by a CR pathogen. The most frequent CR pathogens were Pseudomonas aeruginosa (49.4%) and Klebsiella pneumoniae (14.2%). Patients with CR infections had a significantly longer hospital length of stay (LOS) (median [range] 8 [5–12] days vs 6 [4–10] days, P < 0.001), were less likely to be discharged home (38.4% vs 51.0%, P < 0.001), had a higher readmission rate (22.6% vs 13.5%, P < 0.001), and had greater LOS-associated charges (mean US$ 91,752 vs US$ 66,011, P < 0.001) than patients with carbapenem-susceptible (CS) infections, respectively. The impact of CR pathogens was greater in patients with bacteraemia (or urosepsis) and these CR urosepsis patients had a significantly higher rate of mortality than those with CS urosepsis (10.5% vs 6.0%, P < 0.001).

Conclusions

Among hospitalised patients with UTIs, the presence of a CR organism and bacteraemia increased the burden of disease, with worse outcomes and higher hospitalisation charges than disease associated with CS pathogens and those without bacteraemia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06229-x.

Molecular epidemiology, natural history and long-term outcomes of multi-drug resistant Enterobacterales colonization and infections among solid organ transplant recipients

BACKGROUND

Multidrug-resistant Enterobacterales (MDR-E), including carbapenem-resistant and third-generation cephalosporin-resistant Enterobacterales (CRE, CefR-E), are major pathogens following solid organ transplantation (SOT).

METHODS

We prospectively studied patients who underwent lung, liver and small bowel transplant from February 2015-March 2017. Weekly peri-rectal swabs (up to 100 days post-transplant) were cultured for MDR-E. Whole genome sequencing (WGS) was performed on gastrointestinal (GI) tract-colonizing and disease-causing isolates.

RESULTS

Twenty-five percent (40/162) of patients were MDR-E GI-colonized. Klebsiella pneumoniae was the most common CRE and CefR-E. K. pneumoniae carbapenemases and CTX-M were leading causes of CR and CefR, respectively. Thirty-five percent of GI-colonizers developed MDR-E infection versus 2% of non-colonizers (p<0.0001). Attack rate was higher among CRE colonizers than CefR-E colonizers (53% versus 21%, p=0.049). GI-colonization and high body mass index were independent risk factors for MDR-E infection (p≤0.004). Thirty-day mortality among infected patients was 6%. However, 44% of survivors developed recurrent infections; 43% of recurrences were late (285 days-3.9 years post-initial infection). Long-term survival (median: 4.3 years post-transplant) did not differ significantly between MDR-E-infected and non-infected patients (71% versus 77%, p=0.56). WGS phylogenetic analyses revealed that infections were caused by GI-colonizing strains, and suggested unrecognized transmission of novel clonal group-258 sublineage CR-K. pneumoniae and horizontal transfer of resistance genes.

CONCLUSIONS

MDR-E GI-colonization was common following SOT, and predisposed patients to infections by colonizing strains. MDR-E infections were associated with low short- and long-term mortality, but recurrences were frequent and often occurred years after initial infections. Findings provide support for MDR-E surveillance in our SOT program.

Early Experience With Meropenem-Vaborbactam for Treatment of Carbapenem-resistant Enterobacteriaceae Infections

Twenty patients with carbapenem-resistant Enterobacteriaceae infections were treated with meropenem-vaborbactam. Thirty-day clinical success and survival rates were 65% (13/20) and 90% (18/20), respectively. Thirty-five percent of patients had microbiologic failures within 90 days. One patient developed a recurrent infection due to meropenem-vaborbactam-nonsusceptible, ompK36 porin mutant Klebsiella pneumoniae.

1298. Population Pharmacokinetics of Ceftazidime-avibactam among Critically-ill Patients with and without Receipt of Continuous Renal Replacement Therapy

Background

Ceftazidime-avibactam (CAZ-AVI) is used to treat multidrug-resistant infections. There are limited pharmacokinetic (PK) data among critically-ill patients (pts) and no dosing recommendations for those receiving continuous renal replacement therapy (CRRT).

