Treatment with linezolid for VRE-BSI resulted in significantly higher treatment failure in comparison to daptomycin. Linezolid treatment was also associated with greater 30-day all-cause mortality and microbiologic failure in this cohort.

High-dose daptomycin was associated with improved survival and microbiological clearance in VRE-BSI.

Background We conducted this study to describe the clinical characteristics, microbiology, and outcomes of patients treated with ceftazidime-avibactam (CZA) for a range of multidrug-resistant Gram-negative (MDR-GN) infections. Methods This is a multicenter, retrospective cohort study conducted at 6 medical centers in the United States between 2015 and 2019. Adult patients who received CZA (≥72 hours) were eligible. The primary outcome was clinical failure defined as a composite of 30-day all-cause mortality, 30-day microbiological failure, and/or failure to resolve or improve signs or symptoms of infection on CZA. Results In total, data from 203 patients were evaluated. Carbapenem-resistant Enterobacteriaceae (CRE) and Pseudomonas spp were isolated from 117 (57.6%) and 63 (31.0%) culture specimens, respectively. The most common infection sources were respiratory (37.4%), urinary (19.7%), and intra-abdominal (18.7%). Blood cultures were positive in 22 (10.8%) patients. Clinical failure, 30-day mortality, and 30-day recurrence occurred in 59 (29.1%), 35 (17.2%), and 12 (5.9%) patients, respectively. On therapy, CZA resistance developed in 1 of 62 patients with repeat testing. Primary bacteremia or respiratory tract infection and higher SOFA score were positively associated with clinical failure (adjusted odds ratio [aOR] = 2.270, 95% confidence interval [CI] = 1.115–4.620 and aOR = 1.234, 95% CI = 1.118–1.362, respectively). Receipt of CZA within 48 hours of infection onset was protective (aOR, 0.409; 95% CI, 0.180–0.930). Seventeen (8.4%) patients experienced a potential drug-related adverse effect (10 acute kidney injury, 3 Clostridioides difficile infection, 2 rash, and 1 each gastrointestinal intolerance and neutropenia) Conclusions Ceftazidime-avibactam is being used to treat a range of MDR-GN infections including Pseudomonas spp as well as CRE.

Daptomycin MICs for enterococci are typically 1-to 2-fold higher than those for Staphylococcus aureus, and there is an imminent need to establish the optimal dose for appropriate treatment of enterococcal infections. We investigated the bactericidal activity of daptomycin at various dose exposures compared to that of linezolid against vancomycin-resistant enterococcus (VRE) in an in vitro pharmacokinetic/pharmacodynamic model utilizing simulated endocardial vegetations over 96 h. Daptomycin at doses of 6, 8, 10, and 12 mg/kg of body weight/day and linezolid at a dose of 600 mg every 12 h were evaluated against two clinical vancomycin-resistant Enterococcus faecium strains (EFm11499 and 09-184D1051), one of which was linezolid resistant (09-184D1051), and one clinical vancomycin-resistant Enterococcus faecalis strain (EFs11496). Daptomycin MICs were 4, 2, and 0.5 g/ml for EFm11499, 09-184D1051, and EFs11496, respectively. Bactericidal activity, defined as a >3 log 10 CFU/g reduction from the initial colony count, was demonstrated against all three isolates with all doses of daptomycin; however, bactericidal activity was not sustained with the daptomycin 6-and 8-mg/kg/day regimens. Linezolid was bacteriostatic against EFm11499 and displayed no appreciable activity against 09-184D1051 or EFs11496. Concentration-dependent killing was displayed with more sustained reduction in colony count (3.58 to 6.46 and 5.89 to 6.56 log 10 CFU/g) at 96 h for the simulated regimen of daptomycin at doses of 10 and 12 mg/kg/day, respectively (P < 0.012). No E. faecium mutants with reduced susceptibility were recovered at any dosage regimen; however, the E. faecalis strain developed reduced daptomycin susceptibility with daptomycin at 6, 8, and 10 but not at 12 mg/kg/day. Daptomycin displayed a dose-dependent response against three VRE isolates, with high-dose daptomycin producing sustained bactericidal activity. Further research is warranted. D aptomycin (DAP) is a lipopeptide antibiotic with concentration-dependent activity against Gram-positive bacteria that is currently approved for the treatment of staphylococcus bacteremia and right-sided endocarditis at a dose of 6 mg/kg of body weight/day (7). Daptomycin also displays in vitro activity against almost all Enterococcus spp., including those resistant to other antibiotics, such as vancomycin, linezolid (LZD), and quinupristindalfopristin (3, 22, 38). Daptomycin exhibits a lower potency against enterococci than that against staphylococci, demonstrating higher Clinical Laboratory and Standards Institute (CLSI) breakpoints (Յ4 g/ml versus Յ1 g/ml), MIC 50 values (1 to 2 g/ml versus 0.25 g/ml), and MIC 90 values (1 to 2 g/ml versus 0.5 g/ml) (11, 38). Based on in vivo neutropenic mice infection models, maximum concentration (C max )/MIC and area under the concentration-time curve (AUC)/MIC ratios are the best predictors for efficacy of daptomycin against infections caused by both Staphylococcus spp. and Enterococcus spp. (39) Additionally, in vitro pharmacokinetic/pharmacodynamic (P...