Methods

We conducted a PK study of CAZ-AVI among pts with and without CRRT. Serial blood samples were collected at 0 (pre-dose), 2, 4, 6, and 8 hours after CAZ-AVI administration. All doses were infused over 2h. Samples were centrifuged and plasma stored at -80°C until analysis by a Shimadzu Nexera XD UHPLC with a Shimadzu 8045 MS. Transitions were monitored in positive mode for CAZ (m/z 274.05 < 80.05) and negative mode for AVI (264.00 < 95.90). The assay was reproducible and linear over a range of 0.1 – 20 µg/mL for AVI and 1 – 200 µg/mL for CAZ. non-compartmental analyses were used.

Results

96 plasma samples from 20 pts were included in the study. Median age was 56 years (range: 31 – 74), 55% were male, and 90% were in the ICU at the time of collection. CZA dosing regimens included 2.5g IV q 8h (n=15), 1.25g IV q 8h (n=2), 0.94g IV q 24h (n=1), and 0.94g IV q 48h (n=2). 7 pts received CRRT (median blood and dialysate flow rates were 250 mL/min and 2.5 L/h, respectively; 86% received 2.5g IV q 8h) and 2 pts received intermittent hemodialysis (iHD). Among remaining pts, median creatinine clearance (CrCl) by Cockcroft-Gault was 91ml/min (range: 37 – 168 ml/min). PK values for CAZ and AVI are shown in the Table. Individual concentration-time profiles for patients receiving 2.5g IV q 8h are shown in the Figure. For patients receiving 2.5g IV q8h, CAZ and AVI median (IQR) AUCs were 525.6 hr*µg/ml (403.2, 762.0) and 83.7 (57.3, 129.5), respectively. For those on CRRT receiving the same dose, CAZ and AVI median (IQR) AUCs were 450.2 (450.0, 558.4) and 102.4 (100.7, 142.3), respectively. CAZ pharmacodynamics (PD) targets of 100% fT > 1x and 4x MIC were achieved in 90% and 55% of pts, respectively. AVI PD targets of 100% fT > 1 and 2.5µg/mL were achieved in 100% and 80% of pts, respectively. Treatment-emergent adverse events were not reported in any case.

Ceftazidime and avibactam pharmacokinetic parameters among critically-ill patients

Conclusion

Among this cohort of critically-ill pts, CAZ and AVI exposures varied; however, most pts achieved PD targeted exposures, including those patients receiving CRRT and a standard dosing regimen of 2.5g IV q 8h.

Disclosures

Erin K. McCreary, PharmD, Entasis (Advisor or Review Panel member)Summit (Advisor or Review Panel member) Ryan K. Shields, PharmD, MS, Allergan (Advisor or Review Panel member, Research Grant or Support)Entasis (Advisor or Review Panel member)Melinta (Research Grant or Support)Menarini (Consultant)Merck (Advisor or Review Panel member, Research Grant or Support)Shionogi (Advisor or Review Panel member, Research Grant or Support)Summit (Advisor or Review Panel member)Tetraphase (Research Grant or Support)Venatorx (Advisor or Review Panel member, Research Grant or Support)

1627. Tedizolid is Well-tolerated Among Patients Receiving Prolonged Treatment Courses, Including Those Who are Intolerant of Alternative Agents

Background

Tedizolid (TZD) is approved for acute bacterial skin and skin structure infections (ABSSSI), but often used for complicated infections to avoid linezolid (LZD) adverse events (AE), particularly when long-term treatment is indicated. This studied aimed to characterize the tolerability of TZD, including patients (pts) receiving prolonged treatment.

Methods

Retrospective review of pts who received TZD > 72 hours. Thrombocytopenia was defined as a 50% decrease from baseline platelet count. Favorable clinical outcome was defined as completing therapy without an AE or hospital readmission within 30 days.

Results

86 pts accounting for 102 courses were included. Median age of pts was 57 years and 43% were immunocompromised. Median duration of TZD therapy was 8 days (range: 4 – 350) and 32% of courses were >14 days. Common indications were ABSSSI (n=42), bacteremia (n=15), intra-abdominal infection (n=11), and pneumonia (n=10). 47% and 5% of courses were associated with MRSA or VRE and M. abscessus, respectively. 44% of TZD courses were preceded by treatment failure or AE associated with alternative therapies. AEs attributed to LZD were documented in 13 patients: thrombocytopenia (n=11), lactic acidosis (n=1), or both (n=1). Serotonergic agents were administered during 76% of TZD courses; however, no patient developed serotonin syndrome. 8% of TZD courses were stopped prematurely due to AEs that included thrombocytopenia (n=3), gastrointestinal intolerance (n=2), confusion (n=1), eosinophilia (n=1) and thrombocytopenia with lactic acidosis (n=1). All cases of thrombocytopenia occurred in pts with baseline platelets < 100,000 cells/L. 79% of pts receiving > 14 days of TZD completed therapy successfully without AEs. Among pts who failed alternative therapies, 74% were able to tolerate TZD and completed therapy. Overall, 80% of courses were completed with a favorable outcome.