Ceftaroline is a novel, broad-spectrum, advanced-generation cephalosporin whose action is mediated by binding to penicillin-binding proteins in bacteria, consistent with other beta-lactam antibiotics. Ceftaroline is distinct in that it has antimicrobial activity against multidrug-resistant Staphylococcus aureus (including methicillin-resistant S. aureus, vancomycin-intermediate S. aureus [VISA], heteroresistant VISA, and vancomycin-resistant S. aureus), Streptococcus pneumonia (including drug-resistant strains), and respiratory gram-negative pathogens such as Moraxella catarrhalis and Haemophilus influenzae (including beta-lactamase-positive strains). Development of resistance to ceftaroline occurs rarely in gram-positive bacteria and at a similar rate to that of other oxyimino-cephalosporins in gram-negative bacteria. The inactive prodrug, ceftaroline fosamil, is administered by intravenous infusion and rapidly undergoes biotransformation to ceftaroline. Ceftaroline then follows a two-compartment pharmacokinetic model and is eliminated primarily by renal excretion, with a half-life of approximately 3 hours. Similar to other cephalosporins, time above the minimum inhibitory concentration is the pharmacodynamic parameter that best predicts efficacy for ceftaroline. Ceftaroline 600 mg intravenously every 12 hours has been shown to have similar efficacy to vancomycin plus aztreonam for the treatment of complicated skin and skin structure infections and to ceftriaxone for the treatment of community-acquired bacterial pneumonia in phase III clinical trials. Ceftaroline displayed a safety profile similar to that of other cephalosporins in clinical trials. Dosage adjustment is required for moderate renal impairment and for patients receiving hemodialysis. Ceftaroline breakpoints have been proposed but not confirmed. Ceftaroline is a renally excreted broad-spectrum cephalosporin that is clinically effective for the treatment of complicated skin and skin structure infections and community-acquired bacterial pneumonia, and it has distinctive activity against some difficult-to-treat multidrug-resistant gram-positive organisms.

Daptomycin is used off-label for enterococcal infections; however, dosing targets for resistance prevention remain undefined. Doses of 4 to 6 mg/kg of body weight/day approved for staphylococci are likely inadequate against enterococci due to reduced susceptibility. We modeled daptomycin regimens in vitro to determine the minimum exposure to prevent daptomycin resistance ( Enterococcus spp. are among the leading causes of nosocomial infections (1). Vancomycin-resistant Enterococcus faecium has been recognized as an important multidrug-resistant pathogen for which new or improved therapies are urgently needed (2, 3). Daptomycin is a lipopeptide antibiotic with potent in vitro bactericidal activity against Gram-positive bacteria, including vancomycin-resistant enterococci (VRE). Although daptomycin lacks an approved indication from the FDA, it is frequently utilized as an alternative agent for the management of VRE infections. However, the optimal pharmacokinetic/pharmacodynamic (PK/PD) targets for resistance prevention and therapeutic success with daptomycin have not been defined (4). In fact, the susceptibility breakpoint designating resistance in enterococci also remains questionable; however, for ease of presentation, we will use the term resistance to refer to nonsusceptible enterococci with daptomycin MICs of Ͼ4 mg/liter. Most experts agree that the daptomycin doses of 4 to 6 mg/kg of body weight/day used for staphylococcal infections are likely inadequate for VRE infections due to reduced susceptibility observed in enterococci (3-5). Daptomycin MIC 50 and MIC 90 are 2 and 4 mg/liter for E. faecium, and 0.5 and 1 mg/liter for Enterococcus faecalis versus 0.25 and 0.5 mg/liter for staphylococci (6). Reports of daptomycin resistance are now becoming more common, emphasizing the need for improved daptomycin dosing paradigms to help preserve the utility of this drug against these difficult to treat pathogens (7-10). Due to the substantial morbidity and mortality associated with enterococcal infections, it is critical to identify characteristics that correlate with treatment failure and therefore improve antimicrobial optimization and patient outcomes.In order to derive daptomycin exposure targets for resistance prevention, we evaluated simulated daptomycin regimens from 4 to 12 mg/kg/day in a 14-day PK/PD model of simulated endocardial vegetations (SEVs) against two daptomycin-susceptible clinical VRE strains (E. faecium S447 and E. faecalis S613). Resistant strains derived from these models were then subjected to a variety of phenotypic and genotypic analyses to evaluate characteristics associated with development of daptomycin resistance. MATERIALS AND METHODSBacterial strains. Two daptomycin-susceptible and vancomycin-resistant enterococcal strains, E. faecalis S613 and E. faecium S447 recovered from the bloodstream and urine, respectively, of patients before daptomycin therapy, were evaluated (11, 12). Both isolates developed daptomycin-resistant derivatives in vivo during daptomycin therapy (11, 12) and