Clinical Outcomes of Extended TZD Therapy

Conclusion

The safety of prolonged TZD treatment is not well-described. In our experience, TZD was well-tolerated, including among pts who failed alternative therapy. No pt receiving concomitant serotonergic agents developed serotonin syndrome and thrombocytopenia occurred exclusively among pts with low baseline platelets. Treatment courses >14 days were not associated with an increase in the rate of AEs.

Disclosures

Rachel V. Marini, PharmD, Merck (Research Grant or Support) Ryan K. Shields, PharmD, MS, Allergan (Advisor or Review Panel member, Research Grant or Support)Entasis (Advisor or Review Panel member)Melinta (Research Grant or Support)Menarini (Consultant)Merck (Advisor or Review Panel member, Research Grant or Support)Shionogi (Advisor or Review Panel member, Research Grant or Support)Summit (Advisor or Review Panel member)Tetraphase (Research Grant or Support)Venatorx (Advisor or Review Panel member, Research Grant or Support)

Discordance Among Antibiotic Prescription Guidelines Reflects a Lack of Clear Best Practices

Background

Antibiotics are among the most frequently administered drugs globally, yet they are often prescribed inappropriately. Guidelines for prescribing are developed by expert committees at international and national levels to form regional standards and by local experts to form hospital guidance documents. Our aim was to assess variability in antibiotic prescription guidelines for both regional standards and individual hospitals.

Methods

A search through 3 publicly accessible databases from February to June 2018 led to a corpus of English language guidance documents from 70 hospitals in 12 countries and regional standards from 7 academic societies.

Results

Guidelines varied markedly in content and structure, reflecting a paucity of rules governing their format. We compared recommendations for 3 common bacterial infections: community-acquired pneumonia, urinary tract infection, and cellulitis. Hospital guidance documents and regional standards frequently disagreed on preferable antibiotic classes for common infections. Where agreement was observed, guidance documents appeared to inherit recommendations from their respective regional standards. Several regional prescribing patterns were identified, including a greater reliance on penicillins over cephalosporins in the United Kingdom and fluoroquinolones in the United States. Regional prescribing patterns could not be explained by antibiotic resistance or costs. Additionally, literature that cited underlying recommendations did not support the magnitude of recommendation differences observed.

Conclusions

The observed discordance among prescription recommendations highlights a lack of evidence for superior treatments, likely resulting from a preponderance of noninferiority trials comparing antibiotics. In response, we make several suggestions for developing guidelines that support best practices of antibiotic stewardship.

Clinical Evolution of AmpC-Mediated Ceftazidime-Avibactam and Cefiderocol Resistance in Enterobacter cloacae Complex Following Exposure to Cefepime

We report 2 independent patients from whom carbapenem and ceftazidime-avibactam-resistant Enterobacter cloacae complex strains were identified. The ceftazidime-avibactam resistance was attributed to a 2-amino acid deletion in the R2 loop of AmpC β-lactamase, which concurrently caused resistance to cefepime and reduced susceptibility to cefiderocol, a novel siderophore cephalosporin.

Plasma and Cerebrospinal Fluid Therapeutic Drug Monitoring of Ceftolozane and Tazobactam During Treatment of Multidrug-Resistant Pseudomonas aeruginosa Meningitis

We report a case of multidrug-resistant Pseudomonas aeruginosa meningitis treated with ceftolozane-tazobactam with concomitant therapeutic drug monitoring of plasma and cerebral spinal fluid. The data suggest that ceftolozane-tazobactam may be an option for select central nervous system infections; however, treatment decisions should be interpreted on a case-by-case basis.

Reduced ceftazidime and ertapenem susceptibility due to production of OXA-2 in Klebsiella pneumoniae ST258

BACKGROUND

OXA-2 is a class D β-lactamase that confers resistance to penicillins, as well as narrow-spectrum cephalosporins. OXA-2 was recently reported to also possess carbapenem-hydrolysing activity. Here, we describe a KPC-2-encoding Klebsiella pneumoniae isolate that demonstrated reduced susceptibility to ceftazidime and ertapenem due to production of OXA-2.

OBJECTIVES

To elucidate the role of OXA-2 production in reduced ceftazidime and ertapenem susceptibility in a K. pneumoniae ST258 clinical isolate.

METHODS

MICs were determined by the agar dilution method. WGS was conducted to identify and compare resistance genes between isolates. Expression of KPC-2 was quantified by quantitative RT-PCR and immunoblotting. OXA-2 was expressed in Escherichia coli TOP10, as well as in K. pneumoniae ATCC 13883, to define the relative contribution of OXA-2 in β-lactam resistance. Kinetic studies were conducted using purified OXA-2 enzyme.

RESULTS

K. pneumoniae 1761 belonged to ST258 and carried both blaKPC-2 and blaOXA-2. However, expression of blaKPC-2 was substantially reduced due to an IS1294 insertion in the promoter region. K. pneumoniae 1761, K. pneumoniae ATCC 13883 and E. coli TOP10 carrying blaOXA-2-harbouring plasmids showed reduced susceptibility to ertapenem and ceftazidime, but meropenem, imipenem and cefepime were unaffected. blaOXA-2 was carried on a 2910 bp partial class 1 integron containing aacA4-blaOXA-2-qacEΔ1-sul1 on an IncA/C2 plasmid, which was not present in the earlier ST258 isolates possessing blaKPC-2 with intact promoters. Hydrolysis of ertapenem by OXA-2 was confirmed using purified enzyme.

CONCLUSIONS

Production of OXA-2 was associated with reduced ceftazidime and ertapenem susceptibility in a K. pneumoniae ST258 isolate.

Clinical and Genomic Epidemiology of Carbapenem-Nonsusceptible Citrobacter spp. at a Tertiary Health Care Center over 2 Decades

Carbapenem-nonsusceptible Citrobacter spp. (CNSC) are increasingly recognized as health care-associated pathogens. Information regarding their clinical epidemiology, genetic diversity, and mechanisms of carbapenem resistance is lacking. We examined microbiology records of adult patients at the University of Pittsburgh Medical Center (UMPC) Presbyterian Hospital (PUH) from 2000 to 2018 for CNSC, as defined by ertapenem nonsusceptibility. Over this time frame, the proportion of CNSC increased from 4% to 10% (P = 0.03), as did daily defined carbapenem doses/1,000 patient days (6.52 to 34.5; R2 = 0.831; P < 0.001), which correlated with the observed increase in CNSC (lag = 0 years; R2 = 0.660). Twenty CNSC isolates from 19 patients at PUH and other UPMC hospitals were available for further analysis, including whole-genome short-read sequencing and additional antimicrobial susceptibility testing. Of the 19 patients, nearly all acquired CNSC in the health care setting and over half had polymicrobial cultures containing at least one other organism. Among the 20 CNSC isolates, Citrobacter freundii was the predominant species identified (60%). CNSC genomes were compared with genomes of carbapenem-susceptible Citrobacter spp. from UPMC and with other publicly available CNSC genomes. Isolates carrying genes encoding carbapenemases (blaKPC-2,blaKPC-3, and blaNDM-1) were also long-read sequenced, and their carbapenemase-encoding plasmid sequences were compared with one another and with publicly available sequences. Phylogenetic analysis of 102 UPMC Citrobacter genomes showed that CNSC from our setting did not cluster together. Similarly, a global phylogeny of 64 CNSC genomes showed a diverse population structure. Our findings suggest that both local and global CNSC populations are genetically diverse and that CNSC harbor carbapenemase-encoding plasmids found in other Enterobacterales.

Fluoroquinolone Prophylaxis Selects for Meropenem-nonsusceptible Pseudomonas aeruginosa in Patients With Hematologic Malignancies and Hematopoietic Cell Transplant Recipients

BACKGROUND

In Pseudomonas aeruginosa, fluoroquinolone exposure promotes resistance to carbapenems through upregulation of efflux pumps and transcriptional downregulation of the porin OprD. Evidence of this effect among hematologic malignancy (HM) patients or hematopoietic cell transplant (HCT) recipients receiving fluoroquinolone prophylaxis for neutropenia is lacking.