Our objective was to describe the prescribing practices, clinical characteristics, and outcomes of patients treated with ceftolozane-tazobactam (C/T) for multidrug-resistant (MDR) Gram-negative infections. This was a multicenter, retrospective, cohort study at eight U.S. medical centers (2015 to 2019). Inclusion criteria were age ≥18 years and receipt of C/T (≥72 hours) for suspected or confirmed MDR Gram-negative infection. The primary efficacy outcome, evaluated among patients with MDR Pseudomonas aeruginosa infections, was composite clinical failure, namely, 30-day all-cause mortality, 30-day recurrence, and/or failure to resolve or improve infection signs or symptoms after C/T treatment. In total, 259 patients were included, and P. aeruginosa was isolated in 236 (91.1%). The MDR and extremely drug-resistant phenotypes were detected in 95.8% and 37.7% of P. aeruginosa isolates, respectively. The most common infection source was the respiratory tract (62.9%). High-dose C/T was used in 71.2% of patients with a respiratory tract infection (RTI) overall but in only 39.6% of patients with an RTI who required C/T renal dose adjustment. In the primary efficacy population (n = 226), clinical failure and 30-day mortality occurred in 85 (37.6%) and 39 (17.3%) patients, respectively. New C/T MDR P. aeruginosa resistance was detected in 3 of 31 patients (9.7%) with follow-up cultures. Hospital-acquired infection and Acute Physiological and Chronic Health Evaluation II (APACHE II) score were independently associated with clinical failure (adjusted odds ratio [aOR], 2.472 and 95% confidence interval [CI], 1.322 to 4.625; and aOR, 1.068 and 95% CI, 1.031 to 1.106, respectively). Twenty-five (9.7%) patients experienced ≥1 adverse effect (9 acute kidney injury, 13 Clostridioides difficile infection, 1 hepatotoxicity, 2 encephalopathy, and 2 gastrointestinal intolerance). C/T addresses an unmet medical need in patients with MDR Gram-negative infections.

Reduced susceptibility to daptomycin has been reported in patients with infections due to methicillinresistant Staphylococcus aureus (MRSA). Although infections with daptomycin-nonsusceptible (DNS) MRSA are infrequent, optimal therapy of these strains has not been determined. We investigated the killing effects of novel antibiotic combinations with daptomycin (DAP) against two clinical DNS MRSA isolates (SA-684 and R6003) in a 72-h in vitro pharmacokinetic/pharmacodynamic (PK/PD) model with simulated endocardial vegetations (SEV). Simulated regimens included DAP at 6 mg/kg every 24 h (q24h) alone or in combination with trimethoprim-sulfamethoxazole (TMP/SMX) at 160/800 mg q12h, linezolid (LIN) at 600 mg q12h, cefepime (CEF) at 2 g q12h, and nafcillin (NAF) at 4 g q4h. Bactericidal activity was defined as a >3-log 10 CFU/g kill. Differences in CFU/g were evaluated between 4 and 72 h by analysis of variance with the Bonferroni post hoc test. DAP MICs were 4 and 2 mg/liter for SA-684 and R6003, respectively. In the PK/PD model, DAP alone was slowly bactericidal, achieving a 3-log 10 kill at 24 and 50 h for SA-684 and R6003, respectively. Against SA-684, DAP plus TMP/SMX, CEF, LIN, or NAF was bactericidal at 4, 4, 8, and 8 h, respectively, and maintained this activity for the 72-h study duration. DAP plus TMP/SMX or CEF exhibited superior killing than DAP alone against SA-684 between 4 and 72 h, and overall this was significant (P < 0.05). Against R6003, DAP plus TMP/SMX was bactericidal (8 h) and superior to DAP alone between 8 and 72 h (P < 0.001). The unique combination of DAP plus TMP/SMX was the most effective and rapidly bactericidal regimen against the two isolates tested and may provide a clinical option to treat DNS S. aureus infections.