METHODS

We retrospectively evaluated episodes of P. aeruginosa bloodstream infections in HM patients or HCT recipients over a 7-year period at our institution. We determined the association of fluoroquinolone prophylaxis at the time of infection with meropenem susceptibility of P. aeruginosa breakthrough isolates and risk factors for meropenem nonsusceptibility. Whole-genome sequencing (WGS) and phenotypic assessments of meropenem efflux pump activity were performed on select isolates to determine the mechanisms of meropenem resistance.

RESULTS

We analyzed 55 episodes of P. aeruginosa bacteremia among 51 patients. Breakthrough bacteremia while on fluoroquinolone prophylaxis was associated with nonsusceptibility to meropenem, but not to antipseudomonal β-lactams or aminoglycosides. The receipt of fluoroquinolone prophylaxis was independently predictive of bacteremia with a meropenem-nonsusceptible isolate. All meropenem-nonsusceptible isolates analyzed by WGS contained oprD inactivating mutations, and all meropenem-nonsusceptible isolates tested demonstrated reductions in the meropenem minimum inhibitory concentration in the presence of an efflux pump inhibitor. A phylogenetic analysis based on WGS revealed several clusters of closely related isolates from different patients.

CONCLUSIONS

Fluoroquinolone prophylaxis in HM patients and HCT recipients is associated with breakthrough bacteremia with meropenem-nonsusceptible P. aeruginosa strains, likely due to both mutations increasing efflux pump activity and the epidemiology of P. aeruginosa bloodstream infections in our patient population.

Structural Basis of Reduced Susceptibility to Ceftazidime-Avibactam and Cefiderocol in Enterobacter cloacae Due to AmpC R2 Loop Deletion

Ceftazidime-avibactam and cefiderocol are two of the latest generation β-lactam agents that possess expanded activity against highly drug-resistant bacteria, including carbapenem-resistant Enterobacterales Here, we show that structural changes in AmpC β-lactamases can confer reduced susceptibility to both agents. A multidrug-resistant Enterobacter cloacae clinical strain (Ent385) was found to be resistant to ceftazidime-avibactam and cefiderocol without prior exposure to either agent. The AmpC β-lactamase of Ent385 (AmpCEnt385) contained an alanine-proline deletion at positions 294 and 295 (A294_P295del) in the R2 loop. AmpCEnt385 conferred reduced susceptibility to ceftazidime-avibactam and cefiderocol when cloned into Escherichia coli TOP10. Purified AmpCEnt385 showed increased hydrolysis of ceftazidime and cefiderocol compared to AmpCEnt385Rev, in which the deletion was reverted. Comparisons of crystal structures of AmpCEnt385 and AmpCP99, the canonical AmpC of E. cloacae complex, revealed that the two-residue deletion in AmpCEnt385 induced drastic structural changes of the H-9 and H-10 helices and the R2 loop, which accounted for the increased hydrolysis of ceftazidime and cefiderocol. The potential for a single mutation in ampC to confer reduced susceptibility to both ceftazidime-avibactam and cefiderocol requires close monitoring.

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.

Case Commentary: the Need for Cefiderocol Is Clear, but Are the Supporting Clinical Data?

Cefiderocol is a newly approved siderophore cephalosporin that demonstrates expanded in vitro activity against multidrug-resistant Gram-negative bacteria. In two challenging cases reported here, cefiderocol shows potential utility as salvage therapy against difficult-to-treat pathogens with limited or no treatment options; however, two multicenter, randomized clinical trials have yielded mixed results among cefiderocol-treated patients. Taken together, clinicians must balance a clear need for cefiderocol in clinical practice with the uncertainties that have stemmed from the available data.

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.

485. Clinical and Molecular Epidemiology of Carbapenem Non-susceptible Citrobacter sp

Background

Carbapenem non-susceptible Citrobacter sp. (CNSC) are becoming increasingly recognized as healthcare-associated (HA) pathogens, but data on clinical and molecular epidemiology, species diversity and mechanisms of carbapenem resistance are lacking.

Methods

We reviewed patients at University of Pittsburgh Medical Center with CNSC positive cultures from 2000 to 2018. The diversity of CNSC species among a subset of isolates from all UPMC sites was confirmed by 16S rRNA typing, and the presence of carbapenemase enzymes in the same isolates was determined by PCR amplificon. Minimum inhibitory concentrations (MICs) were determined by broth microdilution. Significance of epidemiological trends over time was determined by linear regression, and correlation with antibiotic consumption was determined by cross-correlation using STATA v15.

Results

Between 2000 and 2018, 3% (78/2817) of all Citrobacter sp. were CNS. CNSC rates increased from 4% in 2000 to 10% in 2018 (R² = 0.206, P = 0.05), as did carbapenem consumption (6.5–34.5 DDDs/1000, R² = 0.831, P < 0.001) (Figure 1). Twenty-one isolates from 19 patients were available for additional analysis. Patients had multiple comorbidities (84%), frequently acquired CNSC in the healthcare setting (84%), were colonized with other organisms (68%), and had high rates of in-hospital mortality/discharge to hospice (47%) (Table 1). C. freundii was the dominant species identified (16/21), followed by C. farmeri (2/21), C. koseri (2/21), and C. werkmanii (1/21). Carbapenemases were identified in 14 isolates, including KPC (n = 12), NDM (n = 2), and OXA-48 (n = 1) (Table 2). Isolates were frequently susceptible to ceftazidime–avibactam (MIC median [IQR]: 2[0.5,8]) 81%) and meropenem-vaborbactam (86%) (MIC median [IQR] 0.12[0.3,0.5]) (Table 2).

Conclusion

CNSC species are diverse, have emerged as an HA pathogen at our center, and cause high rates of mortality. Further studies, including ongoing genome sequencing and analysis, are required to better elucidate CNSC diversity and resistance mechanisms.

Disclosures

All authors: No reported disclosures.

710. In Vitro Activity and Performance of Available Susceptibility Testing Methods for Eravacycline Against Carbapenem-Resistant Enterobacteriaceae (CRE)

Background

Eravacycline (ERV) is a recently-approved, fully synthetic fluorocycline agent that demonstrates broad in vitro activity against multidrug-resistant pathogens. We sought to compare the activity of ERV with minocycline (MIN) and tigecycline (TGC) against diverse CRE clinical isolates, and to evaluate the performance of commercially-available susceptibility testing methods.

Methods

ERV, MIN, and TGC minimum inhibitory concentrations (MICs) were determined in triplicate by broth microdilution against previously characterized CRE isolates. ERV susceptibility was also measured by disk diffusion (20 µg disk; Mast Group) and MIC test strips (MTS; Liofilchem) according to manufacturer instructions.

Results

148 CRE were tested, including 92 K. pneumoniae, 32 Enterobacter spp, 11 E. coli, 5 C. freundii, 4 K. oxytoca, and 4 S. marcescens. 72% of isolates harbored bla_KPC, which encoded KPC-2 (n = 33), KPC-3 (n = 48), and other KPC variants (n = 22). 77% and 19% of isolates were resistant to meropenem and ceftazidime–avibactam, respectively. By BMD, the ERV, MIN, and TGC MIC range, MIC50 and MIC90 for shown in the Table. ERV MICs were ≥2-fold lower than MIN and TGC against 99% and 43% of isolates, respectively. ERV MICs did not vary by species or KPC-subtype. ERV MICs determined by BMD and MTS were well-correlated showing 89% essential agreement (MIC within one 2-fold dilution; Figure). The rate of categorical agreement (CA) was 73%. By comparison, the CA rate between BMD and disk diffusion was 78%. By both MTS and disk diffusion methods, susceptibility results clustered on either side of the susceptibility breakpoint. 50% of disk diffusion zones clustered between 14 and 16 millimeters (mm), which is 1 mm on either side of the susceptibility breakpoint (≥15 mm).

Conclusion

This study confirms the in vitro activity of ERV against CRE clinical isolates, which is comparable to TGC. ERV MTS demonstrated high rates of EA, but lower rates of CA. Clinicians should be aware of the nuances of ERV susceptibility testing and recognize that the modal distribution of ERV MICs against CRE lies on either side of the susceptibility breakpoint.

Disclosures

All authors: No reported disclosures.